Centrifuge bucket and method of use

A bucket for use in a swinging bucket centrifuge. A core holder is located between two end chambers, with the annular space between the core holder and the bucket sidewall maintaining the chambers in fluid communication. Windows at each end of the bucket allow fluid collections to be monitored. This enables more accurate data to be obtained regarding the effect of fluids of different specific gravity on a fluid saturating a sample. For example, to obtain data allowing a more accurate modeling of reservoir conditions in an oil field impacted by both gas and water displacement, the amount of oil expelled from a rock sample by gas under pressure and temperature conditions simulating those in the reservoir is measured and, after replacing the gas with water, the amount of oil expelled by water under simulated conditions is measured.

FIELD OF THE INVENTION 
This invention relates to a bucket-type centrifuge adapted for use in 
studies of core samples of oil-bearing rock formations. More particularly, 
it relates to a new design of centrifuge bucket which enables data to be 
obtained in a single experiment for the purpose of studying the effects of 
both gas and water drainage on an oil-bearing rock formation under 
reservoir ambient conditions. 
BACKGROUND OF THE INVENTION 
In order to determine the distribution or effect of fluids in oil-bearing 
rock formations from test samples it is common to saturate a core sample 
of the rock with one of the fluids and to submerge the sample in another 
fluid in a centrifuge chamber. Typically, one of the fluids is oil from 
the rock formation and the other is water or gas. Because the fluids are 
immiscible and of different densities, when the centrifuge is rotated some 
of the fluid in the sample is expelled and replaced by the other fluid. 
This can be noted and measured through a window provided in the bucket. 
When dealing with an oil-bearing formation that is impacted by both gas and 
water displacement, such as studies involving the effects of water 
injection in a gas gravity drainage field, it has been necessary to use 
two different centrifuge buckets in two separate experiments conducted at 
ambient conditions. Typically, an oil-saturated core sample is placed in a 
centrifuge bucket and gas is injected into the centrifuge chamber. When 
the centrifuge is rotated gas will expel some of the oil in the sample. 
Because the oil has a greater specific gravity than the gas, it collects 
in the window area at the outer extremity of the bucket. Then the 
oil-saturated sample, which now contains only the oil which was not 
expelled during the above experiment, is submerged in a water-filled 
centrifuge bucket of different design wherein the window area is at the 
inner extremity of the bucket. Upon rotation of the centrifuge oil is 
expelled from the sample and, having a lower specific gravity than water, 
collects in the window area at the inner extremity of the bucket. The 
results of both experiments then have to be integrated in order to 
determine the calculated effect of the gas and water in the formation. 
This is not an entirely reliable procedure, however, because the 
experiments are not conducted under reservoir conditions, and the actual 
conditions in the reservoir are often not adequately reflected in a model 
based on the data collected. This problem is made worse by the fact that 
the sample loses its gas saturation from the first experiment, thereby not 
enabling actual reservoir conditions to be reflected during the second 
experiment. 
Another approach to the study of a three phase gas/water/oil system is to 
use coreflooding experiments. Such procedures require the use of large 
cores, in the order of four to five feet long, which have to be flooded at 
an extremely slow rate, often requiring months to complete the operation.. 
Moreover, capillary pressure causes oil to be held in the ends of the 
core. Since such oil would not normally be present in a reservoir, this 
tends to give misleading results. Coreflooding experiments are therefore 
not practical as a means of quickly obtaining an accurate model of such a 
reservoir. Coreflooding experiments are, in addition, quite expensive to 
carry out. 
It would be desirable to be able to obtain data which more realistically 
reflects actual conditions in a reservoir affected by both gas and water 
pressure, and to do so rapidly, accurately and economically. Further, it 
would be desirable to be able to collect such data in a single experiment 
rather than in two separate experiments. 
