Note: Descriptions are shown in the official language in which they were submitted.
CA 02461995 2004-03-29
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IN-SITU HEAVY-OIL RESERVOIR EVALUATION WITH ARTIFICIAL
TEMPERATURE ELEVATION
BACKGROUND OF THE INVENTION
Field of the Invention
[00011 The invention is in the field of wellbore logging devices.
Specifically, the
invention is a method of heating the rock formation to improve the quality of
data about
rock formations in nuclear magnetic resonance techniques for determining
relaxation
rates, loss tangent measurements, or in sampling of formation fluids as is
done with a
fluid sampling device. A suitable fluid sampling device is that used by Baker
Hughes in
conjunction with services provided under the mark RCI SM for formation fluid
testing.
This includes pressure, temperature, resistivity, capacitance and NMR sensors.
Description of the Related Art
[00021 Almost all the current well-logging instruments are designed to detect
the in-situ
fluid and/or formation properties without deliberately altering the
environmental states,
such as temperature, pressure, etc, of the formation and fluids. In principle,
keeping the
formation and fluids in their native state is a desirable choice in normal
situations.
However, because a tool is more sensitive to operation under certain
conditions, there are
situations where the quality of the measurements will improve if one changes
the
environmental state of the formation and fluids. As long as the modification
does not
create adverse effects on the subject formation and fluids, and as long as the
change of
environment is reversible after the means of modification is removed,
measurements
taken at the modified state are also valid, and experiments can be designed to
be taken at
the more favorable, altered state of the formation. This invention disclosure
is about
designing a tool which changes the environment and makes subsequent
measurements,
resulting in a more effective characterization of formation properties.
Moreover, certain
practices such as the heat produced by drilling change the environment
temporarily. If an
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instrument response is more sensitive at a higher temperature, it will be
desirable to
measure the properties before the drilling induced heat is dissipated. It may
also be
beneficial to make measurements at different temperatures.
[0003] Many petroleum reservoirs in Canada, Venezuela, China, and other
countries
contain highly viscous oils. Most of the heavy-oil reservoirs are relatively
shallow
subsurface ones, where the formation water is often fresh, i.e., low in
salinity. The lack
of conductivity contrast between fresh water and hydrocarbon makes it
difficult to
quantify hydrocarbon saturations using the resistivity-based and induction-
based logging
techniques.
[0004] NMR and dielectric-based techniques are fundamentally different in the
identification of fluid types and quantification of saturations; thus, they
are
complementary to resistivity-based technique. However, heavy oils present
challenges in
current NMR logging techniques. The state-of-art NMR logging tool can
distinguish
water (wetting phase) and hydrocarbon (non-wetting phase) only if their
corresponding
intrinsic and/or apparent relaxation times pose a significant contrast between
the two
types of reservoir fluids.
[0005] NMR responses are different, depending on whether the reservoir fluids
are inside
porous rocks or outside. For bulk, liquid-phase fluids, NMR response depends
on
viscosity and temperature:
AT
T bulk orT2butk - 7,0 , Eq. (1)
where A is a fluid-type dependent quantity and differs by a factor of about 2-
3 between
oil and water, T and To are the absolute temperatures in Kelvin at reservoir
and ambient
conditions, respectively, and rl is the viscosity in cP. For water at room
temperature, rl
1 cP. On the other hand, heavy oil viscosity is typically two (or more) orders
of
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magnitude higher than that of water in a same temperature.
[0006] Although the bulk fluid relaxation time contrast appears useful in
distinguishing
heavy oil from bulk water, it may not be so useful if the fluids are inside
porous rocks. In
a rock, one must take into account additional relaxation mechanism arising
from the
interaction between pore surface and fluids in the pore:
T' Tbu S
rk+pV
S Eq. (2)
T2TZbulk+AV
where S/V is the pore-surface-to-pore-volume ratio and p is the surface
relaxivity which
depends strongly on the wetting characteristics between the fluid and surface
of pores.
Depending on how large the relaxivity value, p, is, the apparent relaxation
times could be
either dominated by the bulk (1St term in eq. (2)) or surface (2nd term in eq.
(2)) relaxation
rate. For the majority of reservoirs, water is the wetting phase and oil is
the non-wetting
one. In this case, the apparent relaxation time of water is dominated by the
surface
relaxation mechanism, resulting in a much faster apparent relaxation decay
than its bulk
relaxation produces. Because the surface relaxation time term depends on S/V,
the
apparent relaxation time is even shorter for smaller sized pores and clays.
