Note: Descriptions are shown in the official language in which they were submitted.
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SUBTERRANEAN FORMATION CHARACTERIZATION USING
MICROELECTROMECHANICAL SYSTEM (MEMS) DEVICES
TECHNICAL FIELD
The present disclosure relates generally to subterranean hydrocarbon
production and, more particularly, to characterizing subterranean formations
using
microelectromechanical system (MEMS) devices.
BACKGROUND
Natural resources, such as hydrocarbons and water, are commonly obtained
from subterranean formations that may be located onshore or offshore. The
development of subterranean operations and the processes for removing natural
resources typically involve a number of different steps such as, for example,
drilling a
borehole at a desired well site, treating the borehole to optimize production
of the
natural resources, and performing the necessary steps to produce and process
the
natural resources from the subterranean formation.
Subterranean operations may be facilitated by characterizing or obtaining
information about the subterranean formation. For example, it may be desirable
to
characterize fractures within the subterranean formation or to obtain
information
about various characteristics such as formation temperature, chemistry, or
nuclear
radiation. However, because the formation may be deep underground and subject
to
extremes in temperature, pressure, and acoustic vibration, traditional
information
gathering techniques may not be practical or possible.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present disclosure and its features
and advantages, reference is now made to the following description, taken in
conjunction with the accompanying drawings, in which:
FIG. 1 is an exemplary formation characterization system associated with a
drilling system;
FIG. 2 is a block diagram of an exemplary MEMS analysis subsystem coupled
to exemplary MEMS scanners for use in a formation characterization system;
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FIG. 3A is an exemplary MEMS device encapsulated by an exemplary
capsule;
FIG. 3B is an exemplary MEMS device partially encapsulated by an
exemplary capsule which has degraded;
FIG. 4 is an exemplary set of MEMS devices encapsulated by exemplary
capsules emulating physical attributes of fluids disposed downhole within a
subterranean formation or solids disposed within the fluids;
FIG. 5 is an exemplary set of solids disposed in a circulating fluid within a
wellbore surrounded by a subterranean formation that includes flactures;
FIG. 6A is an exemplary set of solids disposed in a circulating fluid within a
wellbore surrounded by a subterranean formation that includes a breathing
fracture;
and
FIG. 6B is an exemplary set of solids disposed in a circulating fluid within a
wellbore surrounded by a subterranean formation that includes a breathing
fracture.
DETAILED DESCRIPTION
The present disclosure describes systems and methods for characterizing a
subterranean formation to facilitate hydrocarbon production.
Determining
temperature, chemical, nuclear radiation, and/or other characteristics of a
formation
may facilitate good decision making in relation to subterranean operations.
Additionally, certain formations may include fractures that form and/or
develop while
hydrocarbon production is ongoing. Because fractures and various abnormalities
in
formation characteristics may introduce risk, expense, and/or other
undesirable
elements to hydrocarbon production, it may be desirable to plug fractures to
isolate a
wellbore from the surrounding formation and/or to determine the
characteristics so
that proper measures may be taken to address abnormalities.
A subterranean formation may be characterized by small devices configured to
carry and/or detect information as they circulate through the formation. When
information carried and/or detected by the devices is received and analyzed,
characteristics of the formation may be determined. For
example,
microelectromechancial system (MEMS) devices may be adapted to circulate
through
the formation and to carry and/or detect information. Certain MEMS devices may
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have a machine-scannable designator to allow a MEMS scanner to identify the
MEMS devices wirelessly and/or from some distance. When built to be
sufficiently
rugged for subterranean conditions, MEMS devices may be disposed in a
circulating
fluid and may be circulated in a wellbore with the circulating fluid to
facilitate
characterizing a formation. For example, MEMS devices may facilitate detecting
that
fractures exist, determining approximate sizes of the fractures, determining
approximate locations of the fractures, determining whether the fractures are
breathing fractures, and so on. In other examples, MEMS devices may be
affected by
formation characteristics such as temperatures, chemical properties, or
nuclear
radiation. Determining the effects of such formation characteristics on the
MEMS
devices may reveal information about these characteristics of the formation.
Embodiments of the present disclosure and its advantages may be understood by
referring to FIGS. 1 through 6, where like numbers are used to indicate like
and
corresponding parts.
FIG. 1 illustrates an exemplary formation characterization system associated
with a drilling system. Although the present disclosure describes formation
characterization systems integrated with drilling systems, persons of skill in
the art
will recognize that formation characterization systems may exist in any
suitable
context and at any stage of subterranean hydrocarbon production. For example,
in
some embodiments, formation characterization systems may be associated with
hydrocarbon production in completed wellbores and may thus be integrated with
well
systems having additional, fewer, or different elements than those described
herein in
reference to drilling system 100.
Moreover, although a single formation
characterization system 150 is shown in FIG. 1, two or more formation
characterization systems or may be associated with a single drilling system.
As shown in FIG. 1, drilling system 100 may include well surface or well site
106. Various types of drilling equipment such as a rotary table, circulating
fluid
pumps and circulating fluid tanks (not expressly shown) may be located at well
surface or well site 106. For example, well site 106 may include drilling rig
102 that
may have various characteristics and features associated with a "land drilling
rig."
However, downhole drilling tools incorporating teachings of the present
disclosure
may be satisfactorily used with drilling equipment located on offshore
platforms, drill
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ships, semi-submersibles, and drilling barges (not expressly shown).
Drilling system 100 may also include drill string 103 associated with drill
bit
101 that may be used to form a wide variety of wellbores or bore holes within
subterranean formation 107 such as generally vertical wellbore 114, a
generally
horizontal wellbore (not shown), a directional wellbore (not shown), or any
combination thereof.
Bottom Hole Assembly (BHA) 120 may be formed from a wide variety of
components configured to form wellbore 114. For example, components 122a, 122b
and 122c of BHA 120 may include, but are not limited to, drill bits (e.g.,
drill bit 101),
coring bits, drill collars, rotary steering tools, directional drilling tools,
downhole
drilling motors, reamers, hole enlargers or stabilizers. The number and types
of
components 122 included in BHA 120 may depend on anticipated downhole drilling
conditions and the type of wellbore that will be formed by drill string 103
and rotary
drill bit 101. BHA 120 may also include various types of well logging tools
(not
expressly shown) and other downhole tools associated with directional drilling
of a
wellbore. Further, BHA 120 may also include a rotary drive (not expressly
shown)
connected to components 122a, 122b and 122c and which rotates at least part of
drill
string 103 together with components 122a, 122b and 122c.
Drilling system 100 may also include rotary drill bit ("drill bit") 101. Drill
bit
101 may include one or more blades 126 that may be disposed outwardly from
exterior portions of rotary bit body 124 of drill bit 101. Blades 126 may be
any
suitable type of projections extending outwardly from rotary bit body 124.
Drill bit
101 may rotate with respect to bit rotational axis 104 in a direction defined
by
directional arrow 105. Blades 126 may include one or more cutting elements 128
disposed outwardly from exterior portions of each blade 126. Drill bit 101 may
have
many different designs, configurations, and/or dimensions according to the
particular
application of drill bit 101.
Wellbore 114 may be defined in part by casing string 110 that may extend
from well surface 106 to a selected downhole location. Portions of wellbore
114, as
shown in FIG. 1, that do not include casing string 110 may be described as
"open
hole." Various types of circulating fluid may be pumped from well surface 106
through drill string 103 to attached drill bit 101. Circulating fluid may be
pumped
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into drill string 103 at fluid injection point 130. Circulating fluid may flow
from fluid
injection point 130 through drill string 103 in a downhole direction as
illustrated by
fluid flow 132. At drill bit 101, the circulating fluid may pass through
nozzles of drill
bit 101 to be ejected into wellbore 114. The circulating fluid may then be
circulated
back to well surface 106 through annulus 108 as illustrated by fluid flow 134.
As
shown, annulus 108 may be defined in part by outside diameter 112 of drill
string 103
and inside diameter 118 of wellbore 114. Inside diameter 118 may be referred
to as
the "sidewall" of wellbore 114. Annulus 108 may also be defined by outside
diameter
112 of drill string 103 and inside diameter 111 of casing string 110.
As shown, elements of formation characterization system 150 may be
integrated with drilling system 100. In certain embodiments, MEMS analysis
subsystem 140 may be located at or near well site 106. MEMS analysis subsystem
140 may be communicatively coupled with MEMS scanner 142, which may also be
located near well site 106. In other embodiments, MEMS analysis subsystem 140,
MEMS scanner 142, and/or one or more components thereof may be located
elsewhere, such as downhole within wellbore 114. For example, MEMS scanner 142
may be permanently located at a fixed point in wellbore 114 or may be
associated
with drill string 103 or BHA 120. By communicating with MEMS scanner 142,
MEMS analysis subsystem 140 may compile data representing a set of MEMS
devices that have entered or are located within wellbore 114. For example,
MEMS
analysis subsystem 140 may store data associated with a designator of each
MEMS
device disposed in the circulating fluid as the MEMS devices enter wellbore
114 (e.g.,
by entering drill string 103).
As shown, MEMS analysis subsystem 140 may also be communicatively
coupled with MEMS scanner 144. MEMS scanner 144 may also be at or near well
site 106, as shown, downhole within wellbore 114, or in any suitable location.
For
example, MEMS scanner 144 may be located at a position on well surface 106
where
circulating fluid emerges from wellbore 114 after circulating through wellbore
114
(e.g., by emerging from annulus 108). As such, in various embodiments, MEMS
scanner 144 may be located apart from MEMS scanner 142, near MEMS scanner 142,
or may even be integrated with MEMS scanner 142. By communicating with MEMS
scanner 144, MEMS analysis subsystem 140 may receive information about a
subset
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of MEMS devices that emerge from wellbore 114 in response to circulation of
the
circulating fluid in wellbore 114. In response, MEMS analysis subsystem 140
may
determine that certain MEMS devices in the subset have been affected by
temperature, radiation, or chemical properties of the formation due to changes
in the
designator detected as compared to when the designator was scanned by MEMS
scanner 142. In other examples, MEMS analysis subsystem 140 may determine that
the subset of MEMS devices received is different from the set of MEMS devices
sent
downhole. Accordingly, MEMS analysis subsystem 140 may characterize one or
more fractures within the formation by inferring that MEMS devices present in
the set
but missing from the subset were captured by fractures within formation 107.
As shown in FIG. 1, formation 107 may have one or more fractures. The
fractures in formation 107 may be naturally occurring and inherent to
formation 107,
or created by drilling operations or other subterranean operations performed
within
wellbore 114. Fractures 136 (e.g., fractures 136a, 136b, and 136c) are shown
within
formation 107 in FIG. 1. While FIG. 1 shows only three fractures 136,
additional or
fewer fractures of any size may be present in formation 107. Fractures 136 are
not
drawn to scale relative to formation 107 or any elements of drilling system
100 or
formation characterization system 150. However, relative size differences
between
fractures 136 may be reflected by the size of each fracture 136 as drawn. For
example,
as shown, fracture 136a may be a relatively large fracture. As such, fracture
136a
may be of significant concern to operators associated with drilling system
100.
Fracture 136b may be a medium-sized fracture. Fracture 136c may be a smaller
fracture. Because of their sizes, fractures 136b and 136c may be of less
concern to
operators than fracture 136a. However, characterizing all three fractures 136
in
formation 107 may be desirable so that downhole conditions may be
comprehensively
understood.
To characterize formation 107, including obtaining information about
fractures 136, MEMS devices may be adapted to be carried by circulating fluid
into
formation 107 (e.g., by fluid flows 132 and 134 in wellbore 114). In some
examples,
MEMS devices will react to temperature, radiation, or chemical characteristics
of the
formation such that the designators of the MEMS devices will modified.
Accordingly, as will be described in more detail below, MEMS analysis
subsystem
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140 may detect that certain MEMS devices have reacted to the characteristics
of the
formation due to the modified designators. In other examples, the MEMS devices
may be carried into fractures 136 from wellbore 114 as part of the natural
course of
fluid flow 134 of the circulating fluid. Accordingly, certain MEMS devices may
be
removed, at least temporarily, from fluid flow 134 as the MEMS devices are
captured
by fractures 136 (e.g., by becoming stuck or otherwise disposed within
fractures 136).
Meanwhile, other MEMS devices may continue circulating in wellbore 114 to
eventually emerge from wellbore 114 at well surface 106. Thus, as will be
described
in more detail below, MEMS analysis subsystem 140 may detect and/or otherwise
characterize fractures 136 by inferring information from the set of MEMS
devices that
entered wellbore 114, the subset of MEMS devices that emerged from wellbore
114,
and the MEMS devices missing from the subset because they were captured by
fractures 136.
In certain embodiments, MEMS devices may be tracked by one or more
MEMS scanners located along any portion of wellbore 114 while the MEMS devices
are carried by fluid flows 132 and 134 throughout wellbore 114. For example,
MEMS devices may be scanned by one or more MEMS scanners located along drill
string 103 (not shown). In certain embodiments, one or more MEMS scanners may
also be associated with a wireline employed within wellbore 114 (not shown).
FIG. 2 illustrates a block diagram of an exemplary MEMS analysis subsystem
coupled to exemplary MEMS scanners for use in a formation characterization
system.
In FIG. 2, formation characterization system 200 may represent an embodiment
of
formation characterization system 150 described above with respect to FIG. 1.
As
shown, formation characterization system 200 may include MEMS analysis
subsystem 202. MEMS analysis subsystem 202 may represent an embodiment of
MEMS analysis subsystem 140, described above with respect to FIG. 1. Formation
characterization system 200 may also include MEMS scanner 210 and MEMS
scanner 212, which may respectively represent embodiments of MEMS scanner 142
and MEMS scanner 144, described above with respect to FIG. 1. Formation
characterization system 200 may also include one or more displays 216. The
elements shown in FIG. 2 are exemplary only and formation characterization
system
200 may include fewer or additional elements.
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MEMS scanners 210 and 212 may be configured to scan (e.g., read) and/or
assign (e.g., write) machine-scannable designators of any suitable MEMS
device. For
example, MEMS scanners 210 and 212 may scan and or assign designators of
passive
MEMS devices. Passive MEMS devices may include no independent power supply
but may receive any power needed (e.g., to read or write a designator or
perform other
functionality) wirelessly from electromagnetic fields supplied from MEMS
scanners
210 and 212 or from another source. In some examples, passive MEMS devices may
be magnetically encoded with the designator, which MEMS scanners 210 and 212
may be configured to scan.
MEMS scanners 210 and 212 may also be configured to scan and/or assign
multi-unit designators. A unit of a multi-unit designator may include any
suitable
type of data. For example, a unit may be a bit (e.g., 0 or 1), an alphanumeric
character encoded as one or more bytes, or any suitable number (e.g., a
decimal,
hexadecimal, or other number). A multi-unit designator may include a serial
number
and each unit of the multi-unit designator may be an individual digit or
character of
the serial number. The serial number may be unique or may otherwise help
distinguish one designator associated with one MEMS device from other
designators
associated with other MEMS devices in the set disposed in the circulating
fluid of
formation characterization system 200. The designator may also include data
indicative of particular features of the MEMS device. For example, certain
units of a
designator may include a serial number while other units include information
about a
size, shape, density, reactive sensitivity, and/or other characteristic of the
MEMS
device. The designator may also include time data such as a timestamp
indicative of
various events such as when MEMS scanner 210 scanned the MEMS device entering
a wellbore, when MEMS scanner 212 scanned the MEMS device emerging from the
wellbore, and/or other events associated with the MEMS device.
In certain embodiments, MEMS scanners 210 or 212 or another device (not
shown) may dynamically write a designator to one or more MEMS devices as the
set
of MEMS devices disposed within the circulating fluid enters the wellbore
(e.g.,
enters drill string 103, as shown in FIG. 1). For example, MEMS scanner 210
may be
configured to assign each MEMS device a machine-scannable designator such as
the
designators described above. MEMS scanner 210 may dynamically assign the MEMS
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device a unique identification number and/or a timestamp as the MEMS device
enters
the wellbore. In certain examples, the designator of the MEMS device may also
be
altered. For example, the MEMS device may be preprogrammed with static
information about physical characteristics of the MEMS device but may receive
an
identification number and/or a timestamp dynamically from a MEMS scanner or
other
device.
As shown in FIG. 2, MEMS scanners 210 and 212 may be communicatively
coupled to MEMS analysis subsystem 202. Through this communicative coupling,
MEMS analysis subsystem 202 may direct MEMS scanners 210 and 212 to perform
various operations such as scanning and/or assigning designators of MEMS
devices.
MEMS analysis subsystem 202 may also receive information from MEMS scanners
210 and 212 regarding MEMS devices. For example, MEMS analysis subsystem 202
may receive the designators of a set of MEMS devices entering a wellbore from
MEMS scanner 210, and the designators of a subset of MEMS devices emerging
from the wellbore from MEMS scanner 212.
In response to receiving the designators from MEMS scanners 210 and 212,
MEMS analysis subsystem 202 may analyze the designators to characterize a
subterranean formation. To perform the analysis, MEMS analysis subsystem 202
may include various components. For example, as shown in FIG. 2, MEMS analysis
subsystem 202 may include processor 204, memory 206, and storage unit 208
communicatively coupled one to another. Modifications, additions, or omissions
may
be made to MEMS analysis subsystem 202 without departing from the scope of the
present disclosure. For example, MEMS analysis subsystem 202 illustrates one
particular configuration of components, but any suitable configuration of
components
may be used. For example, components of MEMS analysis subsystem 202 may be
implemented either as physical or logical components. Furthermore, in some
embodiments, functionality associated with components of MEMS analysis
subsystem 202 may be implemented with special and/or general purpose circuits
or
components. Components of MEMS analysis subsystem 202 may also be
implemented by computer program instructions.
Processor 204 may include a microprocessor, microcontroller, digital signal
processor (DSP), field programmable gate array (FPGA), application specific
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integrated circuit (ASIC), or any other digital or analog circuitry configured
to
interpret and/or execute program instructions and/or process data. Processor
204 may
be configured to interpret and/or execute program instructions and/or data
stored in
memory 206. Program instructions or data may constitute portions of software
for
carrying out formation characterization as described herein. For example,
program
instructions may cause processor 204 to compare a set of MEMS devices that
entered
a wellbore and a subset of MEMS devices that emerged from the wellbore to
determine that certain MEMS devices were removed from the flow of the
circulating
fluid because they were captured by a downhole fracture, or that the MEMS
devices
emerged in an unexpected order. Program instructions may further cause
processor
204 to infer from the subset of MEMS devices that a fracture is present
downhole
and/or to determine a characteristic of the fracture such as an approximate
size of the
fracture, an approximate location (e.g. downhole depth) of the fracture,
and/or
whether the fracture is a breathing fracture. Various embodiments of
characterizing
fractures are described in more detail below. In other examples, program
instructions
may cause processor 204 to detect that particular units of some multi-unit
designators
of MEMS devices emerging from the wellbore are no longer machine-scannable,
indicating that the MEMS devices may have reacted downhole with temperature,
radiation, chemical, or other characteristics of the formation. Various
embodiments
of determining downhole characteristics are described in more detail below.
Memory 206 may include any system, device, or apparatus configured to hold
one or more memory modules. For example, memory 206 may include read-only
memory, random access memory, solid state memory, or disk-based memory. Each
memory module may include any system, device or apparatus configured to retain
program instructions and/or data for a period of time (e.g., computer-readable
non-
transitory media).
Storage unit 208 may provide and/or store any information that suits a
particular embodiment. For example, storage unit 208 may store designators of
the
set of MEMS devices that enter the wellbore as detected by MEMS scanner 210.
Storage unit 208 may also store designators of the subset of MEMS devices that
emerge from the wellbore, as detected by MEMS scanner 212. Storage unit 208
may
also store values associated with characteristics of the formation including
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characteristics of fractures within the formation, that may be derived or used
by
processor 204. Storage unit 208 may be implemented in any suitable manner,
such as
by functions, instructions, logic, or code, and may be stored in, for example,
a
relational database, file, application programming interface, library, shared
library,
record, data structure, service, software-as-service, or any other suitable
mechanism.
Storage unit 208 may include operational code such as functions, instructions,
or
logic.
MEMS analysis subsystem 202 may present, transfer, respond to, or otherwise
use information obtained from the designators of the set and the subset of
MEMS
devices in any suitable way. For example, in some embodiments, MEMS analysis
subsystem 202 may be communicatively coupled to display 216, whereby MEMS
analysis subsystem 202 may present information obtained or inferred to onsite
and/or
offsite operators associated with the subterranean operations and hydrocarbon
production. MEMS analysis subsystem 202 may produce a distribution plot or
report
that may be displayed on display 216 so that operators may be apprised as to
whether
an abnormal event has occurred. In other examples, MEMS analysis subsystem 202
may also be configured to automatically respond to formation characteristics
that are
determined by automatically altering parameters associated with wellbore 114,
by
setting off alarms, by communicating with real-time decision programs, and/or
by
responding in any other suitable manner.
Referring now to FIGS. 3A and 3B, collectively referred to as FIG. 3,
particular embodiments of MEMS devices adapted for use in subterranean
operations
are illustrated. Specifically, FIG. 3A illustrates an exemplary MEMS device
encapsulated by an exemplary capsule. As shown, MEMS device 302 is
encapsulated
by cylindrical capsule 304.
MEMS device 302 may be adapted for use in subterranean operations to
facilitate hydrocarbon production. For example, MEMS device 302 may be a
passive
MEMS device and may be associated with a designator that may be machine-
scannable from MEMS device 302 while MEMS device 302 is encapsulated in
capsule 304. Specifically, MEMS device 302 may be configured to be machine-
scannable by MEMS scanners 210 and 212, discussed above in reference to FIG.
2, as
MEMS device 302 is disposed in circulating fluid that is entering a wellbore
or
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emerging from the wellbore. MEMS device 302 may have similar or the same
properties discussed in reference to other MEMS devices described above. For
example, MEMS device 302 may be magnetically encoded with a multi-unit
designator including a serial number. Specifically, the multi-unit designator
including
the serial number may be magnetically encoded along length 310 of MEMS device
302. In some examples, a first unit of the multi-unit designator may be
machine-
scannable even if a second unit of the multi-unit designator is not. For
example, one
or more units of the designator magnetically encoded toward bottom end 312 of
MEMS device 302 may be machine-scannable even if other units of the designator
encoded closer to top end 314 are not. In some embodiments, the one or more
units
encoded toward bottom end 312 may be machine-scannable even when a portion of
MEMS device 302 toward top end 314 detaches from the rest of MEMS device 302.
Capsule 304 may also be adapted for use in subterranean operations in
association with MEMS device 302. For example, capsule 304 may be adapted to
withstand high temperature, pressure, acoustic vibration, and other extreme
conditions
common downhole that MEMS device 302 may not be able to withstand alone. As
such, capsule 304 may protect MEMS device 302 as it is carried by circulating
fluid
through the wellbore. In various embodiments, capsule 304 may have a shape,
size,
and/or density that emulates fluids or solids found within the wellbore.
Additional
examples of capsules with different sizes, shapes, and densities are described
below.
In other embodiments, capsule 304 may simply imitate the size, shape, and/or
density
of the MEMS device it encapsulates, as illustrated in FIG. 3.
Capsule 304 may also be adapted for use in subterranean operations to
facilitate hydrocarbon production by including one or more reactive parts and
one or
more nonreactive parts. For example, in FIG. 3A, capsule 304 includes reactive
part
306 and nonreactive part 308. Reactive part 306 may be adapted to react to
various
characteristics within a subterranean formation. For example, the construction
of
reactive part 306 may employ polyamide chemistry to form reactive part 306 of
one
or more reactive polymeric materials that react to various characteristics of
the
formation. Reactive part 306 may react to the temperature of the formation,
nuclear
radiation within the formation, particular chemical properties of the
formation,
acoustic vibrations within the formation, radio frequency electromagnetic
radiation
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within the formation, and/or other suitable characteristics of the formation.
For
example, reactive part 306 may react to temperature by dissolving, softening,
breaking down, or otherwise degrading when it is exposed to a temperature
above a
particular threshold. Similarly, reactive part 306 may degrade as a chemical
reaction
to particular chemical properties present in a formation or as a reaction to
nuclear
radiation present in the formation. When reactive part 306 reacts to a
characteristic of
the formation by degrading, a portion of MEMS device 302 encapsulated by
reactive
part 306 may become exposed. Because MEMS device 302 may not be adapted to
withstand dovvnhole conditions, the exposure of the portion of MEMS device 302
may cause MEMS device 302 to be affected or damaged.
As shown, capsule 304 may also include nonreactive part 308. Nonreactive
part 308 may be nonreactive to one or more particular characteristics of the
formation
that reactive part 306 reacts to. For example, if reactive part 306 is
configured to
react to temperatures above a threshold, nonreactive part 308 may be
configured to
withstand temperatures above the threshold such that nonreactive part 308 does
not
react (e.g., degrade) while reactive part 306 does. In certain embodiments,
nonreactive part 308 may react to certain characteristics of the formation
that are
different from the characteristics that reactive part 306 reacts to. For
example,
reactive part 306 may degrade when certain nuclear radiation is present while
nonreactive part 308 may not react to the nuclear radiation. However,
nonreactive
part 308 may degrade in the presence of certain chemical properties of the
formation
while reactive part 306 may not react to the chemical properties. In certain
examples,
capsule 304 may have more than two parts as shown in FIG. 3. For example,
capsule
304 may have a part that does not react to any formation characteristic, a
part that is
reactive to temperature characteristics, a part that is reactive to nuclear
radiation
characteristics, and a part that is reactive to chemical characteristics. In
the same or
other examples, a variety of capsules configured to react to different
formation
characteristics may be disposed within the circulating fluid together so that
the
different formation characteristics may each be detected.
FIG. 3B illustrates an exemplary MEMS device partially encapsulated by an
exemplary capsule which has degraded. Specifically, as shown in FIG. 3B,
reactive
part 306 of capsule 304 has degraded, exposing a portion of MEMS device 302
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toward top end 314 as illustrated by portion 302-1. Reactive part 306 may have
degraded as a reaction to a temperature above a particular threshold, nuclear
radiation,
a chemical property of the formation, or another characteristic of the
formation that
reactive part 306 was designed to react to. As shown, after reactive part 306
degrades
to expose portion 302-1, portion 302-1 is no longer encapsulated by capsule
304 while
the portion of MEMS device 302 toward bottom end 312, illustrated by portion
302-2,
continues to be encapsulated by nonreactive part 308 of capsule 304. MEMS
device
302 may not be designed to withstand exposure to extreme conditions such as
heat
and pressure in the formation without protection from capsule 304. For
example,
turbulence or other extreme downhole conditions may cause MEMS device 302 to
break such that portion 302-1 detaches from MEMS device 302, as shown. As a
result of the exposure and/or the detachment of portion 302-1, one or more
units of a
multi-unit designator associated with portion 302-1 may become non-machine
scannable by a MEMS scanner. For example, if ten units (e.g., digits) were
magnetically encoded along length 310 of MEMS device 302 in FIG. 3A, three
digits
may be associated with portion 302-1 and seven digits may be associated with
portion
302-2. The three digits associated with portion 302-1 may become non-machine-
scannable when portion 302-1 is exposed and/or detaches. Consequently, when
MEMS device 302 is scanned (e.g., when emerging from the wellbore), only seven
of
the original ten digits may scannable by the MEMS scanner.
The degrading of reactive part 306 and subsequent damage to or detachment
of portion 302-1 of MEMS device 302 may reveal characteristics of the
subterranean
formation within a formation characterization system. For example, as
generally
described above in relation to FIG. 2, MEMS scanner 210, MEMS scanner 212, and
MEMS analysis subsystem 202 may function cooperatively to determine the
characteristic of the subterranean formation that reactive portion 306 reacted
to.
Specifically, in one embodiment, MEMS scanner 210 may detect 10 digits of MEMS
device 302 as it enters the wellbore. Subsequently, MEMS device 302 may react
to a
chemical characteristic of the formation such that reactive part 306 degrades
and
portion 302-1 of MEMS device 302 detaches. After circulating back up to emerge
from the wellbore, MEMS device 302 may only include portion 302-2 and, thus,
MEMS scanner 212 may only scan 7 digits of MEMS device 302. MEMS analysis
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subsystem 202 may receive the 10 digit designator from MEMS scanner 210 and
the 7
digit designator from MEMS scanner 212 and infer that each designator is
associated
with the same MEMS device 302, but that the MEMS device encountered the
chemical characteristic of the formation and was damaged as a result.
Accordingly,
MEMS analysis subsystem 202 may infer that the chemical characteristic is
present in
the formation. Inferring information in this way may help characterize the
formation.
FIG. 4 illustrates an exemplary set of MEMS devices encapsulated by
exemplary capsules emulating physical attributes of fluids disposed downhole
within
a subterranean formation or solids disposed within the fluids. Specifically,
set 400 of
MEMS devices 402 includes a non-uniform assoituient of capsules 404 (e.g.,
capsules
404-1 through 404-6), each capsule 404 encapsulating at least one MEMS device
402.
Although only six MEMS devices 402 are illustrated as part of set 400 in FIG.
4, set
400 may include any number of MEMS devices that suits a particular embodiment.
For example, set 400 may include dozens, hundreds, thousands, or more MEMS
devices 402. In some examples, each MEMS device 402 may be encapsulated by the
non-uniform assoitinent of capsules 404, as shown in FIG. 4. In other
examples, set
400 may also include one or more freestanding MEMS devices that are not
encapsulated by a capsule 404 (not shown).
MEMS devices 402 may be similar to MEMS device 302, described in
relation to FIG. 3. For example, MEMS devices 402 may be adapted for use in
subterranean operations, but may be encapsulated by capsules 404 to help MEMS
devices 402 withstand extreme conditions (e.g., temperature, pressure, etc.)
commonly encountered downhole within a subterranean formation. MEMS devices
402 may also be passive MEMS devices with multi-unit designators that may be
machine-scannable from MEMS devices 402 while MEMS devices 402 are
encapsulated in capsules 404. In various embodiments, MEMS devices 402 may be
each be uniform or identical to one another in appearance and construction.
For
example, to take advantage of benefits associated with economies of scale from
large-
scale manufacturing, MEMS devices 402 may be manufactured to have uniform
sizes,
shapes, and densities. In other embodiments, MEMS devices 402 may vary and/or
may be adapted to have particular physical qualities not shared by all other
MEMS
devices 402.
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Capsules 404 may also be adapted for use in subterranean operations by
having one or more of the attributes of capsule 304 described in relation to
FIG. 3.
For example, as shown, capsules 404 may each encapsulate a MEMS device 402 to
protect MEMS devices 402 from extreme downhole conditions. As such, capsules
404 may be constructed of materials capable of withstanding the extreme
conditions.
In addition, capsules 404 may be configured to react to characteristics of the
formation (e.g., temperature, chemical, nuclear, etc.) as described in
relation to
capsule 304.
Capsules 404 may include a wide assortment of sizes, shapes, and densities.
For example, capsules 404 may be adapted to emulate physical attributes of
various
fluids disposed downhole within a subterranean formation (e.g., hydrocarbon
fluids,
water, circulating fluids, etc.) or solids disposed within the fluids (e.g.,
drill cuttings,
lost circulation material ("LCM") solids, etc.), as will be described in more
detail
below. As shown in FIG. 4, each capsule 404 may have a different size, shape,
density, and/or aspect ratio. For example, set 400 includes MEMS devices 402
encapsulated by pyramidal capsule 404-1, cubic capsule 404-2, spherical
capsule 404-
3, wire-like capsule 404-4, ellipsoidal capsule 404-5, and paper-like capsule
404-6. In
other examples, an assortment of capsules including a plurality of each
capsule type
may be used. For example, set 400 may include dozens, hundreds, thousands, or
more MEMS devices 402 encapsulated by a plurality of pyramidal capsules, a
plurality of cubic capsules, a plurality of spherical capsules, a plurality of
wire-like
capsules, a plurality of ellipsoidal capsules, a plurality of paper-like
capsules, and/or
any combination of these or other types of capsules that suit a particular
embodiment.
For purposes further detailed below in relation to FIGS. 5 and 6, capsules 404
may emulate one or more physical attributes associated with fluids disposed
downhole during subterranean operations and solids disposed within the fluids.
For
example, capsules 404 may emulate a density of a fluid such as water, fluid
hydrocarbons (e.g., oil, gas, etc.), and/or circulating fluids (e.g., drilling
muds,
production fluids, etc.). As such, capsules 404 may be constructed from
ceramic,
polymer, metal, glass, and/or any other suitable material that may have a
density
approximately emulating a fluid disposed downhole during the subterranean
operations. In the same or other examples, capsules 404 may emulate solids
disposed
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within the fluids. For example, capsules 404 may emulate drill cuttings from
the
formation as the wellbore within the formation is created or extended (e.g.,
by drill bit
101 of FIG. 1). Capsules 404 may also emulate lost circulation material
("LCM")
solids sent downhole to help isolate a wellbore from the formation. In certain
examples, capsules 404 may emulate a size, shape, ancUor aspect ratio of
various
solids disposed within the fluids. For example, drill cuttings and/or LCM
solids may
have various shapes and sizes similar to capsules 404 illustrated in FIG. 4.
FIG. 5 illustrates exemplary solids disposed in a circulating fluid within a
wellbore surrounded by a subterranean formation that includes fractures. As
discussed above in reference to FIG. 1, wellbore 114 may be surrounded by
formation
107, which may contain fractures 136 (e.g., fractures 136a, 136b, and 136c).
The
portion of wellbore 114 illustrated in view 500 includes a short length of
casing string
110, but is otherwise open hole. As in FIG. 1, the circulating fluid in FIG. 5
flows in
drill string 103 in a downhole direction indicated by fluid flow 132. After
emerging
from drill string 103 further downhole (e.g., through nozzles of drill bit
101, not
shown), the fluid flows in annulus 108 in an uphole direction illustrated by
fluid flow
134.
As shown, various solids 510 may be disposed within the circulating fluid in
wellbore 114. In certain embodiments, a non-uniform assoi ____________ intent
of solids varying in
size, shape, and/or density may be used. For example, as shown in FIG. 5,
solids 510
form a non-uniform assortment of solids varying in size. In FIG. 5, each solid
510 is
labeled according to its size, where 1 signifies a very small solid, 2
signifies a slightly
larger solid, and so on up to 5, which signifies the largest of solids 510
shown in FIG.
5. Certain solids 510 are labeled with reference signs denoting the size of
the solids
(e.g. solids 510-1 are size 1, solids 510-2 are size 2, etc.). To reduce
clutter with the
large number of solids 510 shown in FIG. 5, certain solids 510 do not include
reference signs. The relative size differences reflected by the labels on
solids 510
differentiates smaller solids 510 (e.g., solids 510-1, 510-2, etc.) from
larger solids 510
(e.g., solids 510-4, 510-5, etc.). However, neither solids 510 nor other
elements
shown in FIG. 5 (e.g., drill string 103, wellbore 114, fractures 136, etc.)
are drawn to
scale relative to one another.
Solids 510 may include any solids suitable for circulation with a circulating
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fluid in a wellbore. For example, solids 510 may include drill cuttings, LCM
solids,
MEMS devices, and/or other solids. Certain solids 510 may be configured to
have a
particular density or to fit within a particular density range. As such,
certain solids
510 may have a density allowing them to be suspended in a particular fluid
disposed
in or around wellbore 114 or formation 107. For example, solids may be
suspended
within a hydrocarbon fluid (e.g., oil, gas, etc.), water, drilling mud,
completion fluid,
cement, or any other suitable fluid. When a solid is suspended within a fluid,
the
solid may have a similar density as the fluid such that the solid does not
substantially
float or sink within a volume of the fluid. When the solid is suspended within
the
fluid, the solid may naturally follow the flow of the fluid as the fluid is
pumped
downhole (e.g., following fluid flow 132), as the fluid circulates uphole
(e.g.,
following fluid flow 134), and as the fluid otherwise flows within formation
107. For
example, solids suspended within a circulating fluid may enter fractures 136
as the
circulating fluid flows into fractures 136.
Certain solids 510 may also be a particular size or may fit within a
particular
size range. For example, solids 510 may be sized and/or shaped to traverse
drill string
103 and be ejected out of nozzles on drill bit 101. Solids 510 may also be
sized and
shaped to facilitate coating sidewall 118 and/or plugging one or more
fractures 136.
For example, certain solids 510 may be small enough to fit within particular
fractures
136 (e.g., fracture 136a) and thus may tend to accumulate in the particular
fractures
136, eventually plugging up the fractures. At the same time, the same solids
510 that
fit in larger fractures may be too large to fit in smaller fractures 136
(e.g., fracture
136c) and may be carried past the smaller fractures by fluid flow 134.
In certain examples, solids 510 may include drill cuttings. For example, when
drill bit 101 (not shown) cuts segments of earth (e.g., rock) or other
material from
formation 107, a drill cutting may become disposed in circulating fluid to be
carried
to well surface 106 by fluid flow 134. As many drill cuttings are removed from
formation 107 and caused to enter the circulating fluid in wellbore 114,
wellbore 114
may be lengthened.
In certain examples, solids 510 may include LCM solids. Various types of
LCM solids may be added to the circulating fluid before the circulating fluid
enters
drill string 103. LCM solids may facilitate sealing parts of formation 107
that are
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subject to fluid loss due to being weak, porous, and/or fractured. For
example, LCM
solids may help isolate formation 107 from fluids in wellbore 114 by plugging
or
helping plug fractures 136. Similarly, LCM solids may facilitate the creation
of a
filter cake (not shown) along sidewall 118 to further isolate formation 107
from the
fluids circulating in wellbore 114.
FIG. 5 illustrates how solids, including LCM solids, may plug fractures 136
and otherwise isolate formation 107 from wellbore 114. As shown in FIG. 5,
fractures 136 each capture multiple solids 520 from fluid flow 134. As shown,
solids
510 that are captured by fracture 136a may be referred to as solids 520a
(e.g., solids
520a-1 for solids of size 1, solids 520a-2 for solids of size 2, etc.).
Similarly, solids
510 that are captured by fracture 136b may be referred to as solids 520b
(e.g., solids
520b-1 for solids of size 1, solids 520b-2 for solids of size 2, etc.). Solids
510 that are
captured by fracture 136c may be referred to as solids 520c. As shown, because
fracture 136c is relatively narrow, solids 520c may include only solids of
size 1.
Larger solids such as solids 510-2 through 510-5 may not fit in fracture 136c.
Accordingly, larger solids may continue to be carried uphole by fluid flow
134.
Fractures 136a and 136b are wide enough to fit larger solids. For example
solids
520b within fracture 136b include solids 520b-1 of size 1 as well as solids
520b-2 of
size 2. Similarly, solids 520a within fracture 136a include solids 520a-1 of
size 1,
520a-2 of size 2, 520a-3 of size 3, and solids 520a-4 of size 4. Thus,
fracture 136a
may be large enough to capture any size of solid except solids 510-5 of size
5.
As shown in FIG. 5, each of fractures 136 may become substantially plugged
by solids 520 after fluid flow 134 has carried past a sufficient number of
solids 510
past to fill and plug fractures 136. However, as fractures 136 capture solids
520 with
particular physical characteristics, such as solids below a size threshold of
what will
fit in a particular fracture 136, the variety of solids 510 remaining in fluid
flow 134
may be altered. For example, as shown in FIG. 5, a wider assoi _______ tment
of solids 510
may be present in fluid flow 132 after entering drill string 103 than the
assortment
that will emerge from wellbore 114 from fluid flow 134 after circulation.
Specifically, fluid flow 134 may have fewer solids 510 that are relatively
small (e.g.,
solids 510-1, 510-2 and 510-3) because the smaller solids 510 are captured by
fractures 136 and remain in fractures 136 while larger solids (e.g., solids
510-4 and
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510-5) continue with fluid flow 134.
A consistently wide variety of LCM solids may facilitate proper plugging of
fractures as the fractures form and develop. For example, when too few smaller
LCM
solids are disposed in the circulating fluid, the larger LCM solids may fail
to properly
plug fractures because too few LCM solids fit in the fractures. Conversely,
when too
few larger LCM solids are disposed in the circulating fluid, the smaller LCM
solids
may fail to properly plug the fractures because the smaller LCM solids do not
properly accumulate in the fractures (e.g. by becoming stuck due to a tighter
fit).
Accordingly, it may be desirable to maintain a particular mix of LCM solids in
the
circulating fluid so that fractures of various sizes can be plugged quickly
and properly
as hydrocarbon production proceeds. However, maintaining a desired variety of
LCM
solids may present challenges. For example, determining even a rudimentary
inventory of LCM solids emerging from a wellbore may be difficult because of
the
large number and small size of the LCM solids, as well as because of other
solids
(e.g., drill cuttings) intermixed with the LCM solids within the circulating
fluid in
which the LCM solids are disposed. Determining characteristics of fractures in
the
formation may provide a means for determining which LCM solids a formation has
captured and predicting which LCM solids the formation may capture in the
future.
For example, characterizing the fractures of a formation may reveal what sizes
of
LCM solids are being captured by the fractures as well as a desirable mix of
LCM
solids that may be disposed within wellbore 114 at any particular time.
One way to characterize fractures and thereby determine which LCM solids
have been captured by fractures in a wellbore is by use of MEMS devices.
Accordingly, in certain embodiments, solids 510 may include MEMS devices. Just
as
other solids 510 (e.g., LCM solids, drill cuttings, etc.) may vary in size,
shape, and/or
density, MEMS devices included in solids 510 may also include a non-uniform
assortment of MEMS devices varying in size, shape, and/or density, as
illustrated in
FIG. 4. As described in FIG. 4, certain MEMS devices within the non-uniform
assortment may be configured to emulate one or more physical attributes
associated
with particular solids or fluids. For example, MEMS devices within the non-
uniform
assortment may be configured to emulate other solids 510 or fluids disposed in
wellbore 114. By emulating solids 510, MEMS devices may behave similarly or
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identically with the solids they emulate.