BRIEF SUMMARY OF THE INVENTION 
The centrifuge bucket of the invention is not limited to use in any 
particular type of centrifuge. For example, it may be designed to be used 
in a conventional swinging bucket type of centrifuge, wherein the bucket 
is pivotally mounted on a centrifuge support, or in a centrifuge wherein 
the buckets are horizontally mounted, as by screw threads, in a central 
rotating support. In either case the buckets are substantially 
perpendicular to the rotary shaft of the centrifuge during rotation. Each 
bucket has two liquid collection chambers, the first being adjacent the 
inner end of the bucket, or in other words the end closer to the rotary 
shaft during rotation of the centrifuge, and the second being adjacent the 
opposite outer end of the bucket. A sleeve or other means for receiving 
and supporting a sample core is located between the first and second 
collection chambers so that the sample core is in fluid communication with 
the collection chambers. In addition, a liquid passageway connects the 
first and second collection chambers. 
With this arrangement liquid expelled from a sample core in a centrifuge 
operation by a fluid of greater specific gravity than that of the expelled 
liquid will collect in the first chamber, and liquid expelled from the 
sample core by a fluid of lesser specific gravity than that of the 
expelled liquid will collect in the second chamber. A window adjacent each 
end of the bucket permits collected liquid in each chamber to be 
monitored. 
Preferably, the liquid passageway connecting the first and second 
collection chambers comprises an annular space between the sample core 
sleeve and the sidewall connecting the chambers, and the inner end of each 
bucket comprises a closure cap including means for receiving at least one 
fluid line so as to be in fluid communication with the first collection 
chamber. 
The bucket lends itself to the laboratory study of oil reservoirs which are 
affected by both gas and water, such as, for example, studies determining 
the effect of water injection in a gas gravity drainage field on oil 
recovery rate, or the effect of gas injection in a water gravity drainage 
field. Obviously, however, it would also be useful in determining the 
effect of any fluids of lesser or greater specific gravity than that of 
the fluid saturating the core sample. Data may be obtained for this 
purpose by inserting the saturated core sample into the core sleeve of the 
bucket, introducing a first fluid of low specific gravity into the bucket 
through a first valve, closing the valve and rotating the centrifuge to 
expel a portion of the core-saturating fluid from the sample into the 
second collection chamber referred to above. When gas is utilized as the 
first fluid and oil is the core saturant, this action simulates gravity 
drainage in an oil reservoir under the influence of a gas cap drive. The 
centrifuge is then stopped and a second fluid of high specific gravity is 
introduced into the bucket through the first valve while allowing the 
first fluid to escape from the bucket through a second valve which is 
connected to a back pressure regulator. Oil expelled from the core sample 
along with the first fluid will flow to the top of the second fluid and 
can be accounted for in this manner. The valves are then closed and the 
centrifuge is again rotated to expel an additional amount of the 
core-saturating fluid from the sample into the first collection chamber 
referred to above. The data thus produced can be used to more accurately 
model reservoir gravity drainage. 
If desired, the first fluid can be a higher density fluid the core saturant 
and the second fluid may be less dense. Thus, water gravity drainage in an 
oil reservoir may be simulated by utilizing water as the first fluid and 
gas as the second fluid. In such a case, when introducing gas into the 
bucket while allowing water to escape, any oil produced during this 
process may be collected and measured. 
In either case, the back pressure regulator maintains the same pressure in 
the bucket when switching from one drive fluid to the other. Thus, to more 
accurately simulate conditions of the reservoir, gas introduced into the 
bucket as the low specific gravity fluid is maintained at reservoir 
pressure and temperature during centrifuging. Similarly, water introduced 
as the high specific gravity fluid is also maintained at reservoir 
pressure during centrifuging. 
These and other features and aspects of the invention, as well as other 
benefits, will readily be ascertained from the detailed description of the 
preferred embodiment described below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1 and 2, a swinging bucket centrifuge 10 is illustrated 
which is comprised of a central bucket support 12 attached to a center 
shaft 14, the support including outwardly extending attachment flanges or 
brackets 16. While the support 12 is illustrated as having four pairs of 
mounting brackets for receiving four buckets, the centrifuge may be 
designed to support a lesser or greater number of buckets. A bucket 18 is 
attached to each pair of brackets by pivot or trunnion pins 20 which 
extend inwardly from opposite brackets and are received in suitable 
openings 21 in the bucket. As shown in FIG. 2, each bucket is of elongated 
shape compared to conventional buckets, with a viewing window 22 located 
in the upper portion of the bucket and another viewing window 24 located 
in the lower portion of the bucket. Each bucket additionally incorporates 
valves 26 and 28 at the upper end of the bucket which communicate with the 
bucket interior in a manner described in more detail below. 