The water in
the smaller pores and clays often associates with water that is irreducible,
often known as
BVI (Bound Volume Irreducible) and CBW (Clay Bound Water). Although the
mechanism for shortening the apparent relaxation times are different for heavy
oil and
CBW and BVI water, the result is that they overlap each other, and it is often
difficult to
separate heavy oil from these irreducible water by the difference of their
relaxation times.
[0007] For most viscous oils, the intrinsic T2 is too short for most NMR
logging tools to
detect. The failure to detect these fastest decaying T2 components results in
an
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underestimation of the porosity of the oil-bearing formation. As can be seen
from eq.
(1), the relaxation times of oils are proportional to temperature. The
viscosity, on the
other hand, decreases with temperature. Thus, the relaxation time increases
with
temperature in the rate higher than linear temperature dependence. As most of
the heavy
oil reservoirs are shallow, the reservoir temperature is low. For example, a
significant
amount of heavy oil such as the Athabasca tar sands of Canada and the tar
deposits of the
Orinoco delta in Venezuela occur at shallow depths. For those reservoirs,
underestimation of porosity for the viscous oil sands is highly likely.
[0008] Raising temperature can increase relaxation time T2, making the
otherwise
undetected viscous components detectable, thus rectifying the porosity
underestimation
problem. On the other hand, the relaxation time of the wetting fluid phase,
water, is
dominated by surface relaxation, which is much less sensitive to temperature
change.
Therefore, the shift of T2 towards the longer time alleviates the problem of
identifying
and quantification of heavy oil saturation from faster relaxing BVI and CBW
components.
SUMMARY OF THE INVENTION
[0009] The present invention is a method of determining a parameter of
interest of an
earth formation or a fluid therein at two different times when the temperature
and the
parameter of interest are different. When the formation fluid includes heavy
oil and
water, NMR devices have trouble distinguishing between heavy oil and bound
water in
the formation. By heating the formation (actively or passively), the
temperature is
changed. At elevated temperatures, the transverse relaxation time of heavy oil
can be
distinguished from that of in-situ water.
[0010] Because of the temperature gradient produced in the vicinity of the
borehole by
heating, use of a multiple frequency NMR device which detects signals at
different
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CA 02461995 2009-11-09
depths from borehole walls for each frequency produces a profile of T2
spectra; this is
because the shift of oil relaxation-time components becomes a function of
depth of
investigation.
[0011] Another property that is temperature dependent is the dielectric
constant. The loss
tangent for water shows a significant temperature and frequency dependence and
the
dielectric contrast between hydrocarbon and water can be used to aid the
discernment of
oil and water saturations. Dielectric tools operate at quite different
frequency bands than
resistivity tools. A measure of the loss tangent shows a wide range of
frequencies. For
example, one measurement might be taken at 900kHz while another is taken at
2.4 GHz.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. la is a graph of relaxation times, T2, for crude oil measured with
three
different TE values (0.5, 1.2, 2.4 ms) at 30 C
FIG. lb is a graph of relaxation time, T2, for crude oil measured with three
different TE
values (0.5, 1.2, 2.4 ms) at 75 C.
FIG. 2a is a graph of relaxation time, T2, for crude oil measured at four
different
temperatures (30C, 45C, 60C, 75C) at a constant value of TE = 0.5 ms.
FIG. 2b is a graph of relaxation time, T2, for crude oil measured at four
different
temperatures (30C, 45C, 60C, 75C) at a constant value of TE = 1. 2 ms.
Fig. 3 shows an exemplary logging tool conveyed into a borehole.
DESCRIPTION OF PREFERRED EMBODIMENT
[0013] The present invention is an apparatus and a method that varies the
temperature of
the rock formation within a confined, local region adjacent to a borehole
wall. Any one
of many known devices for NMR measurements may be adapted for the present
invention. For example, when making measurements while drilling, a
modification of an
apparatus such as that disclosed in US Patent 6,247, 542 to Kruspe et al, may
be used.
When making NMR measurements with a. wireline logging tool, a suitable
apparatus is a
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CA 02461995 2009-11-09
modification of the device shown in US Patent 5,712, 566 to Taicher et al.
