Method employing pressure transients in hydrocarbon recovery operations

Abstract

A method to induce pressure transients in fluids for use in hydrocarbon recovery operations by inducing the pressure transients in a fluid by a collision process. The collision process employs a moving object (103,203,303,403) that collides outside the fluid with a body (102,202,302,402) that is in contact with the fluid inside a partly enclosed space (101,201,301,401). Furthermore, the pressure transients must be allowed to propagate in the fluid. The fluid may be one or more of the following group: primarily water, consolidation fluid, treatment fluid, cleaning fluid, drilling fluid, fracturing fluid and cement.

Claims

1. A method in hydrocarbon recovery operations on a subterranean formation and comprising the application of at least one fluid into the formation, the method comprising: providing at least one partly enclosed space containing a fluid in fluid connection with the fluid in the formation, arranging a body in the partly enclosed space such that a first surface portion of the body is in contact with said fluid and a second surface portion of the body is free of contact with said fluid, the body hereby being positioned so as to separate the fluid filled part of said space from a part of said at least one partly enclosed space without fluid, arranging at least one object outside the fluid filled part of said space and outside said fluid, and inducing pressure transients in said fluid such as to propagate in said fluid and into the formation thereby enhancing a penetration rate of the fluid into the formation, where said pressure transients are induced by a collision process generated by the object falling onto and colliding with said second surface portion of the body such that the collision occurs outside said fluid filled part of said space and outside said fluid without the object making contact with the fluid, wherein said collision process is such that said body is moved about 1 mm or less by said collision process.

2. The method in hydrocarbon recovery operations according to claim 1, where said at least one fluid is provided from at least one reservoir in fluid communication with said partly enclosed space.

3. The method in hydrocarbon recovery operations according to claim 2 further comprising the step of transporting said at least one fluid from said at least one reservoir, by means of at least one fluid transporting apparatus.

4. The method in hydrocarbon recovery operations according to claim 1 where said collision process comprises the object being caused to fall onto said body by means of the gravity force.

5. The method in hydrocarbon recovery operations according to claim 1 where said fluid in the at least one partly enclosed space is a liquid.

6. The method in hydrocarbon recovery operations according to claim 1 where said object collides with said body in air, wherein the air is a fluid different from the first fluid.

7. The method in hydrocarbon recovery operations according to claim 1 further comprising generating a number of said collision processes at time intervals.

8. The method in hydrocarbon recovery operations according to claim 7 where said collision processes are generated at time intervals in the range of 2-20 sec.

9. The method in hydrocarbon recovery operations according to claim 7 comprising the step of generating a first sequence of collision processes with a first setting of pressure amplitude and time between the collisions, followed by a second sequence of collision processes with a different setting of pressure amplitude and time between the collisions.

10. The method in hydrocarbon recovery operations according to claim 9 where said setting of pressure amplitude is changed by changing the mass of said moving object, or changing the velocity of said moving object relative to the velocity of said body.

11. The method in hydrocarbon recovery operations according to claim 1 where said partly enclosed space comprises a first and a second part separated by said body and where the method further comprises filling the first part with fluid prior to said collision process.

12. The method in hydrocarbon recovery operations according to claim 1, where said at least one moving object is connected to at least one wave motion capturing system.

13. The method in hydrocarbon recovery operations according to claim 12, characterized in that said at least one wave motion capturing system comprises at least one floating buoy arranged such as to be set in motion by waves, and where the motion of said at least one floating buoy induces movement of said object, thereby obtaining a nonzero momentum of said object prior to the collision with said body.

14. The method in hydrocarbon recovery operations according to claim 7 where said collision processes are generated at time intervals in the range of 4-10 sec.

15. The method in hydrocarbon recovery operations according to claim 1, wherein said collision process is such that said body moves about 1 mm over a time interval of about 5 ms.

16. The method in hydrocarbon recovery operations according to claim 1, wherein the pressure transients suppress a tendency for blocking and maintain a fluid condition of the subterranean formation.

17. The method in hydrocarbon recovery operations according to claim 1, wherein the pressure transients enhance the area at which the fluid is applied to the subterranean formation.