The shaft 14 is adapted to be rotated by a motor, not shown. Any suitable 
motor capable of providing the high rotational speeds required in a 
centrifuging operation may be employed. Speeds in the range of 200 to 
20,000 RPM, for example, are normally required in order to expel fluid 
from a saturated sample at the rates required to generate sufficient data. 
It will be understood that the buckets in FIGS. 1 and 2 are shown in the 
horizontal position they assume when the centrifuge is rotating. When the 
centrifuge is at rest, the buckets hang from their support flanges in the 
vertical position indicated by dotted lines in FIG. 1. The bottom of the 
bucket when at rest thus becomes the outer end when spinning and the top 
of the bucket at rest becomes the inner end when spinning. Since the 
invention may be incorporated in buckets which are adapted to be supported 
by means other than by a swinging bucket mounting, it will be understood 
that the swinging bucket arrangement described is for illustrative 
purposes only. Buckets incorporating the features of the invention could, 
for example, be attached directly to the central support, as by screw 
threads, so that they are maintained in a horizontal position both when 
spinning and when at rest. 
Referring now to FIGS. 3 and 4, the bucket 18 includes an outer casing 30 
comprised of a relatively large diameter upper flange portion 32 and a 
relatively small diameter lower tubular portion 34. The lower end of the 
tubular portion 34 is closed by an integral end wall 36, and a cup-shaped 
insert 38 inside the bucket is supported by the end wall 36. Supported on 
the insert 38 is a tube or cylinder 42 which in turn supports tubular core 
receptacle or sleeve 44, as by radially spaced ribs or welds 46 or any 
other convenient means of supporting the core holder coaxially with the 
cylinder 42 so as to create an annular space 48 therebetween. The core 
sleeve 44 is open at its upper end and contains an opening or conduit 50 
at the midpoint of lower end wall 52 through which liquid expelled from a 
sample can flow. The end wall 52 is thicker adjacent the conduit 50 than 
at the ends, so that the end wall slopes away from its midpoint, thereby 
facilitating the flow of liquid from the end of the bucket toward the 
annular space 48. 
The upper end of the flange portion 32 is counterbored as at 54 in order to 
receive and support cap 56. The bottom of the cap 56 also engages the 
upper edge of ring or cylinder 58, and the bottom of the cylinder 58 
engages the top of cylinder 42. The upper and lower ends of the cylinder 
42 are counterbored so as to fit into counterbores in the lower edge of 
the cylinder 58 and the upper edge of the insert 38. This arrangement 
provides for a smooth flow path in the annulus between the core holder 44 
and the cylinder 42. O-rings 60 and 62 in the counterbored portions of the 
insert 38 and the cylinder 58, respectively, prevent leakage at the upper 
and lower ends of the cylinder 42, and an O-ring 64 in the upper edge of 
the cylinder 58 prevents leakage between the cylinder 58 and the cap 56. 
The cap 56 also contains threaded bores or sockets 66 and 68 extending from 
the upper surface of the cap, and conduits 70 and 72 which connect the 
sockets 66 and 68, respectively, to the lower surface of the cap. 
Positioned in the sockets 66 and 68 are valve bodies 74 and 76, 
respectively, which incorporate the valves 26 and 28 referred to earlier. 