These
particular patents have been cited only as examples of devices that may be
modified in a
straightforward manner as described below, and the present invention may be a
modification of any suitable NMR logging device. In particular, for efficiency
of heating,
it is desirable to use a tool with a small- apertured NMR sensor. A feature
that is
common to all such suitable devices is a permanent magnet to provide a static
magnetic
field for polarizing spins of nuclei in a formation and an RF assembly for
producing a
pulsed RF field in the formation for excitation and detection of nuclear spin
magnetic
moments.
[0014] Separate embodiments of the invention are comprised of either active or
passive
mechanisms for heating the local volume of formation surrounding the borehole.
Possible modifications of a basic NMR logging apparatus include a microwave
heater
proximate to the NMR assembly for heating the formation by irradiation with
microwaves, or an inductive heating apparatus for heating the formation. For a
very
localized and small NMR sensor, another possible way of heating is by firing
bullets into
formation.
[0015] Passive methods include using the action of the drill tool, which
produces heat,
mainly from friction, to raise the local temperature in the rock formation. In
current
drilling processes, the dissipation of heat is hastened by effectively
circulating the
drilling mud. This cooler mud flows through the drill string and is injected
on the drill
bits; the wasted, hotter mud is brought out through the wellbore. The
temperature of
incoming circulating mud is lower than the formation temperature. If the
circulation is
effective, the temperature of the outgoing mud is higher than the incoming
mud.
However, for deep wells, the formation temperature may be still higher than
the outgoing
mud temperature, resulting in cooling the near borehole formation. For
instance, in
average Gulf of Mexico wells, the circulation bottom hole temperature (BHT)
may be
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about 90 F above static BHT for depths over 10,000 ft.
[0016] However, for shallow wells, where most of the world's heavy oil
reserves exist,
the circulation BHT is close to static BHT. Therefore, if the mud circulation
rate is
controlled such that the heat is dissipated sufficiently slowly, the
circulated mud in the
wellbore actually heats the formation, NMR measurements may be taken at the
passively
heated state. Such temperature control may be achieved by controlling the
amount of
thinning and/or gelling agents in the mud. Although it is desirable to operate
the in a
relatively cool state, due to the fact that the environment temperature for a
shallow well
is low (-40 C), raising the temperature by 30 - 40 C will not significantly
degrade the
drilling operation. Although thermal conductivity of the formation is not
high, it is still
suitable for the present invention since NMR measurements have a shallow-depth
of
investigation. To make use of passive heating, the NMR sensor is positioned
close to the
drillbit and measurements are made before the heat produced by drilling is
substantially
dissipated by drilling mud. Furthermore, additional measurements may be done
at the
equilibrium reservoir temperature, which may be accomplished on another trip
using the
same logging device.
[0017] In another embodiment using passive methods, a refrigerating device is
used to
cool mud that has been heated by the drilling process and the waste heat from
the
refrigerating device is transferred to a heat sink for heating the formation
near an NMR
sensor.
[0018] In another embodiment, the mud is heated from the surface mud pit and
the
heated mud is circulated into the formation to raise the temperature near the
wellbore.
This method is practical for wells that are planned to use a geothermal source
for heating
the formation for recovery from viscous oil formations.
[0019] In one embodiment of the invention, a microwave device transfers
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electromagnetic energy from a microwave source to the formation, where the
energy
dissipates as heat. Microwave energy is generated in a frequency that does not
change
the chemical bonds in the organic constituency of crude oil. At a preferred
frequency of
up to 2,450 MHz, microwave energy leaves the chemical structures of the oil
intact
because there is no ionization, yet it creates molecular motion in the form of
translation
motion of the molecules and rotation of the dipoles.
[0020] The efficiency of the microwave absorption process is determined by
several
elements, including the size of the intended volume and dielectric losses due
to both ionic
conduction and dipolar rotation of the material in the formation rock and
fluids. These
individual dielectric loss rates are generally temperature-dependent but to
different
degrees. The loss due to dipolar rotation decreases with increasing
temperature, while
loss due to ionic conduction increases with increasing temperature. Composite
loss rates
are therefore dependent on the dominant loss mechanism within the formation.
As an
example, for low-temperature wells, the dipolar rotation mechanism is usually
the
dominant mechanism. In this case, the heating time depends on dielectric
relaxation
time.
