Method for judging influence of wettability difference on selective filling of crude oil

Abstract

The application discloses a method for judging influence of wettability difference on selective filling of crude oil, selects a plurality of natural oil-bearing core samples with different permeability, prepares two same core columns for each group, processes one core column as water wettability, processes the other core column as oil wettability, then tests porosity, permeability and oil saturation of each core column; places the core columns in parallel displacement devices to process saturated formation water; adopts steady-state filling mode to simulate crude oil filling, records filling pressure and corresponding cumulative crude oil filling content of each core column; repeatedly processes the water-wet core columns as water wettability, adopts single steady-state filling mode to simulate crude oil filling and takes the water-wet core columns as a control group, records filling pressure and corresponding cumulative crude oil filling content, and prepares corresponding curve graphs, and analyzes crude oil filling behavior under the condition that the difference wettability core bodies exist simultaneously. The application can characterize whether the crude oil selectively fills under the condition that the difference wettability core bodies exist simultaneously.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration technology, and in particular to a method for judging the influence of wettability differences on crude oil selective charging. Background Technology

[0002] Secondary migration of oil and gas refers to the various migrations of oil and natural gas after they enter transport channels. These channels primarily include faults, unconformities, and sand bodies. Within sand bodies, migration mostly occurs within limited dominant channels, meaning it always happens along the path of least resistance, typically the macroporosity and permeability sections of the sand body. Statistics show that over 70% of global oil reservoirs are located along the "dominant channels" of selective crude oil migration. Therefore, studying and identifying dominant migration channels is a crucial aspect of oil reservoir exploration.

[0003] The simulation methods involved in the study of dominant migration channels mainly include physical simulation and numerical simulation. The main controlling factors for the formation of dominant migration channels are twofold: ① the macroscopic perspective of maximum dynamics, which posits that oil, under the influence of buoyancy, first migrates towards its top surface and then adjusts laterally; ② the microscopic perspective of minimum resistance, which states that oil always migrates along the channel with the least capillary resistance. Based on these two perspectives, physical simulations can be categorized into sandbox simulation and core filling simulation. The scale of sandbox simulation limits its ability to serve as a simplified representation of macroscopic oil and gas migration and cannot accurately reflect the objective conditions in situ underground. While core filling simulation cannot reflect macroscopic oil and gas migration phenomena, it is highly effective for studying the force balance of crude oil injected into the core at the microscopic scale.

[0004] Whether crude oil can be charged into a core is essentially a matter of force balance. The driving forces for charging mainly include the overpressure from hydrocarbon generation, the pressure difference between the source rock and the reservoir, and buoyancy; the resistance to charging mainly includes capillary force and friction (generally negligible). When the charging force is constant, the dominant migration channel is essentially the one with the least migration resistance, which can be considered as the one with the least capillary force, influenced by a combination of pore throat radius and wettability.

[0005] Previous charging simulations, using multiple charging experiments on a single core, have demonstrated that the existence of dominant migration channels results in non-uniform selective charging of crude oil during the initial injection, with subsequent charging exhibiting memory selective charging along the path of the initial injection. It was suggested that the initial injection follows seepage channels with large pore-throat radii, while the memory selective charging during subsequent injections is due to changes in the wettability of these channels (from hydrophilic to oleophilic). However, the presence of both large pore-throat radius and oleophilicity in subsequent charging cannot be clearly distinguished by a single core's charging experiment, nor can it be determined whether these two factors influence crude oil charging behavior individually or whether there is a mutual influence between them. Furthermore, sedimentary strata are objectively heterogeneous; the coexistence of multiple pore-throat radii and wettability rock systems is an objective fact of in-situ strata, which cannot be effectively characterized by charging simulations based solely on a single core. Specifically, when multiple core systems coexist, questions arise regarding whether memory selective charging exists; at what physical properties will memory selective charging occur; and at what charging pressure will the memory selective charging pattern be lost. The answers to the above questions are of great theoretical significance and practical application value for deepening the theory of reservoir geology. Summary of the Invention