Any suitable valve design capable of withstanding the high pressures 
involved and small enough to be utilized with the centrifuge bucket of the 
invention may be utilized. One suitable valve design is shown in FIG. 6, 
wherein the valve 74 is a needle valve having a valve stem 82 terminating 
at its lower end in the needle nose 84 and terminating at its upper end in 
a slot 86 capable of receiving a screwdriver blade. The needle 84 seats in 
the upper end of a conduit 88 in the valve nut 90. The valve nut 90 is 
threaded into threaded bore 92 in the bucket cap 56, which connects with 
the conduit 70 in the cap. A conduit 94 extending through the valve body 
96 connects with the conduit 98 in the valve nut through which the valve 
stem 82 moves. The upper portion of the conduit 98 is enlarged and 
threaded, as at 100, to cooperate with the threads 102 on the upper 
portion of the valve stem 82. O-rings 104 and 106 are positioned on the 
valve stem and in a groove in the valve nut, respectively, to prevent 
leakage. In operation, it is merely necessary to back off the valve stem 
by turning it with a screwdriver in order to open the conduit 88 to the 
conduit 94, through which driving fluid is moved. To ready the bucket for 
a centrifuge operation, the valve is closed by turning the valve stem in 
the opposite direction, disconnecting the source of fluid from the conduit 
94 and closing the conduit 94 with a sleeve or other plug. 
To assemble the centrifuge bucket components it is merely necessary to 
slide the insert 38 to the bottom of the bucket, seat the cylinder 42 in 
place, thereby properly positioning the attached core holder 44 at the 
same time, and slide the upper ring or cylinder 58 into place until it 
seats against the counterbored upper end of the cylinder 42. The cap 56 is 
then pushed into place to form the arrangement shown in FIG. 3. It will be 
understood that the O-rings 60, 62 and 64 will have been installed in 
their grooves prior to assembly. The dimensions of the insert 38, the 
cylinder 58 and the cap 56 are such that they simply slide into place in 
the bucket shell. Their close tolerances and the centrifugal force of the 
rotating centrifuge maintain the components in their initial relationship 
throughout the centrifuge operation. The cap is readily moved into and out 
of its seat by maintaining the valves in the plugs 74 and 76 open, thereby 
allowing the pressure within the bucket to be equalized with the outside 
pressure by means of the open path through the conduits 70 and 72 and the 
plugs 74 and 76. Although the cylinder 42 is shown as being spaced from 
the outer shell 30, the wall thickness of the cylinder may be made 
greater, if desired, causing the cylinder to be closer to the outer shell. 
Since the cylinder 42 is not exposed to any increased pressure during 
operation, the wall thickness need only be sufficient to adequately 
support the sample core sleeve 44, so that any such extra thickness is not 
needed and preferably is not provided. 
The structure described provides for an outer chamber 78 between the bottom 
end wall 52 of the core sleeve 44 and the bottom wall 36 of the bucket 
shell 30. An inner chamber 80 is also provided between the top of the core 
sleeve 44 and the cap 56, with the two chambers being connected by the 
annular space 48. The window 22 is located in the flange portion 32 to 
permit the level of liquid in the chamber 80 to be monitored, while the 
window 24 is located in the bottom or outer end portion of the shell 30 to 
permit the level of liquid in the chamber 78 to be monitored. This of 
course requires the cap 58 and the cup 38 to be formed of suitable 
transparent material so that the level of liquid in the spaces 78 and 80 
can be seen through the windows. 
Referring now to FIGS. 5A-5C, which are simplified illustrations of the 
bucket of the invention, showing the relationships of the core sleeve 44 
and the essential components of the bucket, a method of using the bucket 
to determine the effect of water injection in a gas gravity drainage field 
will be described. A core sample S is placed in the holder and the bucket 
is assembled as previously described. The core sample will have been 
saturated with oil from the reservoir in question at connate water 
saturation. Gas of the type under investigation is supplied from a 
pressurized gas source 82 through the fluid line 84 to the open valve 26, 
with the valve 28 open to the back pressure regulator 86 which is 
maintained in closed condition, until the pressure in the bucket reaches 
the pressure of the reservoir under study. The gas is equilibrated with 
the oil at reservoir temperature. The valves 26 and 28 are then closed and 
the line 84 and back pressure regulator 86 are removed from the valve 
plugs 74 and 76 as shown in FIG. 5B. The centrifuge is then rotated and 
oil in the sample is expelled by the gas and collected in the chamber 78 
as a result of the oil being of greater specific gravity than the driving 
fluid. The operation is continued until the amount remaining in the sample 
corresponds to the saturation level in the reservoir due to gas gravity 
drainage. The amount collected can be monitored through the window 24. 
The centrifuge is then stopped, and a back pressure regulator 86 set at the 
reservoir pressure is connected to the valve 28. Both valves 26 and 28 are 
opened and water from a source 88 is then supplied through fluid line 90. 