18. The method in hydrocarbon recovery operations according to claim 1, wherein exchange of fluids is enhanced by pressure transients in the subterranean formation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following different embodiments of the invention will be described with reference to the drawings, wherein:

(2) FIG. 1 shows one possible embodiment of the invention in which pressure transients are added to a fluid, which is subsequently injected into subterranean reservoir formation,

(3) FIG. 2 illustrates another embodiment of the invention in which pressure transients are added to a flowing fluid, which is subsequently injected into subterranean reservoir formation,

(4) FIG. 3 outlines another embodiment of the invention in which an accumulator is introduced in the conduit in order to protect fluid transport apparatus against the effect of the pressure transients,

(5) FIG. 4 shows another embodiment of the invention in which the pressure transients are produced by the energy captured from ocean waves,

(6) FIG. 5 provides a schematic overview of the configuration applied in experimental testing of our inventive method on Berea sandstone cores,

(7) FIG. 6A illustrates the typical shape of a pressure transient obtained during experiments on Berea sandstone cores,

(8) FIG. 6B shows a single pressure transient in greater detail as obtained and measured in the water flooding experiments on a Berea sandstone core,

(9) FIG. 7 is a summary of some of the results obtained in water flooding experiments with and without pressure transients, and

(10) FIG. 8 is a sketch of the experimental set-up for a core flooding experiment on a Berea sandstone core.

DETAILED DESCRIPTION OF POSSIBLE EMBODIMENTS

(11) The invention of the present patent application is based on employing pressure transients induced by a collision process in hydrocarbon recovery operation.

(12) FIG. 1 shows a possible embodiment of the invention comprising a system with the following components; a hydraulic cylinder 101 with an opening 104, a piston 102, first and second conduits 111, 112 that are both connected to a third conduit 110, first and second check valves 121,122 arranged in first and second conduits 111,112 respectively, and an object 103 which can collide with piston 102. The fluid from reservoir 131 is placed into the subterranean reservoir formation 132, or the fluid from reservoir 131 is replacing hydrocarbons and/or other fluids in the subterranean reservoir formation 132. The pressure transients that are generated when the object 103 collides with the piston 102 propagate at the sound speed into the subterranean reservoir formation 132 along with the fluid originating from the reservoir 131. These pressure transients enhance the penetration rate in the subterranean reservoir formation 132 and suppress any tendency for blockage and maintain the subterranean reservoir formation 132 in a superior flowing condition. This superior flowing condition increases the rate and the area at which the injected fluid from reservoir 131 can be placed into the subterranean reservoir formation 132. Hydrocarbon recovery operations often involves replacement of hydrocarbons in the subterranean reservoir formation 132 with another fluid which in FIG. 1 comes from reservoir 131, and this exchange of fluids is enhanced by the pressure transients propagating into the subterranean reservoir formation 132.

(13) FIG. 2 outlines another embodiment of the invention comprising the same components as the embodiment described in relation to FIG. 1, and additionally comprising a fluid pumping device 240 connected to the conduit system for aiding in the transport of the fluid from the reservoir to the subterranean reservoir formation 232. The system comprises the following components; a hydraulic cylinder 201 with a opening 204, a piston 202, first and second conduits 211, 212 both connected to a third conduit 210, first and second check valves 221,222 arranged in first and second conduits 211,212 respectively, a fluid pumping device 240 connected to the first conduit 211 and a fourth conduit 213, a third check valve 223 arranged in the fourth conduit 213, and an object 203 which can collide with piston 202. The fluid from reservoir 231 is placed into the subterranean reservoir formation 232, or the fluid from reservoir 231 is replacing hydrocarbons and/or other fluids in the subterranean reservoir formation 232. The pressure transients that are generated when the object 203 collides with the piston propagates with the sound speed into the subterranean reservoir formation 232 along with the fluid which is transported by the fluid pumping device 240 from the reservoir 231.

(14) FIG. 3 outlines another embodiment of the inventive methods comprising a system like the systems outlined in relation to FIGS. 1 and 2, additionally comprising an accumulator. The system comprises the following components; a hydraulic cylinder 301 with an opening 304, a piston 302, first and second conduits 311, 312 both connected to a third conduit 310, first and second check valves 321,322 arranged in first and second conduits 311,312 respectively, a fluid pumping device 340 connected to the first conduit 311, a fourth conduit 313, a third check valve 323 arranged in the fourth conduit 313, an accumulator comprising a chamber 350 and a membrane 351 that can separate different fluids in the accumulator which is in fluid communication with the first conduit 311 between the first check valve 321 and the fluid pumping device 340, and an object 303 which can collide with piston 302. The fluid from reservoir 331 is placed into the subterranean reservoir formation 332, or the fluid from reservoir 331 is replacing hydrocarbons and/or other fluids in the subterranean reservoir formation 332. The pressure transients that are generated when the object 303 collides with the piston propagates with the sound speed into the subterranean reservoir formation 332 along with the fluid which is transported by the fluid pumping device 340 from the reservoir 331. The accumulator arranged between the pumping device 340 and the cylinder 301 where the pressure transients are generated acts to dampen out and accumulate any pressure transients travelling through that part of the system of conduits and thereby not aiding in the hydrocarbon recovery operation.