[0006] The purpose of this invention is to provide a method for judging the influence of wettability differences on selective crude oil charging, so as to solve the problems existing in the prior art. By adjusting the experimental charging pressure, the method characterizes whether crude oil is selectively charged under the condition that cores with different wettability exist simultaneously.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] This invention provides a method for determining the impact of wettability differences on crude oil selective charging, comprising the following steps:

[0009] S1. Select multiple groups of natural oil-bearing core samples with different permeabilities. For each type of core sample with different permeabilities, prepare two core columns of the same size. Two core columns with the same permeability are set as a group. At the same time, mix experimental water and oil to simulate actual formation water and crude oil.

[0010] S2. In S1, one core column from each group of core columns with different permeabilities was selected for oil washing, drying, and wettability testing to ensure that the core wettability was water wettability. Then, another core column from each group of core columns with different permeabilities was subjected to nuclear magnetic resonance centrifugation and drying to ensure that the core wettability was oil wettability. Finally, the porosity, permeability, and oil saturation of each core column were tested again.

[0011] S3. Place the two core columns with the same permeability but different wettability from S2 into a parallel displacement device and treat them with saturated formation water.

[0012] S4. For the two core columns with the same permeability but different wettability in S3, crude oil charging simulation was carried out using steady-state charging method, and the charging pressure and corresponding cumulative crude oil charging content of each core column were recorded.

[0013] S5. For the core column with water wettability in S4, repeat the oil washing, drying and wettability operation in S2 to ensure that the core wettability is water wettability. Use a single non-parallel steady-state charging method to simulate crude oil charging as a control group. Record the charging pressure and corresponding cumulative crude oil charging content of each group of core columns with different permeability.

[0014] S6. The charging pressure and corresponding cumulative crude oil charging content obtained in S3 and S4 are sorted out, and a curve of cumulative crude oil charging content as a function of charging pressure is generated to analyze the crude oil charging behavior under the condition of simultaneous presence of differentially wettable cores.

[0015] Preferably, in S1, one sample is selected for each order of magnitude of the permeability from 0.1 mD to 100 mD.

[0016] Preferably, the core column is cylindrical, with a diameter of 2.5 cm and a length of 5 cm.

[0017] Preferably, the parallel displacement device in S3 includes a displacement pump, a data acquisition module, and two parallel clamping simulation systems. One end of each clamping simulation system is connected to the same displacement pump, and each clamping simulation system has a pressure sensor at both ends. Each pressure sensor is electrically connected to the data acquisition module. Each clamping simulation system is used to place different core columns with the same permeability. The displacement pump is used to fill the clamping simulation system with water and oil. Each clamping simulation system is independent of each other and can be turned on or off individually.

[0018] Preferably, the clamping simulation system includes a core holder, a confining pressure system, a nitrogen cylinder, and a glass tube gauge. The core holder is used to clamp the core column. One end of the core holder is connected to the displacement pump via a filling pipeline, and a filling switch valve is provided on the filling pipeline. The other end of the core holder is connected to a back pressure valve via a discharge pipeline, and a discharge switch valve is provided on the discharge pipeline. The back pressure valve is also connected to the glass tube gauge, and the back pressure valve is connected to the nitrogen cylinder via a back pressure pipeline, and a back pressure switch valve is provided on the back pressure pipeline. The confining pressure system is connected to the interior of the core holder, and a confining pressure switch valve is provided between the confining pressure system and the core holder.

[0019] Preferably, in the same clamping simulation system, one pressure sensor is located between the filling switch valve and the core holder, and the other pressure sensor is located between the discharge switch valve and the back pressure valve.

[0020] Preferably, the displacement pump is a micro-metering displacement pump.

[0021] Preferably, the data acquisition module is a computer acquisition system.

[0022] The present invention achieves the following technical effects compared to the prior art:

[0023] 1. This invention simulates the synchronous injection of crude oil with different wettability under the same pressure system, using a parallel injection experiment, which has the advantage of allowing for direct comparison.