[0021] For purposes of this invention, the rock formation outside a borehole
is modeled
as a dielectric medium with infinite extent. Hence, there are no boundaries
that might
produce a reflecting wave. In the embodiment using microwaves, as energy
progresses
into the medium, its amplitude diminishes owing to the absorption of power and
conversion to heat. The penetration depth, defined as the depth into the
formation at
which the power flux has fallen to l/e of its entry point value, is given by
the formula
A0 1 e
Dp 2J ~ 2s' j[i+ IE,1J2 2/-r6 "
where 20 is the incident wavelength of the source, E' is the relative
dielectric constant of
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the rock formation and E" is the relative dielectric loss factor.
[0022] The efficacy of temperature increase in the sensitive volume depends on
the
penetration of the microwave energy into the rock formation. Penetration depth
depends
on the operating microwave frequency and is different for rock matrices and
types of
fluids. Therefore, in rock formations, penetration depth depends on porosity
and
saturation. As an example, the microwave heating device can be operated at a
frequency
of 2,450 MHz and X = 12.24 cm at a temperature of 25 C. Under these
conditions, the
measured penetration depths of the energy into corn oil, water, mica, and
sandy soil,
respectively, are 0.022m, 0.013m, 0.253m, and 4.446m. Because water and oil
generally
coexist in the formation, the efficient heating of formation water and the
heat conduction
between local water and oil partially compensate for the relative inefficiency
of
dielectric heating of matrices and oil. Also, crude oils often contain
conductive
impurities which may increase the loss, and thus generate substantial heat. In
rock
formation where matrix volume is greater than pore volume, it is reasonable to
expect an
effective penetration depth of 7-10cm. This depth is sufficient for borehole
NMR
measurements. Based on further experimentation on actual temperature
dependence of
properties of heavy oil, the expected depth of penetration may be different.
[0023] The requirements for heating power depends on the specific heats of the
materials
that constitute the fluid-bearing rock formation. As an example, the values of
specific
heat for water, crude oil, clay, limestone at room temperature are 4.2, 2.2,
1.0, and 0.92
kJ/kg/ C, respectively. For a 20 % porosity rock, in which 80% of rock volume
is matrix
volume, the overall specific heat of formation is thus about 1.4 kJ/kg/K.
Assuming an
8" borehole and a 1 kW directional, idealized microwave device such as an open
waveguide with an aperture of 36 and further assuming the formation response
to this
microwave source has a penetration depth of DP = 2 to 4 inches, the rise in
temperature
over this volume ranges from 57 to 25 T /min. These values assume a density of
formation pf = 2.34kg/liter. Overall, power dissipation into the dielectric
media is 64%
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of the incident power. Although power loss due to non-ideal microwave sources
and
conductive media need to be included for real situations, the heating time
required for a
small sensor is of the order of few minutes. This is acceptable for NMR
logging or
stationary measurements. Due to exponential temperature decay at distances
away from
the borehole wall, it is desirable to use multiple frequency NMR sensors which
measure
signals at different depths of investigation. For large apertured NMR sensors,
usually a
stationary measurement of a large heated area is more practical.
[0024] Fig. la shows the effect that changing the time interval between CPMG
pulses,
TE, has on the appearance time of the T2 peak of crude oil at a temperature of
30 C. The
peak for a pulse sequence with TE = 0.5 ms (101) appears at 0.5 ms. At the
same
temperature, increasing the duration of the pulse sequence to TE = 2.4 ms
causes the T2
peak to appear at 2 ms (103). It is important to note that the 2ms peak of
TE=2.4 ms is
incorrect because little can be detected for porosity components having
T2<2ms. This
situation results in an underestimation of porosity and viscous oil
saturation.
[0025] In Fig. lb, the same pulse sequences are represented with the
temperature now is
raised to 75 C. At this temperature, the T2 peak from a CPMG measurement with
TE=0.5 ms now appears at approximately 2 ms (104). Furthermore, the peak of
the
response to the TE = 2.4 ms sequence also occurs at approximately 2 ms (106).
There is
no discernable diminution of the peak at TE = 2.4 ms, allowing the
practitioner a more
accurate reading of the porosity. Figs. la and lb show that changing the
temperature of
the environment can have a noticeable effect on the peak response readings.
[0026] The intrinsic relaxation time T2 of oil, changes significantly
depending on the
temperature of the oil. Specifically, as temperature increases, the T2 peak of
heavy oil
appears at later times. Figs. 2a and 2b display the effect of heating on the
T2
distributions. This shift in the T2 spectrum is expected to occur only for
oil, due to the
fact that for a water-wet system, the surface reflexivity is independent of
temperature,
CA 02461995 2004-03-29
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meaning that a smaller shift is expected for the T2 of water. Due to the
diffusivity of
water increasing with temperature, the diffusion effect tends to slightly
shift the apparent
T2 to earlier times. Therefore increasing temperatures will shift the heavy
oil to longer T2
times and will shift the water to shorter T2 time, facilitating the
differentiation of oil and
water NMR signals. The shift of water T2 usually is insignificant for the
faster decaying
BVI and CBW water signal is dominated by surface relaxation. Furthermore, by
comparing spectra acquired at different temperatures, the practitioner can
identify and
quantify oil and water saturation.
[0027] Fig. 2a shows the effects of temperature on the timing of the response
peaks, with
TE held constant at TE = 0.5 ms. The curves represent readings taken at
temperatures of
30 C, 45 C, 60 C, and 75 C. The peak for T = 30 C (201) occurs at
approximately 2 ms.
As temperature increases, the peak migrates to later times, such that the peak
for T =
75 C (202),occurs at approximately 10 ms.
[0028] Fig. 2b shows the same experiment with the CPMG pulse interval
maintained at
TE = 1.2 ms. As in Figure 2a, temperature is changed from 30 C, 45 C, 60 C,
and
finally 75 C. As in Figure 2b, the peak migrates to later times as temperature
increases.
At 30 C, the peak occurs at 2 ms (203), and at 75 C, the peak occurs at 10 ms
(204). The
examples shown in Figures 2a and 2b indicate that 40 -50 C temperature rise
does make
important differences for detecting heavy oils. Change from 2ms to l Oms
clearly
separates oil from CBW as the latter usually relaxes with T2<_3ms.
[0029] The embodiment of the invention is designed to be operated in both
single
frequency mode or multiple frequency mode in order to obtain different types
of
information. In a single frequency mode, the practitioner can take NMR
measurements
indicative of porosity and saturation of heavy oils and interleave
measurements with the
microwave heating process to obtain temporal profiles of the NMR properties.
Using a
multiple frequency tool, the practitioner can obtain profiles of the T2
spectrum and other
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NMR properties as a function of depth of sensitive volume (i.e., depth of
investigation,
DOI). Since the heating efficiency is depth dependent, the temperature is DOI
dependent, and, thus, the depth profiles of the NMR response correspond to the
temperature profile of the NMR response. On the other hand, another method for
determining near-wellbore formation temperature is to use the existing arts of
simulation
techniques. For example, Fanchi in SPE Paper 20483 shows examples of
temperature
distribution in reservoirs heated by electromagnetic irradiation.
[0030] Principally any state-of-art NMR logging tools can be used in
conjunction with
the microwave heating device described in this invention. However, to heat a
large
volume in the formation usually requires longer times which may not be
practical to
logging applications. Therefore, a small apertured, preferably pad or side
looking, NMR
sensor focused in a small locality of formation is more desirable. Such a side-
looking
NMR assembly is disclosed in US Patent 6348792 to Reiderman et al and having
the
same assignee as the present application. A small sensor also reduces the
power
consumption thus leaving more power for microwave heating. A heated formation
volume usually takes quite long time to cool down, therefore, for continuous
logging
while heating, a long-slit type of microwave antenna is placed in the front of
the NMR
device to provide pre-measurement heating of the formation.
[0031] The borehole fluid usually acts as a conductive media where microwave
can be
attenuated quickly. Thus, the microwave heating device is desired to have a
good contact,
or at least in a very close proximity, of the borehole wall.
[0032] In one embodiment of the invention, the microwave device used for
heating is
also used for determining dielectric properties of the earth formation, as the
microwave
frequency band is suitable for dielectric measurements. Oil saturation can
potentially be
determined by utilizing their differences between the loss tangents of oil
(>1000e4) and
water (<100e4). A noticeable difference appears in the imaginary component of
the
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CA 02461995 2009-11-09
dielectric constants of each (80 for oil and 2 for water). The tan b for water
decrease as
temperature increases. There is not enough current information on the
temperature
depend of tan S for many types of oils. However, tan S for water is also
dependent on
frequency. Measuring formation at two frequencies provides additional means to
determine oil/water saturations.