This arrangement is illustrated in FIG. 5C. Water enters the bucket, 
eliminating the gas, and exits through the valve 28. With the pressure of 
the water being maintained at the desired level by the pressure regulator, 
both valves 26 and 28 are closed and the conduit 90 and pressure regulator 
86 removed. The bucket at this time is again a closed system as it appears 
in FIG. 5B. At this point, oil may float up through annular space 48 from 
the chamber 78 to the chamber 80. The centrifuge is again rotated until 
the point of residual oil saturation is reached, with the oil being 
recovered in chamber 80 as a result of the oil being of lesser specific 
gravity than the driving fluid. The collection in this case is monitored 
through window 22. The data thus collected can be used to provide a more 
realistic model of the reservoir than is possible by collecting data 
through the old method of running two separate experiments with separate 
buckets for the gas phase and the water phase. 
The bucket also lends itself to be used to determine the effect on oil 
recovery of gas injection in a water-invaded oil field. Data is obtained 
for this purpose by inserting the oil-saturated core sample into the core 
sleeve of the bucket, introducing a first fluid of high specific gravity, 
such as water, into the bucket through the valve 26 as shown in FIG. 5C, 
closing the valve and rotating the centrifuge to expel a portion of the 
oil from the sample into the collection chamber 80. The centrifuge is then 
stopped and turned upside down to the position shown in FIG. 5D. A second 
fluid of low specific gravity, such as gas, is introduced into the 
inverted bucket through the valve 26 while allowing the first fluid to 
drain down from the bucket through the valve 28. The centrifuge is then 
again turned to upright position. The valves 26 and 28 are then closed and 
the centrifuge is again rotated to expel an additional amount of fluid 
from the sample into the collection chamber 78. The data thus collected 
can be used to more accurately model reservoir gas/oil and water/oil 
drainage. 
Although the bucket has special utility in enabling the experiment outlined 
above to be run, it will be appreciated that its usefulness is not limited 
to this particular experiment but may be employed to determine 
relationships in any three-phase fluid system where the driving fluids are 
of lesser and greater specific gravity, respectively, than that of the 
saturating fluid. It is also possible within these parameters to test more 
than one fluid of the same order of density in the bucket of the 
invention. For example, a first gas can be used as a driving fluid, 
followed by a second gas, followed by a liquid of higher specific gravity. 
Another possible test procedure is to first introduce a high density 
driving fluid such as water, followed by another high density liquid, such 
as water which has been altered in some manner from the first driving 
fluid, as for example by including a different amount of a modifier such 
as a different surfactant solution. 
Another embodiment of the bucket of the present invention is illustrated 
generally as 118 in FIG. 7 and includes an outer casing 130 which is 
comprised of a first flange portion 132, a second flange portion 133, and 
a tubular portion 134. First flange portion 132 is provided with openings 
121 to attach the bucket to a bracket by means of pivot or trunnion pins 
20. The outer end of first flange portion 132 is counterbored as at 154 in 
order to receive and support cap 156. Cap 156 also engages an end surface 
of first ring or cylinder 158, while the other end surface of cylinder 158 
engages the top of a generally tubular core receptacle or sleeve 144. A 
first chamber 180 is defined within the interior of first ring or cylinder 
158 and is bounded at one end by cap 156 and at the other end by sleeve 
144 and the core sample which is inserted therein. Core sleeve 144 has an 
end wall 152 which is constructed with an opening or conduit 150 proximate 
the center thereof through which liquid expelled form a sample can flow. 
End wall 152 is thicker adjacent conduit 150 than at the perimeter thereof 
so as to define a slope which facilitates the flow of liquid initially 
passing through conduit 150 away form such conduit. Core receptacle or 
sleeve 144 also engages an end surface of second ring or cylinder 188. The 
outer end of second flange portion 133 is counterbored as at 184 in order 
to receive and support second cap 190. Cap 190 also engages an end surface 
of second ring or cylinder 188. A second chamber 181 is defined within the 
interior of second ring or cylinder 188 and is bounded at one end by cap 
190 and at the other end by end wall 152 of core sleeve 144. O-rings 162 
and 164 are positioned so as to prevent leakage between core receptacle or 
sleeve 144 and first and second rings or cylinders 158, 188 and between 
first and second rings or cylinders 158, 188 and caps 156, 190. 
Cap 156 contains threaded bores or sockets 166, 168 extending from the 
upper surface of the cap, and conduits 170, 172 which connect sockets 166, 
168, respectively, to the lower surface of the cap. Positioned in the 
sockets 166, 168 are valve bodies 174, 176, respectively, which 
incorporate the valves 26, 28, referred to earlier. In a similar manner, 
cap 190 also contains threaded bores or sockets 191, 192 extending from 
the upper surface of the cap, and conduits 198, 199 which connect sockets 
191, 192, respectively, to the lower surface of the cap. Positioned in the 
sockets 191, 192 are valve bodies 194, 196, respectively, which 
incorporate valves 26, 28 as described above. Assembly of this embodiment 
of the bucket of the present invention will be readily apparent to a 
skilled artisan in view of the assembly previously described with respect 
to embodiment illustrated in FIG. 3. 
Each bucket 118 is provided with viewing windows 22 and 24. Window 22 is 
located in the upper portion of the bucket as illustrated in FIG. 2 to 
permit visual observation of first chamber 180. Window 24 is located in 
the lower portion of the bucket, e.g. in second flange portion 133, to 
permit visual observation of the second chamber 181. 
A method of using the embodiment of the bucket illustrated as 118 to 
determine the effect of water injection in a gas gravity drainage field 
will be described. A core sample which has been saturated with oil from 
the reservoir in question at connate water saturation is placed inside 
sleeve 144 which in turn is loaded into the outer casing 130. O-rings 162 
and 164 are mounted in cylinder 158, and the cylinder is placed inside the 
outer casing 130 to engage the end surface of sleeve 144. Cap 156 is 
secured in place, engaging the end surface of cylinder 158. The first 
chamber 180 is and the second chamber are simultaneously filled with gas 
of the type under investigation from a common pressurized gas source. 
Chamber 180 is supplied with gas via an open valve 26 within valve body 
174 and conduit 170, while chamber 181 is supplied with gas via an open 
valve 26 within valve body 194 and conduit 198. Valves 28 within valve 
bodies 176 and 196 are open to a common pressure regulator 86 (not 
illustrated in FIG. 7) which is maintained in a closed position until the 
pressure in bucket 118 reaches the pressure of the reservoir under study. 
The gas is equilibrated with the oil at reservoir temperature. All valves 
26 and 28 are then closed and the back pressure regulator and all lines 
connecting valves 28 thereto and any lines connecting valves 26 with the 
pressurized gas source are removed from the bucket. The centrifuge is then 
rotated and oil in the sample is expelled by the gas and collected in the 
second chamber 181 as a result of oil being of greater specific gravity 
than the driving fluid. The operation is continued until the amount of oil 
remaining in the sample corresponds to the saturation level in the 
reservoir due to gas gravity drainage. The amount of oil collected can be 
monitored through the window 24. 
The centrifuge is then stopped and a back pressure regulator 86 (not 
illustrated in FIG. 7) which is set at the reservoir pressure is connected 
to the valves 28 within valve bodies 176 and 196. Both valves 26 within 
valve bodies 174 and 194 and valves 28 within valve bodies 176 and 196 are 
opened and water from a source 88 (not illustrated in FIG. 7) is supplied 
through valves 26 and conduits 170 and 198 into chamber 180 and 181, 
respectively, thereby eliminating the gas from chamber 180 which exits 
through conduit 172 and valve 28 and gas and oil from chamber 181 which 
exits through conduit 199 and valve 28. It is preferred to invert the 
bucket at least once during this procedure to ensure that substantially 
all the oil and gas present in chamber 181 is displaced by water. With the 
pressure of the water being maintained at the desired level by the 
pressure regulator, both valves 26 and 28 are closed and the back pressure 
regulator and any lines connecting valves 26 with the water source are 
removed from the bucket. The centrifuge is again rotated until the point 
of residual oil saturation is reached, with the oil being recovered in 
chamber 180 as a result of the oil being of lesser specific gravity than 
the driving fluid. The collection in this case is monitored through window 
22. As previously mentioned, the data thus collected can be used to 
provide a more realistic model of the reservoir than is possible by 
collecting data via the old method of running two separate experiments 
with separate buckets for the gas phase and the water phase. 