[0024] 2. This invention simulates the mutual influence of the simultaneous existence of crude oil injection channels with different wettability, which is consistent with the objective fact of the heterogeneity of sedimentary strata and can better reflect the hypothesis of whether there is a selective oil wetting channel during the crude oil injection process.

[0025] 3. This invention simulates the effect of different wettability on crude oil charging methods under different permeability and charging power. It has the advantage of being able to verify at what level of physical properties will form memory selective charging and at what level of charging pressure will the memory selective charging method be lost. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A flowchart of the method for determining the influence of wettability differences on crude oil selective charging provided by the present invention;

[0028] Figure 2 This is a schematic diagram of the core column preparation in S1 of the present invention;

[0029] Figure 3 This is a schematic diagram of the parallel displacement device in this invention;

[0030] Figure 4 This is a graph showing the cumulative oil volume as a function of filling pressure in this invention.

[0031] In the diagram: 1-Displacement pump, 2-Injection switch valve, 3-Pressure sensor, 4-Core holder, 5-Containing pressure system, 6-Containing pressure switch valve, 7-Discharge switch valve, 8-Glass tube gauge, 9-Back pressure valve, 10-Nitrogen cylinder, 11-Back pressure switch valve, 12-Data acquisition module. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The purpose of this invention is to provide a method for judging the influence of wettability differences on selective crude oil charging, so as to solve the problems existing in the prior art. By adjusting the experimental charging pressure, it can characterize whether crude oil is selectively charged under the condition that cores with different wettability exist simultaneously.

[0034] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] like Figures 1-4 As shown, this invention provides a method for judging the influence of wettability differences on selective crude oil charging. It involves conducting parallel displacement experiments using a parallel displacement device, selecting sample points with different permeabilities, and preparing parallel sample points for both oil-wetted and water-wetted samples for each sample for comparative analysis. These are then connected in parallel within the parallel displacement device. By adjusting the experimental charging pressure, the method characterizes whether crude oil is selectively charged under the condition of simultaneous presence of cores with different wettability. The specific steps include:

[0036] S1. Core column preparation and formation water / crude oil mixing, specifically including:

[0037] S1a. Based on core samples from well drilling in mature oilfields, with basic physical property data (permeability, oil saturation), oil-bearing sample points are selected with permeability as a parameter, and one sample is selected in each order of magnitude from 0.1mD to 100mD, for a total of four samples, thus obtaining four groups of core samples with different permeabilities.

[0038] S1b. For each core sample, drill two core columns of the same size along the direction perpendicular to the bedding plane or the long axis of the core sample. Two core columns with the same permeability are set as a group. The length of the core column is 5cm and the diameter is 2.5cm. The size can be adjusted according to actual needs.

[0039] S1c. The formation water ratio is based on the actual formation water salinity of the oilfield, the water type is NaHCO3, and the density is 1.02 g / mL; the crude oil ratio has a viscosity of 44 MPa·s and a density of 0.75 g / mL, simulating the actual formation water and crude oil.

[0040] S2. Core column wettability pretreatment, specifically including:

[0041] S2a. Select one core column from the core samples of each permeability for oil washing treatment. After drying, test the porosity, permeability and quality of the dried sample. During the oil washing process, surfactants can be added to eliminate the oil wettability of the core column. Wettability test is performed to ensure that the core column is only wetted by water.

[0042] S2b. Select another core column from the core samples of each permeability, perform nuclear magnetic resonance centrifugation to remove movable oil and water, and dry the sample to test the porosity, permeability and mass.

[0043] S2c. Retest the porosity, permeability, and oil saturation of the core samples;

[0044] S3. Treatment of core-saturated formation water, specifically including:

[0045] S3a. Check the sealing performance of the parallel displacement device and adjust the confining pressure pump to ensure that the experimental confining pressure is always 3 MPa higher than the charging pressure.

[0046] S3b. If core columns with different wettability from the same group of core samples are placed into each core holder 4, then wettability can be considered as the only variable, and the oil and gas charging behavior of core columns with different wettability under the same charging conditions can be simulated.