(15) FIG. 4 outlines another embodiment of the invention comprising a system as described previously in relation to FIGS. 1-3, and where the object 403 caused to collide with the piston 402 is set in motion by ocean waves 460. The system comprises the following components; a hydraulic cylinder 401 with an opening 404, a piston 402, first and second conduits 411, 412 that are both connected to a third conduit 410, first and second check valves 421,422 arranged in first and second conduits 411,412 respectively, a fluid pumping device 440 connected to the first conduit 411, a fourth conduit 413, a third check valve 423 arranged in the fourth conduit 413, an accumulator comprising a chamber 450 and a membrane 451 that can separate different fluids in the accumulator which is in fluid communication with the first conduit 411 between the first check valve 421 and the fluid pumping device 440, a floating buoy 405 connected to a object 403, a guiding installation 406 that prevents the object 403 from drifting horizontally relative to the piston 402, the object 403 being able to collide with piston 402. The system may optionally be configured without any pumping device 440. Likewise, the system may be configured without any accumulator or with further accumulators placed at other locations. The accumulator(s) may likewise be of other types than the one shown here with a membrane. The floating buoy 405 is set in motion by the ocean waves 460, whereas the guiding installation 406 guides the object 403 so that a significant part of the momentum of the object 403 for the collision process with the piston 402 may be provided by the ocean waves 460. The fluid from reservoir 431 is placed into the subterranean reservoir formation 432, or the fluid from reservoir 431 is replacing hydrocarbons and/or other fluids in the subterranean reservoir formation 432. The pressure transients that are generated when the object 403 collides with the piston propagates with the sound speed into the subterranean reservoir formation 432 along with the fluid which is transported by the fluid pumping device 440 from the reservoir 431.

(16) FIG. 5 is an overview of a configuration applied in flooding experiments on Berea sandstone cores, where the following components are employed; a hydraulic cylinder 501 connected to two pipelines 510 and 511, a piston 502, an object 503, a fluid pumping device 540 connected to the pipelines 511 and 513, a reservoir 531 containing the salt water applied in the core flooding experiments, a container 532 where a Berea sandstone core plug is installed and which is connected to the pipelines 510 and 512, a back valve 522 connected to two pipelines 512 and 514, a tube 533 placed essentially vertically and applied for measuring the volume of oil recovered during the core flooding experiments, a pipeline 515 connecting the tube 533 to a reservoir 534 where salt water is collected, and finally a check-valve 521.

(17) During the experiments salt water is pumped from the reservoir 531 through a core material placed in the container 532. In these experiments Berea sandstone cores have been used with different permeabilities of about 100-500 mDarcy, which prior to the experiments were saturated with oil according to standard procedures. The oil recovered from the flooding by the salt water will accumulate at the top of the tube 533 during the experiments, and the volume of the salt water collected in the reservoir 534 is then equal to the volume transported from the reservoir 531 by the pumping device 540. The more specific procedures applied in these experiments follow a standard method on flooding experiments on Berea sandstone cores.

(18) The pipeline 511 is flexible in order to accommodate any small volume of fluid which may be accumulated in the pipeline during the collision process between the piston 502 and the object 503 due to the continuous transporting of fluid by the pumping device 540.

(19) The piston 502 is placed in the cylinder 501 in a bearing and the cylinder space beneath the piston is filled with fluid. In the experiments a hydraulic cylinder for water of about 20 ml is used. The total volume of salt water flowing through the container 532 was seen to correspond closely to the fixed flow rate of the pumping device. Thus, the apparatus comprising the hydraulic cylinder 501, the piston 502 and the object 503 contribute only insignificantly to the transport of salt water in these experiments. The collision of the object with the piston occurs during a very short time interval. Therefore, the fluid is not able to respond to the high impact force by a displacement resulting in a increase of the flow and thus altering of said fixed flow rate. Rather, the fluid is compressed by the impact and the momentum of the piston is converted into a pressure transient. Hence, any motion of the piston 502 during the collision process is believed to relate to a compression of the fluid beneath the piston and not due to any net displacement of fluid out of the hydraulic cylinder 501.

(20) The pressure transients during the performed experiments were generated by an object 503 with a weight of 5 kg raised to a height of 17 cm and caused to fall onto the cylinder thereby colliding with the piston 502 at rest. The hydraulic cylinder 501 used had a volume of about 20 ml and an internal diameter of 25 mm corresponding to the diameter of the piston 502. The apparatus for performing the collision process is illustrated in FIG. 8.

(21) Experiments were made with pressure transients generated with an interval of about 6 sec (10 impacts/min) over a time span of many hours.