Bucket 118 of this embodiment also lends itself to be used to determine the 
effect on oil recovery of gas injection in a water-invaded oil field. A 
core sample which has been saturated with oil form the reservoir in 
question is placed inside sleeve 144 which in turn is loaded into the 
outer casing 130. O-rings 162 and 164 are mounted in cylinder 158, and the 
cylinder is placed inside the outer casing 130 to engage the end surface 
of sleeve 144. Cap 156 is secured in place, engaging the end surface of 
cylinder 158. Valves 28 within valve bodies 176 and 196 are open to a 
common pressure regulator 86 (not illustrated in FIG. 7). Both valves 26 
within valve bodies 174 and 194 are opened and water from a common source 
88 (not illustrated in FIG. 7) is supplied through valves 26 and conduits 
170 and 198 to simultaneously fill chambers 180 and 181, respectively, 
while air escapes through conduits 172 and 199 and valves 28. As 
previously described, it is preferred to invert the bucket at least once 
during this procedure to ensure that substantially all the air present in 
chamber 181 is displaced by water. All valves 26 and 28 are then closed 
and the back pressure regulator and any lines connecting valves 26 with 
the water source are removed form the bucket. Bucket 118 is then loaded 
into the centrifuge and spun. While the bucket is spinning, water from the 
first chamber 180 displaces some of the oil in the core, and the oil 
enters chamber 180. The contact between the oil and the water in chamber 
180 can be viewed through the chamber window 22. After spinning, the 
bucket 118 is removed from the centrifuge. Valves 26 in valve bodies 174 
and 194 are connected to a gas line and valves 28 in valve bodies 176 and 
196 are connected to a water receptacle. The valves 26 and 28 are opened, 
and gas enters chamber 181 via valve 26 and conduit 198 while water and 
oil exit chamber 180 via conduit 172 and water exits chamber 181 via 
conduit 199. It is again preferred to invert the bucket at least once 
during this procedure to ensure that substantially all the water and oil 
present in chamber 180 is displaced by gas. Valves 26 and 28 are then 
closed and disconnected form the gas line and the water receptacle. The 
bucket is reloaded into the centrifuge and spun again. While the bucket is 
spinning, the gas in chamber 181 displaces water and oil in the core, and 
the water and oil enter chamber 181. The fluid levels in chamber 181 can 
be viewed through window 24 while the bucket 118 is spinning. The 
centrifuge is then stopped and the bucket 118 is removed. The data thus 
collected can be used to more accurately model reservoir gas/oil and 
water/oil drainage. 
It will now be apparent that the ability of the invention to permit use of 
a single bucket instead of switching buckets to gather data for studies of 
core samples allows the same gas saturation in the sample under continuing 
pressure prior to displacement with a higher density fluid. This will be 
understood by those skilled in the art to improve the accuracy of the data 
due to the ability to maintain simulated reservoir conditions. Further, as 
indicated previously, the invention results in a distinct advantage over 
the use of coreflooding experiments by minimizing the capillary end effect 
which exists in the coreflooding sample but not in the reservoir. 
Tests can be conducted through a wide range of temperatures by heating the 
centrifuge. Temperatures up to 250.degree., for example, can readily be 
achieved, enabling reservoir conditions to be simulated. The invention 
also contemplates the use of light to heavy oil as the saturant, as 
reservoir conditions dictate. 
Although a specific bucket design has been disclosed which is simple to 
load and assemble and which is highly functional, it will be understood 
that other designs which provide for the core sample sleeve to be located 
so as to provide a clear flow path connecting the inner and outer 
collection chambers can be employed. Further, it should be understood that 
changes to other features and aspects which do not affect the overall 
basic function and concept of the invention may be made by those skilled 
in the art without departing from the spirit and scope of the invention, 
as defined by the appended claims.