[0047] S3c. Vacuum the core holder 4, close the oil injection system, open the water injection system, and use the high-pressure water injection system to displace the air in the core column. When no gas is discharged from the outlet, the core can be considered saturated with water.

[0048] S4. Steady-state crude oil charging experiment simulation, specifically including:

[0049] S4a. Close the water injection system, open the oil injection system, set 1MPa as the initial driving pressure for injection, and monitor the oil flow rate from the outlet end of the core holder 4 in 2h time units.

[0050] S4b. When the pressure difference between the two ends of the core holder 4 is stable and the cumulative amount of crude oil injected remains unchanged, increase the driving pressure in units of 1 MPa and repeat the simulation of the crude oil injection process in steady state mode.

[0051] S4c. Until the driving pressure is increased further, the cumulative amount of crude oil injected into the outlet end of the oil-wetted core holder 4 remains unchanged, so the oil-wetted sample injection system is shut down.

[0052] S4d. Observe the crude oil charging phenomenon of water-wetted sample. When the pressure difference between the two ends of the core holder 4 is stable and the cumulative amount of crude oil charged does not change, increase the driving pressure in units of 1 MPa and repeat the simulation of the crude oil charging process in steady state mode until the driving pressure continues to increase and the cumulative amount of crude oil charged at the outlet end of the water-wetted core holder 4 still does not change. Then, shut down the oil-wetted sample charging system.

[0053] Then S3 and S4 were repeated for each group of core samples;

[0054] S5. Control group: Steady-state filling simulation experiments were performed and recorded using the original method, specifically including:

[0055] S5a. After S4 is completed for each group of core columns, select the core columns in each group that have been treated with water and repeat S2 and S3.

[0056] S5b. A single non-parallel filling method is used, the same as S4, as a control group;

[0057] S6. Experimental data processing, statistics, and analysis, specifically including:

[0058] S6a. Compile the charging pressure and corresponding cumulative charging amount for each group of experiments;

[0059] S6b. Create a curve showing the cumulative amount of oil injected as a function of injection pressure;

[0060] S6c. Conduct the determination of the dominant channel for crude oil charging. The parallel water-wetted core column is designated as number 1, the parallel oil-wetted core column as number 2, and the water-wetted core column in the separate comparison group as number 0. The determination method is as follows:

[0061] ① Section A: Core samples with a permeability of 100 mD: The curves A1 and A2 are almost identical, indicating that both can reach the maximum cumulative crude oil volume (2.7 mL) under low charging pressure (1 MPa), which is considered as oil saturation; at the same time, the A0 control group can also prove that the charging behavior of a water-wetted core column alone is similar to the charging behavior of a differentially wetted charging channel, indicating that there is no dominant migration channel when oil-wetted and water-wetted cores coexist under 100 mD physical property conditions.

[0062] ②Section B: Core samples with a permeability of 10 mD: The curves B1 and B2 are nearly identical, indicating that both can reach the maximum cumulative crude oil volume (1.8 mL) under low charging pressure (2 MPa), which is considered as oil saturation. However, the two curves show different trends in their growth stages. The oil-wetted core column (B2) shows a high-to-low growth rate of cumulative crude oil volume in each pressure range, with the curve showing an upward convex shape. In contrast, the water-wetted core column (B1) shows a low-to-high growth rate of cumulative crude oil volume in each pressure range, with the curve showing a downward concave shape. This indicates that under the same permeability (10 mD), the difference in wettability has a significant impact on the crude oil charging rate, initially demonstrating the selectivity in crude oil charging rate. At the same time, the charging curve of the B0 control group, which is water-wetted alone, is between B1 and B2, indicating that the difference in crude oil charging behavior is more obvious when the differential wettability channels are present simultaneously.