[00331 Another embodiment of the invention uses the reservoir fluid
characterization
RCITM tool of Baker Hughes Inc. at an increased temperature. Details of the
operation of
the tool are given, for example, in US Patent 5,377, 755 and US Patent 5,303,
775 to
Michaels et al, having the same assignee as the present invention. Although
the
embodiment is not for use in close contact with the rock formation, due to
significant
microwave attenuation in water, the source of the microwaves must be placed in
contact
with the formation. In the RCITM operation, reservoir fluids are extracted
from formation
using a pressure pump. Because of the low mobility of viscous oil, it requires
very high
pressure to extract viscous oils from formation, often in the risk of causing
formation
damage. When the local formation temperature is raised, the oil viscosity
decreases.
Thus, the reservoir fluids can be extracted under a reduced pumping pressure
thereby
reducing the risk of formation damage.
[00341 The data obtained at elevated temperature can be used in two ways.
Firstly, for
petrophysical quantities that are temperature independent, such as saturation
and
porosity, the estimated values obtained at the increased temperature should be
the same
as that in original reservoir temperature condition. For fluid properties that
are
temperature dependent, such as viscosity, the values obtained at the increased
temperature are extrapolated back to its equilibrium reservoir temperature.
Secondly,
production of many heavy oil reservoirs requires the application of an
enhanced oil
recovery method because there is little spontaneous flow. The use of heating
is one of the
commonly used enhanced oil recovery methods. Oil properties measured at the
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increased temperature provide the exact information useful to predict the
production
potential if the enhanced oil recovery method is necessary.
[0035] Any of the described methods above (active or passive heating,
refrigeration etc.)
thus reversibly alters a property (temperature) of the formation. The
alteration in
temperature changes a parameter of interest that is measured by a sensing
device within
the formation. In broad terms, the present invention takes advantage of the
difference in
the parameter of interest.
[0036] Fig. 3 shows an exemplary tool suitable for use with the method of the
present
invention. Shown is a borehole 310 which has been drilled in a typical fashion
into a
subsurface geological formation 312 to be investigated for potential
hydrocarbon
producing reservoirs. A logging tool 314 has been lowered into the hole 310 by
means of
a cable 316 and appropriate surface equipment represented diagrammatically by
a reel
318 and is being raised through the formation 312 comprising a plurality of
layers 312a
through 312g of differing composition, to log one or more of the formation's
characteristics. The logging tool is provided with bowsprings 322 to maintain
the tool in
an eccentric position within the borehole with one side of the tool in
proximity to the
borehole wall. The logging tool 323 includes an NMR sensor 325 and a microwave
heating device 327. In the example shown, the microwave heating device is
shown
below the NMR sensor. Alternatively, the microwave heating device may be
placed
above the NMR sensor. The latter arrangement is usually preferable wireline
tools in
which measurements are typically made with the wireline being pulled up from
greater
depths. The former arrangement (i.e., microwave heating device below the NMR
sensor).
is usually preferable in MWD applications.
[0037] As an alternative to or in addition to the NMR sensing device,
dielectric
measurements of the earth formation and/or fluids may be made by a suitable
microwave
sensing device (not shown). Exemplary tools and methods for determination of
dielectric
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CA 02461995 2009-11-09
properties of earth formations are described in U. S. Patents 4,052, 662 and
4,893, 084 to
Rau. It should be noted that other microwave devices for determination of
formation
dielectric constant may also be used. It should also be noted that when a
microwave
sensing device is used, a heating device may not be necessary,i e., the
heating device and
the sensing device may be the same.
100381 Signals generated by the tool 314 are passed to the surface through the
cable 316
and from the cable 316 through another line 319 to appropriate surface
equipment 320
for processing, recording and/or display or for transmission to another site
for processing,
recording and/or display. It should also be noted that in Fig. 3, the NMR
sensor and the
microwave heating device are shown on a single tool. It is also possible to
have them on
different assemblies that can be strung together.
[00391 The present invention has been described with reference to a wireline
device.
However, the principles of the invention may also be embodied in and used with
MWD
devices conveyed on a drilling tubular such as a drilling or coiled tubing.
[00401 While the foregoing disclosure is directed to the preferred embodiments
of the
invention, various modifications will be apparent to those skilled in the art.
It is intended
that all variations within the scope and spirit of the appended claims be
embraced by the
foregoing disclosure.
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