(22) The movement of the piston 502 caused by the collisions was insignificant compared to the diameter of the piston 502 and the volume of the hydraulic cylinder 501 resulting only in a compression of the total fluid volume which may be deducted from the following. The volume of the hydraulic cylinder 501 is about 20 ml and the fluid volume in the Berea sandstone core in the container is about 20-40 ml (cores with different sizes were applied). The total volume which can be compressed by the object 503 colliding with the piston 502 is therefore about 50-100 ml (including some pipeline volume). A compression of such volume with about 0.5% (demanding a pressure of about 110 Bar since the bulk modulus of water is about 22 000 Bar) represents a reduction in volume of about 0.25-0.50 ml corresponding to a downward displacement of the piston 502 with approximately 1 mm or less. Thus the piston 502 moves about 1 mm over a time interval of about 5 ms during which the pressure transients could have propagated about 5-10 m. This motion is insignificant compared with the diameter of the piston 502 and the volume of the hydraulic cylinder 501.

(23) FIG. 6A show the pressure p in the fluid measured at the inlet of the container 532 as a function of time t for a duration of one of the performed experiments. The pressure transients were generated by an object 503 with a weight of 5 kg caused to fall onto the piston from a height of 17 cm. Collisions (and hence pressure transients) were generated at time intervals 600 of approximately 6 s, i.e. a new collision was generated approximately every 6.sup.th second. By the above mentioned means were generated pressure amplitudes in the range of at least 70-180 Bar or even higher, since the pressure gauges used in the experiments could only measure up to 180 Bar. In comparison, an object with a mass of about 50 kg (with a weight of about 500 N) would be needed in order to push or press (not hammer) down the piston in order to generate a static pressure of only about 10 Bar. The fluid state (turbulence etc.) and the conditions in the Berea Sandstone are never the same for all impacts as the conditions change during the cause of the experiment. The system, therefore, changes after each impact, which may be the reason for the variations between the measured pressure transients.

(24) A single pressure transient is shown in greater detail in FIG. 6B which is also illustrating the typical shape of a pressure transient as obtained and measured in the laboratory water flooding experiments on a Berea sandstone core. Notice the amplitude of about 170 Bar (about 2500 psi), and that the width 601 of each of the pressure transients in these experiments is approximately or about 5 ms, thereby yielding a very steep pressure front and very short raise and fall time. In comparison, pressure amplitudes obtained by pressure pulsing caused by rapid opening of a valve have widths of several seconds and often less than 10 Bar.

(25) FIG. 7 is a summary of some of the results obtained in the water flooding experiments on Berea sandstone cores described previously. Comparative experiments have been conducted for different flooding speeds, and without (noted ‘A’) and with pressure transients (noted ‘B’), and are listed in the table of FIG. 7 below one another.

(26) The experiments performed without pressure transients (noted ‘A’) were performed with a static pressure driven fluid flow where the pumping device 540 was coupled directly to the core cylinder 532. In other words the hydraulic cylinder 501 including the piston 502 and object 503 was disconnected or bypassed. The same oil type of Decane was used in both series of experiments.

(27) The average (over the cross section of the core plug) flooding speed (in μm/s) is given by the flow rate of the pumping device. In all experiments, except 36, the apparatus for generating pressure transients contribute insignificantly to the total flow rate and thus the flooding speed, which is desirable since a high flooding speed could result in a more uneven penetration of the injected water, and thus led to an early water breakthrough. In the experiment 36 the experimental set-up further comprised an accumulator placed between the hydraulic cylinder 501 and the fluid pumping device 540, which is believed to have given an additional pumping effect causing the high flooding speed of 30-40 μm/s as reported in the table. As seen from the experimental data, application of pressure transients to the water flooding resulted in a significant increase in the oil recovery rate in the range of approximately 5.3-13.6% (experiments 2 and 4, respectively), thus clearly demonstrating the potential of the proposed hydrocarbon recovery method according to the present invention.

(28) FIG. 8 is a sketch showing the apparatus used for moving the object applied in the collision process in the experiments on Berea sandstone cores, and showing the experimental set-up as applied on the core flooding experiment on a Berea sandstone core as described in the previous.

(29) The pressure transients are here generated by an impact load on the piston 502 in the fluid filled hydraulic cylinder 501. A mass 801 is provided on a vertically placed rod 802 which by means of a motor 803 is raised to a certain height from where it is allowed to fall down onto and impacting the piston 502. The impact force is thus determined by the weight of the falling mass and by the falling height. More mass may be placed on the rod and the impacting load adjusted. The hydraulic cylinder 501 is connected via a tube 511 (not shown in FIG. 8) to a fluid pump 540 which pumps salt water via a tube 804 from a reservoir (not shown) through the cylinder and through an initially oil saturated Berea sandstone core placed in the container 532. Pressure was continuously measured at different positions. A check valve 521 (not shown) between the pump and the cylinder ensures a one-directional flow. When having passed the Berea sandstone core, the fluid (in the beginning the fluid is only oil and after the water break trough it is almost only salt water) is pumped to a tube for collecting the recovered oil and a reservoir for the salt water as outlined in FIG. 5.