[0063] ③ Section C: For core samples with a permeability of 1 mD: the charging curves of C0, C1, and C2 show significant differences, but the maximum cumulative crude oil charging values ​​are similar. C2 oil-wetted core column shows crude oil charging at 4 MPa, and after the C2 charging system is shut down at 12 MPa, C1 water-wetted core column immediately shows crude oil charging, and the maximum cumulative crude oil charging value can be reached without pressurization. This indicates that under 1 mD permeability conditions, oil-wetted core column is the dominant transport channel compared to water-wetted core column, and crude oil is selectively injected through oil-wetted core column. At the same time, through the C0 control group, it can be found that the starting charging pressure of water-wetted core column alone is 6 MPa, indicating that without parallel oil-wetted core columns, water-wetted core columns can charge at a charging pressure of 6 MPa, which is much lower than the 12 MPa starting charging pressure in the C1 parallel case.

[0064] ④ Section D: Core samples with a permeability of 0.1 mD: The charging curves of D0, D1, and D2 are similar to those in Section C, which also indicates that under the condition of 0.1 mD permeability, oil-wetted core columns are the dominant migration channel compared to water-wetted core columns, and crude oil is selectively injected through oil-wetted core columns. Furthermore, by comparing the starting charging pressure difference between C2 and C0 (3 MPa) and the starting charging pressure difference between D2 and D0 (2 MPa), it can be found that when the permeability decreases by an order of magnitude, the starting charging pressure of a single oil-wetted core column (No. 2) is 1 MPa lower than that of a single water-wetted sample (No. 0). This indicates that the lower the permeability, the more obvious the selective crude oil charging behavior caused by the difference in wettability is, and the easier it is to form a dominant migration channel.

[0065] Specifically, the parallel displacement device in S3 includes a displacement pump 1, a data acquisition module 12, and two parallel clamping simulation systems. One end of each clamping simulation system is connected to the same displacement pump 1, and each clamping simulation system has a pressure sensor 3 at both ends. Each pressure sensor 3 is electrically connected to the data acquisition module 12. Each clamping simulation system is used to place different core columns with the same permeability. Through the parallel clamping simulation systems, the synchronous injection of crude oil with the same sample and different wettability under the same pressure system is simulated, which has the advantage of intuitive comparison. The displacement pump 1 is used to fill the clamping simulation system with water and oil. Each clamping simulation system is independent of each other and can be turned on or off individually.

[0066] The clamping simulation system includes a core clamp 4, a confining pressure system 5, a nitrogen cylinder 10, and a glass tube gauge 8. The core clamp 4 is used to clamp the core column. One end of the core clamp 4 is connected to a displacement pump 1 via a filling pipeline, and the filling pipeline is equipped with a filling switch valve 2, which can control the filling of the core column with water or oil, or stop the filling process. The other end of the core clamp 4 is connected to a back pressure valve 9 via a discharge pipeline, and the discharge pipeline is equipped with a discharge switch valve 7. The back pressure valve 9 is also connected to the glass tube gauge 8, which controls the filling of the core column with water or oil, or stops the filling process. Positioned at the outlet end of the core column, valve 8 measures the volume of water displaced by the injected crude oil. It also measures the excess oil injected after the core column is saturated with oil; the difference between this and the injected volume represents the amount of saturated crude oil injected into the core column. Backpressure valve 9 is connected to nitrogen cylinder 10 via a backpressure pipeline. Valve 9 controls the pressure and flow rate of the passing fluid. A backpressure switch valve 11 is installed on the backpressure pipeline. The confining pressure system 5 is internally connected to the core holder 4, and a confining pressure switch valve 6 is installed between the confining pressure system 5 and the core holder 4. The installation of these valves allows for checking the airtightness of the entire apparatus before the experiment begins and for controlling water filling, oil filling, and confining pressure application as needed during the experiment.

[0067] In the same clamping simulation system, one pressure sensor 3 is located between the filling switch valve 2 and the core clamp 4, and another pressure sensor 3 is located between the discharge switch valve 7 and the back pressure valve 9. Thus, by setting each pressure sensor 3, real-time monitoring of the inlet and outlet pressures of the core clamp 4 can be achieved.

[0068] