Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02397916 2002-07-18
WO 01/53855 PCT/USO1/01729
RESISTIVITY AND DIELECTRIC CONSTANT WELL CORE
MEASUREMENT SYSTEM FOR MEASUREMENT WHILE DRILLING AND
LABORATORY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates generally to measurement-while-drilling tools
and specifically to resistivity and dielectric constant measuring tools.
Background and Description of the Prior Art
Drilling oil wells is an extremely expensive undertaking. The more
confidence that a particular formation will be productive the easier it is for
a drilling
company to take the financial risks associated with the drilling operation.
Technology has progressed to allow acquisition of informative data to
determine the
viability of a well. Two current methods of formation evaluation are the down
hole
measurement while drilling (MWD) method and core sample method. In the MV~ID
method, down hole instrumentation measures specified parameters of the
formation
surrounding the drill stem. In the core sample method, a special drill bit is
used that
allows the retrieval of a section of formation for evaluation by surface
measuring
devices. In some cases the instrumentation for MWD is used down hole while
also
drilling a core sample to measure the properties of the surrounding formation
for later
comparison to core sample data recorded on the surface.
A technique used for evaluating formations surrounding an earth borehole is
to measure the resistivity and dielectric constant of the formation. Porous
formations
with high resistivity and dielectric constant generally indicate the presence
of
hydrocarbons while porous formations with low resistivity and dielectric
constant are
normally water saturated and contain no hydrocarbons.
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Typically, tools used to measure these formation characteristics during
drilling
use a wave propagation tool to measure phase delay and attenuation of
electromagnetic waves propagating in the formation over a predefined interval.
Such
devices are described in detail in U.S. Pat. No. 3,551,797 and U.S. Pat. No.
4,968,940. All conventional devices for use during drilling use antennas on
the
outside of a drill collar to transmit or receive the signal. The general
direction of
advancement is always toward higher data accuracy with higher reliability.
The methods for evaluation of core samples for geophysical parameters which
are of interest to the person skilled in the art in the study of oil wells
being drilled
utilize, for example, the natural radioactivity of the core sample, the
absorption of a
known radiation emitted by a known source arranged in proximity to the core
sample,
and the value of the liquid saturation of the core sample (which value is
measured by
induction).
To date, this type of parameter has been measured and/or detected by first
retrieving a core sample and then arranging the core sample which has been
withdrawn from the well substantially horizontally on the ground and by moving
a
carriage equipped with the measuring instrument or instruments manually along
the
core sample.
Parameters of the abovementioned type can be influenced by the environment
of the core sample at the time of measurement, or else similar parameters
originating
from the environment may be added to the corresponding parameters of the core
sample during the measurement taken therefrom. Thus, when the core sample is
arranged horizontally, since one of its sides is closer to the ground than the
other, this
difference in distance may affect the result of the measurement, or else the
ground
may influence the instruments because of its proximity, this being
increasingly so
since this proximity is asymmetrical relative to the mass of the core sample
as a
whole. Overall, lack of accessibility to the core sample makes it difficult to
optimize
the measurement.
The present invention combines the advantages of core sampling with the
advantages
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of MWD to provide an apparatus and method to determine the characteristics of
a
core sample while the sample is in its original environment and while in its
original
orientation relative to the surrounding formation.
SUMMARY OF THE INVENTION
It is a general objective of the present invention to provide an improved
measurement-while-drilling (MWD) tool and method for obtaining highly accurate
data regarding resistivity and dielectric constant parameters of solids,
liquids or a
combination thereof, whether flowing or stationary, while core drilling a well
or in
a laboratory.
This objective can be met with an in-situ core sample measuring
embodiment wherein a core sample is measured within the core sample cavity of
a
drill stem by situating a receiving antenna, a plurality of transmitters and a
plurality of receivers in a core drill stem such that the electromagnetic
waves
propagate through the core sample within the core sample cavity rather than
the
formation surrounding the drill stem.
This objective may also be met in a laboratory environment with a
cylindrical cavity containing the sample to be measured. The cylindrical
cavity
being equipped with electromagnet wave propagation instrumentation as
mentioned in the above drilling system. Other features and advantages will
become
clear in the following detailed description.
Accordingly, in one aspect of the present invention there is provided an
apparatus for measuring a parameter of interest of a material in a
subterranean
formation, the apparatus comprising:
(a) a cylindrical enclosure for enclosing the material;
(b) at least one transmitter having an antenna on the inside of the
cylindrical
CA 02397916 2005-12-21
enclosure for propagating electromagnetic radiation in the material at at
least two
frequencies;
(c) at least one receiver having an antenna on the inside of the cylindrical
enclosure axially displaced from the at least one transmitter for measuring
electromagnetic radiation in the material at each of the at least two
frequencies, the
measurements being indicative of the parameter of interest;
(d) a core bit operatively coupled to the cylindrical enclosure for separating
the
material from the subterranean formation; and
(e) a drilling tubular for conveying the cylindrical enclosure into a borehole
in
the subterranean formation wherein the drilling tubular is selected from the
group
consisting of (A) a drill string and (B) a coiled tubing.
According to another aspect of the present invention there is provided a
method for determining a parameter of interest of a material comprising:
(a) operatively coupling a core bit to a cylindrical enclosure;
(b) conveying the cylindrical enclosure into a borehole in a subterranean
formation on a drilling tubular selected from the group consisting of (A) a
drill
string and (B) a coiled tubing;
(c) operating the core bit for separating the material from the subterranean
formation;
(d) enclosing the material in the cylindrical enclosure;
(e) propagating electromagnetic radiation in the material using at least one
transmitter antenna on the inside of the cylindrical enclosure transmitting at
least
two frequencies; and
(f) measuring with at least one receiver antenna on the inside of the
cylindrical
enclosure axially disposed from the at least one transmitter the propagated
electromagnetic radiation in the material at each of the frequencies, the
measurements indicative of the parameter of interest.
3a
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BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described more fully
with reference to the accompanying drawings in which:
Figure 1 depicts a drilling system.
Figure 2A prior art shows a conventional measurement system simplified
diagram.
Figure 2B is a simplified diagram of the present invention.
Figure 3A is a detailed view of the data acquisition portion of the present
invention
with a cutaway showing a sample contained therein.
3b
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Figure 3B is an enlarged cross sectional view of an aperture in the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a highly accurate; fully compensated, high spatial
resolution, wave propagation system for measuring dielectric constant and
resistivity
of fluids or solids in a cylindrical enclosure. The system can be used for
measuring
well core characteristics in-situ or in a laboratory, and can also be used for
measuring
fluids, solids or combination thereof either during flow or stationary inside
the
cylindrical cavity. Systematic unknown variables which affect measurement have
led
to inaccuracies in other resistivity and dielectric constant measurement
systems.
~ne embodiment of the present invention relies on waves propagated from
transmitters spaced symmetrically above and below two spaced receivers which
conununicate electromagnetically via slots on the inner periphery of a
cylindrical
structure.
Referencing Fig. 1, an overall simultaneous drilling and logging system that
incorporates an electromagnetic wave propagation resistivity and dielectric
constant
measurement system according to this invention will now be described in
greater
detail.
A well 1 is being drilled into the earth under control of surface equipment
including a rotary drilling rig 3. In accordance with a conventional
arrangement, rig 3
includes a derrick 5, derrick floor 7, draw works 9, hook 11, kelly joint I5,
rotary
table 17, and drill string 19 that includes drill pipe 21 secured to the lower
end of
kelly joint 15 and to the upper end of a section of drill collars including an
upper drill
collar 23, an intermediate drill collar (not separately shown), and a lower
drill collar
measurement tubular 25 immediately below the intermediate sub. A drill bit 26
is
carried by the lower end of measurement tubular 25. During well drilling
operations
the drill bit will be a conventional bit when the main purpose is to reach a
desired
depth. The conventional drill bit will be replaced by a coring bit when core
samples
are desired. The purpose of the core bit is to retain within the drill string
a sample of
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the borehole called a core sample. The core sample is typically brought to the
surface
for testing and analysis to determine the characteristics of the formation at
the depth
from which the core sample was taken. It will be explained later in this
description
the relationship to current drilling measurements systems, core measurement
systems
and the present invention.
Drilling fluid, or mud as it is commonly called, is circulated from a mud pit
27
through a mud pump 29, past a desurger 31, through a mud supply line 33, and
into
swivel 13. The drilling mud flows down through the kelly joint 15 and an axial
central bore in the drill string, and through jets (not shown) in the lower
face of the
drill bit. The drilling mud flows back up through the annular space between
the outer
surface of the drill string and the inner surface of the borehole to be
circulated to the
surface where it is returned to the mud pit through a mud return line 35. A
shaker
screen (not shown) separates formation cuttings from the drilling mud before
the mud
is returned to the mud pit.
The overall system in Fig. 1 uses mud pulse telemetry techniques to
communicate data from down hole to the surface while drilling operations take
place.
To receive data at the surface, there is a transducer 37 in mud supply line
33. This
transducer generates electrical signals in response to drilling mud pressure
variations,
and the electrical signals are transmitted by a surface conductor 39 to a
surface
electronic data processing system 41.
Mud pulse telemetry techniques provide for communicating data to the surface
about numerous down hole conditions sensed by well logging transducers or
measurement systems that ordinarily are located on and within the drill collar
nearest
the drill bit. The mud pulses that define the data are produced by equipment
within
the intermediate sub. Such equipment typically comprises a pressure pulse
generator
operating under control of electronics contained within an instrument housing
to
allow drilling mud to vent through an orifice extending through the logging
collar
wall. Each time the pressure pulse generator causes such venting, a negative
pressure
pulse is transmitted to be received by surface transducer 37. An alternative
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conventional arrangement generates and transmits positive pressure pulses.
The circulating drilling mud provides a source of energy for a turbine-driven
generator sub-assembly located in the intermediate sub, and the turbine-driven
generator sub-assembly generates electrical power for the pressure pulse
generator
and for various circuits including forming part of the preferred embodiment of
this
invention. As an alternative or supplemental source of electrical power,
batteries may
be provided, particularly as a backup for the turbine-powered generator.
In general, previous MWD systems measure the formation surrounding the
drill stem as shown in Fig. 2A. The measurement of surrounding formation
parameters is accomplished by having electromagnetic waves transmitted
alternately
from transmitters 43 and 49. The waves pass through the surrounding formation
and
are received by receivers 45 and 47. Contrast this conventional measurement
with the
simplified diagram of the measuring system of the present invention shown in
Fig.
2~. For an MWD embodiment, the present invention can be utilized down hole
conveyed on a tool such as a drill string or a coiled tubing. Transmitters 51
and 57
pass electromagnetic fields through a core sample 50 and the fields are picked
up by
receivers 53 and 55. Such a symmetric arrangement of transmitters about the
receivers makes it possible to fully compensate for any linear changes to the
measurement system. U.S. Patent 5,811,973 issued to Meyer, Jr. and having the
same
assignee as the present invention discloses a propagation resistivity
measurement-
while-drilling system used to determine the resistivity (or conductivity) of
the
connate formation fluid, the dielectric constant of the dry rock matrix, and
the water
filled porosity of the formation. One or more transmitter- receiver pairs are
utilized
with the transmitter component of the transmitter- receiver pairs operating at
a
plurality of frequencies. Water filled porosity measurements can be combined
with an
independent measurement which responds to the total fluid porosity of the
formation
to obtain a measure of formation hydrocarbon saturation in fresh or saline
connate
water environments. The contents of U.S. Patent 5,811,973 are fully
incorporated
here by reference.
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Refer now to Fig. 3A which shows the data acquisition portion of the
preferred embodiment of the present invention in detail. A cylindrical
enclosure 59,
which may be a modified core barrel, contains a liquid, solid, gas or
combination
sample 61, either flowing or stationary. The sample in the case of the MWD
embodiment is a core sample. Transmitter T1 63 generates an electromagnetic
wave
to be passed through sample 61 and received by receivers R1 65 and R2 68, The
wave is propagated and received via antennas 64 and 66 respectively. In an
alternating fashion, transmitter T2 69 generates an electromagnetic wave to be
passed
through sample 61 and received by receivers Rl 65 and R2 68. The waves from T1
and T2 are propagated and received via antennas 70 and 68 respectively. The
transmitters are fixed within the cylindrical enclosure 59 about the inner
surface. A
plurality of apertures 60 (shown for T1 only) are provided for each
transmitting
antenna.
In Fig. 3B, an enlarged aperture cross section is shown which is substantially
similar to all other apertures in the preferred embodiment. An electromagnetic
shielding material 73 such as a soft ferrite is positioned within each
aperture for
protecting the cylindrical enclosure from the electromagnetic radiation.
Toward the
inner surface, antenna wire 64 is fixed in said apertures with and a potting
material 71
which also provides protection for said antenna wire. In a preferred
embodiment, the
potting material is an epoxy resin.
In an alternate embodiment of the invention (not shown) the transmitter
antenna is set in a circumferential recess on the inside of the cylinder. This
embodiment is structurally weaker than the slotted design of Fig. 3A-3B.
Data recorded by the receivers can be either transmitted in real time to the
surface or alternately can be recorded with recording instrumentation down
hole (not
shown) for later retrieval. For the real time data transmission embodiment,
signals
from the receivers are transmitted to the surface by a transmission path,
transferred to
a central processing unit (CPU) for processing. The processed data comprising
measures of the parameters of interest, such as an amplitude resistivity or a
phase
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resistivity, are correlated with depths from a drill collar depth indicator
(not shown),
and an output to a recorder which displays the computed parameters of interest
as a
function of depth at which the input measurements were made. An alternate
embodiment comprises a processor unit (not shown) mounted within the drill
collar
23 to perform data processing down hole. In order to most effectively utilize
memory
capacity, it is often desirable to process measured'data down hole and store
processed
results rather than the more voluminous measured data.
It should be understood that the invention is in no way limited to the
described
embodiments, and that many changes may be made to these embodiments without
departing from the scope of the present invention. Other embodiments would be
obvious to those versed in the arts to which the invention pertains.
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