When MEMS devices emulating particular physical attributes of an LCM solid
are determined to be captured by fractures, it may be inferred that similar
LCM solids
have also been captured by the fractures. For example, among other types of
solids,
solids 510 may include five sizes of LCM solids with a spherical shape and a
low
density. For example, solids 510 may include 0.5 millimeter (mm) LCM solids, 1
mm
LCM solids, 5 mm LCM solids, 10 mm LCM solids, and 50 mm LCM solids.
Accordingly, solids 510 may also include MEMS devices with a similar spherical
shape and a similar low density in the same five sizes. As solids 510,
including the
five sizes of LCM solids and the MEMS devices emulating the five sizes of LCM
solids, are circulated, certain LCM solids and MEMS devices may be captured by
one
or more fractures 136. For example, in FIG. 5, the five sizes of LCM solids
and
MEMS devices may be shown by solids 510-1 through 510-5. As shown in FIG. 5,
many smaller LCM solids and MEMS devices (e.g., solids 510-1 and 510-2) may be
captured by fractures 136. For example, several solids 520c-1 may be captured
within
fracture 136c, several solids 520b-1 and 520b-2 are captured within fracture
136b, and
several solids 520a-1 and 520a-2 are captured within fracture 136a. Fewer mid-
sized
LCM solids and MEMS devices (e.g., solids 510-3 and 510-4) may be captured by
fractures 136. For example, no solids 510-3 or 510-4 are captured by fractures
136c
or 136b, and only a few are captured by fracture 136a. In FIG. 5, no solids
510-5 may
be captured by any fracture. Accordingly, all of the 50 mm MEMS devices, as
well
as a large portion of the 10 mm and 5 mm MEMS devices may continue circulating
up to well surface 106.
Subsequently, as described in relation to FIG. 2 above, MEMS scanner 212
may scan designators of the subset of MEMS devices emerging from wellbore 114
without being captured by fractures 136. MEMS analysis subsystem 202 may
receive
the designators of the subset and compare the subset with the set of MEMS
devices
that originally entered drill string 103 to identify MEMS devices present in
the set but
missing from the subset. MEMS analysis subsystem 202 may also determine, based
on the MEMS devices identified to be missing from the subset (e.g., the MEMS
devices captured by fractures 136), a size threshold associated with a maximum
size
of the MEMS devices missing from the subset. For example, MEMS analysis
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subsystem 202 may determine that at least one fracture is about 10 mm wide
because
some 10 mm MEMS devices (e.g., solids 320a-4) are missing from the subset.
MEMS analysis subsystem 202 may also infer that there may be additional
smaller
fractures because many 0.1 mm and I mm MEMS devices (e.g., solids 320-1 and
320-
2) are also missing from the subset. MEMS analysis subsystem 202 may also
infer
that there is no fracture in wellbore 114 that exceeds 50 mm in width because
zero or
substantially zero 50 mm MEMS devices (e.g., solids 310-5) may be missing from
the
subset. Accordingly, based on the size threshold of the MEMS devices present
in the
set but missing from the subset, MEMS analysis subsystem 202 may determine
that at
least one fracture is present in wellbore 114 and may determine an approximate
size
of the fracture to be greater than 10 mm and less than 50 mm.
Because the MEMS devices emulating the various sizes and types of LCM
solids may be captured by fractures 136 in a similar or identical manner as
the LCM
solids themselves, MEMS analysis subsystem 202 may also infer information
about
the LCM solids from the subset of MEMS devices detected. For example, when
MEMS analysis subsystem 202 determines that many MEMS devices less than a size
threshold (e.g., 10 mm) have been captured, MEMS analysis subsystem 202 may
infer
that similarly sized LCM solids may have also been captured. Accordingly,
additional LCM solids may be introduced into fluid flow 132 based on the
subset of
MEMS devices and/or the characteristics of the fracture determined by MEMS
analysis subsystem 202. For example, additional LCM solids less than the size
threshold (e.g., smaller than 10 mm) may be introduced into fluid flow 132 to
maintain the desired wide variety of LCM material in the circulating fluid.
In some examples, MEMS analysis subsystem 202 may be able to infer
additional information from the subset of MEMS devices emerging from wellbore
114 in any manner that suits a particular embodiment. For example, in certain
embodiments, designators of MEMS devices included in solids 510 may include
unique serial numbers and/or time stamps known to MEMS analysis subsystem 202.
When MEMS devices having a particular place in a sequence (e.g., as
determinable
by the serial number and/or timestamp of the MEMS devices) are determined to
be
missing from the subset of MEMS devices emerging from wellbore 114, MEMS
analysis subsystem 202 may determine other characteristics about fractures
such as
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approximate locations of the fractures, timing characteristics associated with
the
fractures (e.g., when the fractures were created), whether a fracture is a
breathing
fracture, and other characteristics of the fracture.
"Breathing fractures" may refer to fractures within subterranean formations
that receive circulating fluid when a hydrostatic pressure of circulating
fluid against
the formation exceeds a fracture collapse pressure of the breathing fracture,
and that
give back circulating fluid otherwise. For example, in a breathing fracture,
circulating
fluid may flow back into the formation when the hydrostatic pressure exerted
by the
circulating fluid against the formation is less than the fracture collapse
pressure. A
breathing fracture may be referred to as "open" when hydrostatic pressure is
sufficiently high to cause the breathing fracture to receive circulating
fluid. The
breathing fracture may be referred to as "closed" when the hydrostatic
pressure is
lower and the circulating fluid flows back into the formation. The fracture
collapse
pressure may be related to the equivalent effective density of the circulating
fluid.
The fracture collapse pressure may be determined by taking into account
various
parameters such as the weight of the circulating fluid, the depth of the
fracture, the
pressure drop in the annulus at the depth of the fracture, the characteristics
of the
formation, and other suitable parameters. In some examples, a breathing
fracture may
be open when circulating fluid pumps are engaged and closed when the
circulating
fluid pumps are disengaged.
Breathing fractures may cause problems for subterranean operations in a
similar manner as other types of fractures. However, breathing fractures may
also be
symptomatic of significant risk to the operations in the wellbore. For
example,
although breathing fractures may be difficult to detect and may be of minor
consequence in and of themselves, breathing fractures may lead to more
significant
fractures when left untreated. Accordingly, characterizing breathing fractures
within
the wellbore may provide valuable information for decision making regarding
subterranean operations. For example, early characterization of breathing
fractures
before the breathing fractures develop into larger problems may allow
operators to
take appropriate measures to protect the integrity of the wellbore, the
operations
within the wellbore, the production schedule, and/or the personnel associated
with
production of hydrocarbons in the wellbore. In certain examples, as described
above
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in relation to FIG. 5, operators may attempt to treat the breathing fracture
by plugging
it with appropriate LCM solids based on a characterization of the size of the
fracture
performed using a non-uniform assortment of MEMS devices emulating various LCM
solids.
Like breathing fractures, formation kicks are another undesirable phenomenon
that may occur in a wellbore during subterranean hydrocarbon production.
Formation
kicks may occur when a region of a formation surrounding a wellbore has
greater
pressure than the hydrostatic pressure from the circulating fluid in the
wellbore. The
high pressure region of the formation may be exposed by drilling through or
into the
region, or may develop as pressure increases over time. The symptoms of
formation
kicks may be similar to the symptoms of breathing fractures. Specifically,
both
formation kicks and breathing fractures may expel a volume of fluid into the
wellbore
which eventually is circulated to the well surface. In some examples, a
breathing
fracture may expel a volume of circulating fluid that was previously received
by the
formation into the wellbore. In other examples, a formation kick may expel
natural
subterranean fluids from the formation (e.g., water, hydrocarbon fluids, etc.)
into the
wellbore.
Distinguishing between a breathing fracture and a formation kick may be
difficult because the primary symptom of each phenomenon¨an unexpected volume
of fluid¨may be similar. However, distinguishing between breathing fractures
and
formation kicks may be important because proper treatment of breathing
fractures
may be distinct from proper treatment of formation kicks.
Turning to FIGS. 6A and 6B, referred to collectively as FIG. 6, views of
circulating fluid in a wellbore are illustrated. Specifically, FIG. 6A
illustrates
exemplary solids disposed in a circulating fluid surrounded by a subterranean
formation that includes a breathing fracture. As shown, FIG. 6 illustrates
wellbore
600 and breathing fracture 604 at two different moments in time, t1 and t2.
FIG. 6A
illustrates wellbore 600 at time T = ti. At time ti, sufficient hydrostatic
pressure from
the circulating fluid in wellbore 600 may exist to open breathing fracture
604. For
example, at time ti, circulating fluid pumps at the well surface (not shown)
may be
engaged. Meanwhile, FIG. 6B illustrates wellbore 600 at time T = t2, which may
be
later than time ti. At time t2, the hydrostatic pressure from circulating
fluid in
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wellbore 600 may be insufficient to open breathing fracture 604, and breathing
fracture 604 may thus be closed. For example, at time t2, the circulating
fluid pumps
may be disengaged.
As shown in FIG. 6, circulating fluid is pumped downhole in drill string 103
in
the direction of fluid flow 132. At a downhole point (not shown), the
circulating fluid
may exit drill string 103 (e.g., through nozzles of a drill bit, not shown)
and may flow
in an uphole direction indicated by fluid flow 134. In FIG. 6, subterranean
formation
602 may surround wellbore 600. Formation 602 may include breathing fracture
604.
As discussed above in reference to FIG. 5, various solids including drill
cuttings,
LCM solids, and MEMS devices may be disposed in the circulating fluid flowing
in
wellbore 600. However, whereas FIG. 5 illustrated various types of solids with
various physical characteristics, the only solids shown in FIG. 6 are MEMS
devices.
Specifically, for descriptive clarity in FIG. 6, MEMS devices 610 and 620 are
shown
as being approximately uniform in size, shape, and other physical
characteristics.
However, it is noted that in various embodiments, an assortment of solids not
expressly shown or discussed in reference to FIG. 6 may be disposed in the
circulating fluid of FIG. 6 and may perform similar functions as described in
relation
to FIGS. 3 through 5. Additionally, although not shown in FIG. 6, it is noted
that
MEMS devices 610 and 620 may include a non-uniform assortment of MEMS
devices varying in size, shape, density, and/or other physical parameters in
various
embodiments.
In FIG. 6, MEMS devices 610 and 620 are each labeled with a number. For
example, MEMS devices 620 are labeled with numbers such as 3, 7, 8, 12, and
17.
Similarly, MEMS devices 610 are labeled with numbers such as 51 through 59.
The
number labeled on each MEMS device 620 and 610 may represent a serial number
associated with a designator of each MEMS device. For example, MEMS devices
620 may be machine-scannable to read out designators including respective
serial
numbers: 3, 7, 8, 12, and 17. Each MEMS device 610 and 620 may be referred to
specifically by its serial number. For example, the MEMS device labeled with
serial
number 3 may be referred to as MEMS device 620-3 and the MEMS device labeled
with serial number 51 may be referred to as MEMS device 610-51.
The serial numbers of MEMS devices 610 and 620 may be associated with an
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order and/or a time at which MEMS devices 610 and 620 entered drill string 103
within wellbore 600. For example, MEMS devices 610 and 620 may enter drill
string
103 in the order indicated by the serial numbers such that, of the MEMS
devices
shown in FIG. 6, MEMS device 620-3 entered first, MEMS device 620-7 entered
second, and so on until MEMS device 610-59, which entered last. In the
embodiment
of FIG. 6, other MEMS devices not shown (e.g., MEMS devices with serial
numbers
of 1, 2, 4, 5, 6, 9, etc.) may also enter wellbore 600 in serial number order.
For
example, in the embodiment of FIG. 6, 100 MEMS devices with serial numbers 1
through 100 may have entered wellbore 600 in serial number order, even though
only
particular MEMS devices are shown near breathing fracture 604 at time ti (see
FIG.
6A) and time t2 (see FIG. 6B).
In various embodiments, more or fewer MEMS devices may enter wellbore
600 with any serial numbers that suit a particular embodiment. For example,
serial
numbers may be unique or non-unique. Serial numbers may be in numerical order
or
may be random or out of order. For example, the serial numbers of MEMS devices
610 and 620 in FIG. 6 are shown to enter wellbore 600 in serial number order
for
descriptive clarity. However, in other embodiments, MEMS devices disposed in
circulating fluid may be preprogrammed with serial numbers such that it would
be
impractical or difficult to arrange the MEMS devices to enter wellbore 600 in
serial
number order. In such embodiments, a MEMS scanner (e.g., MEMS scanner 210 in
FIG. 2) may scan the designator of each MEMS device as the MEMS device enters
wellbore 600 and communicate a serial number associated with the designator to
a
MEMS analysis subsystem (e.g., MEMS analysis subsystem 202 in FIG. 2). The
MEMS analysis subsystem may use the serial numbers received from the MEMS
scanner to track the order in which the MEMS devices entered wellbore 600. In
this
way, the order that each MEMS device entered wellbore 600 may be accounted for
irrespective of the actual serial numbers programmed into each MEMS device.
Accordingly, the MEMS analysis subsystem may perform fracture characterization
as
described herein without arranging the MEMS devices to enter wellbore 600 in
any
particular order.
As shown in FIG. 6A, a circulating fluid pump may be engaged at time t1,
generating a hydrostatic pressure of the circulating fluid against formation
602 greater
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than a fracture collapse pressure of breathing fracture 604. Accordingly, as
shown,
breathing fracture 604 may open to receive circulating fluid, including MEMS
devices
620, which are disposed in the circulating fluid. Prior to time t1, certain
MEMS
devices (e.g., MEMS devices having serial numbers 1, 2, 4-6, 9-11, 13-16, and
18-50,
not shown) may have been carried past breathing fracture 604 by fluid flow
134.
Meanwhile, MEMS devices 620 (e.g., MEMS devices 620-3, 620-7, 620-8, 620-12,
and 620-17) may have been captured by breathing fracture 604, as shown. As
breathing fracture 604 fills with circulating fluid, MEMS devices, and/or
other solids
(not shown), MEMS devices 610 may be carried past breathing fracture 604. For
example, at time ti, FIG. 6A illustrates that MEMS devices 610-51 through 610-
59
are near breathing fracture 604. Additionally, MEMS devices with serial
numbers 60
and higher may be downhole in fluid flow 134, in fluid flow 132 within drill
string
103, and/or at the well surface awaiting entrance into wellbore 600.
After time t1, the hydrostatic pressure in wellbore 600 may decrease. For
example, after time ti a circulating fluid pump generating the hydrostatic
pressure
may be shut off or disengaged. Accordingly, sometime after time ti, the
hydrostatic
pressure in wellbore 600 may be no longer be sufficient to continue holding
open
breathing fracture 604. As breathing fracture 604 closes, circulating fluid
may flow
back into formation 602 carrying any solids that may be disposed within the
circulating fluid.
Along with FIG. 6A, FIG. 6B illustrates exemplary solids disposed in a
circulating fluid within a wellbore surrounded by a subterranean formation
that
includes a breathing fracture. Specifically, FIG. 6B illustrates wellbore 600
at time t2,
which may be some time after time t1. As shown in FIG. 6B, breathing fracture
604 is
closed at time t2 and the circulating fluid that breathing fracture 604
captured when it
was open (see FIG. 6A) has flowed back into wellbore 600, recombining MEMS
devices 620 with MEMS devices 610 in fluid flow 134. However, because MEMS
devices 620 were captured out of fluid flow 134 for a period of time, MEMS
devices
620 may be substantially out of order in relation to MEMS devices 610 in fluid
flow
134. Specifically, MEMS devices 620 (e.g., MEMS devices 620-3, 620-7, 620-8,
620-12, and 620-17), which all have serial numbers less than 18, may now be
intermixed in fluid flow 134 with MEMS devices 610 (e.g., MEMS devices 610-56
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through 610-66), which all have serial numbers above 55.
After time t2, each of the MEMS devices 620 and 610 may eventually be
carried by fluid flow 134 to emerge from wellbore 600, where a MEMS scanner
(e.g.,
MEMS scanner 212 in FIG. 2) may scan the designators, including the serial
numbers,
of all of MEMS devices 620 and 610. A MEMS analysis subsystem (e.g., MEMS
analysis subsystem 202 in FIG. 2) may receive the serial numbers and analyze
the
order that MEMS devices 620 and 610 emerged from wellbore 600 after
circulation.
The MEMS analysis subsystem may determine that MEMS devices 620 are
substantially out of order with MEMS devices 610. The MEMS analysis subsystem
may have an order tolerance such that every MEMS device is not expected to
arrive at
the surface in precisely the same order the MEMS device entered wellbore 600.
However, the MEMS analysis subsystem may be configured to detect when MEMS
devices are substantially out of order. For example, the MEMS analysis
subsystem
may ignore MEMS devices that are out of order by less than a maximum number of
MEMS devices (e.g., 20). Thus, if the MEMS device with serial number 11
emerges
from wellbore 600 prior to the MEMS device with serial number 2, the MEMS
analysis subsystem may not determine that the MEMS device with serial number
11 is
substantially out of order. However, when MEMS device 610-56 emerges from
wellbore 600 prior to MEMS device 620-8, the MEMS analysis subsystem may
determine that MEMS device 620-8 is substantially out of order. In various
embodiments, a maximum number of MEMS devices to be out of order may not be
used or may be less than or greater than 20 as suits a particular embodiment.
Similarly, the MEMS analysis subsystem may ignore MEMS devices that are
out of order when only a small number of MEMS devices are out of order (e.g.,
less
than 4). Thus, if only two MEMS devices are detected to be more than 20 MEMS
devices out of order, the MEMS analysis subsystem may not determine that the
two
MEMS devices are substantially out of order. However, when all five MEMS
devices
620 are more than 20 MEMS devices out of order, the MEMS analysis subsystem
may determine that MEMS devices 620 are substantially out of order. In various
embodiments, the number of MEMS devices to be out of order may be less than or
greater than 4 as suits a particular embodiment. Additionally, in various
embodiments,
the MEMS analysis subsystem may analyze more or fewer characteristics of the
order
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of MEMS devices in determining whether particular MEMS devices are
substantially
out of order.
Once MEMS devices are determined to be substantially out of order, the
MEMS analysis subsystem may determine a characteristic of a fracture based on
the
substantially out of order MEMS devices. For example, MEMS devices 620 may be
determined to be substantially out of order in the example of FIG. 6 because
five
MEMS devices 620 are each out of order by more than 20 MEMS devices.
Accordingly, the MEMS analysis subsystem analyzing MEMs devices 620 and 610
may determine that breathing fracture 604 is present in wellbore 600.
Specifically,
the MEMS analysis subsystem may infer that breathing fracture 604 captured
MEMS
devices 620 for a period of time and then expelled them back into wellbore
600, thus
causing MEMS devices 620 to become substantially out of order with MEMS
devices
610. The MEMS analysis subsystem may further determine an approximate size of
breathing fracture 604 based on the number, size, shape, and/or density of
MEMS
devices 620, using techniques described above with reference to FIG. 5. The
MEMS
analysis subsystem may further determine an approximate location of breathing
fracture 604 within wellbore 600 based on designators of MEMS devices 610 that
are
intermixed with substantially out of order MEMS devices 620. For example, the
MEMS analysis subsystem may track an approximate depth that MEMS devices 610
are expected to have at various times. Thus, the MEMS analysis subsystem may
be
able to determine an approximate depth of MEMS devices 610-56 through 610-66
when circulating fluid pumps are disengaged. When MEMS devices 620 are then
determined to be intermingled with MEMS devices 610-56 through 610-66, MEMS
analysis subsystem may determine that a breathing fracture is present at the
approximate depth of MEMS devices 610 at the time the circulating fluid pumps
were
disengaged.
The MEMS analysis subsystem may also help distinguish breathing fractures
from formation kicks. While both breathing fractures and formation kicks
manifest
themselves by an influx of additional fluid in wellbore 600, only breathing
fractures
may manifest themselves with a simultaneous influx of substantially out of
order
MEMS devices into wellbore 600. Accordingly, in certain embodiments, a MEMS
analysis subsystem may be configured to distinguish whether superfluous fluid
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associated with ongoing subterranean operations in wellbore 600 is caused by a
breathing fracture or a formation kick by determining whether the superfluous
fluid is
accompanied by substantially out of order MEMS devices.
Embodiments disclosed herein include:
A. An apparatus
including a microelectromechanical system (MEMS)
device with an associated multi-unit designator, and a capsule encapsulating
the
MEMS device and adapted for use in subterranean operations, wherein a first
unit of
the multi-unit designator is machine-scannable from the MEMS device while the
MEMS device is encapsulated within the capsule.
B. A method
including circulating a volume of circulating fluid through a
wellbore surrounded by a subterranean formation, the circulating fluid
including a
microelectromechanical system (MEMS) device encapsulated by a capsule adapted
for use in subterranean operations, identifying the MEMS device in response to
circulating the volume of circulating fluid, and determining a characteristic
of the
subterranean formation based on identifying the MEMS device.
The embodiments A and B may have one or more of the following additional
elements in any combination: Element 1: wherein the MEMS device is passive.
Element 2: wherein the multi-unit designator includes a serial number. Element
3:
wherein each unit of the multi-unit designator is an individual digit or
character of the
serial number. Element 4: wherein the capsule includes a reactive part that
reacts to a
characteristic of a subterranean formation and a nonreactive part that does
not react to
the characteristic. Element 5: wherein the multi-unit designator is
magnetically
encoded along a length of the MEMS device, the magnetically encoded length of
the
MEMS device being partially encapsulated by the reactive part and partially
encapsulated by the nonreactive part. Element 6: wherein the reactive part of
the
capsule reacts to the characteristic by degrading to expose a portion of the
MEMS
device, the exposed portion being associated with the reactive part such that
the
exposed portion is no longer encapsulated by the capsule in response to the
degrading
of the reactive part. Element 7: wherein a second unit of the multi-unit
designator
associated with the exposed portion of the MEMS device is not machine-
scannable
from the MEMS device due to the reaction of the reactive part of the capsule
to the
characteristic. Element 8: wherein at least part of the exposed portion of the
MEMS
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device detaches from the MEMS device in response to no longer being
encapsulated.
Element 9: wherein the characteristic of the subterranean formation is a
temperature.
Element 10: wherein the characteristic of the subterranean formation is
nuclear
radiation. Element 11: wherein the characteristic of the subterranean
formation is
associated with chemical properties of matter within the formation. Element
12:
wherein the capsule emulates a physical attribute associated with at least one
of a
fluid disposed downhole during the subterranean operations and a solid
disposed
within the fluid. Element 13: wherein the solid disposed within the fluid is a
drill
cutting. Element 14: wherein the solid disposed within the fluid is a lost-
circulation
material (LCM) solid. Element 15: wherein the physical attribute is a size
associated
with the solid. Element 16: wherein the physical attribute is a shape
associated with
the solid. Element 17: wherein the physical attribute is an aspect ratio
associated with
the solid. Element 18: wherein the physical attribute is a density associated
with the
fluid. Element 19: wherein the capsule is constructed of a material selected
to
emulate the density associated with the fluid, the material being selected
from a group
consisting of: ceramic, polymer, metal, and glass. Element 20: wherein the
MEMS
device is identified by a MEMS scanner located at a position on a well surface
above
the subterranean formation where the volume of circulating fluid emerges from
the
wellbore after circulating through the wellbore. Element 21: wherein the MEMS
device is identified by a MEMS scanner located along the wellbore while the
MEMS
device is carried by the volume of circulating fluid circulating through the
wellbore.
Element 22: wherein the MEMS scanner is located along a drill string within
the
wellbore. Element 23: a method further inluding identifying the MEMS device
prior
to the circulating of the volume of circulating fluid within the wellbore, and
determining that the MEMS device reacted to a characteristic of the
subterranean
formation based on a change detected between the identifying of the MEMS
device
prior to the circulating and the identifying of the MEMS device in response to
the
circulating. Element 24: wherein, the MEMS device is associated with a multi-
unit
designator having units that are machine-scannable from the MEMS device while
the
MEMS device is encapsulated within the capsule, and the change detected is
that one
or more units of the multi-unit designator are machine-scannable at the
identifying of
the MEMS device prior to the circulating but are not machine-scannable at the
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identifying of the MEMS device in response to the circulating. Element 25:
wherein
the characteristic of the subterranean formation relates to at least one of a
temperature
of the subterranean formation, nuclear radiation within the subterranean
formation,
and chemical properties of matter within the formation.
Systems and methods for formation characterization in a subterranean
formation are disclosed herein. A set of MEMS devices may be disposed in a
circulating fluid. Each MEMS device in the set may have a machine-scannable
designator. A MEMS scanner may be configured to scan the designator of a MEMS
device in response to circulation of the circulating fluid in a wellbore
surrounded by
the formation. A MEMS analysis subsystem communicatively coupled with the
MEMS scanner may store the designator of each MEMS device in the set, detect a
subset of MEMS devices by receiving the designators of MEMS devices from the
MEMS scanner, and determine a characteristic of the formation based on the
subset of
MEMS devices.
Although the present disclosure and its advantages have been described in
detail, it should be understood that various changes, substitutions and
alterations can
be made herein without departing from the spirit and scope of the disclosure
as
defined by the following claims. For example, embodiments relating to
detecting
fractures within a formation by detecting MEMS devices missing from a subset
of
MEMS devices may be combined with embodiments relating to detecting that MEMS
devices have been affected by characteristics of the formation because one or
more
units of the designators is lost. Similarly, these embodiments may be combined
with
embodiments relating to detecting out-of-order MEMS devices that indicate
breathing
fractures within a formation and/or other embodiments described herein.
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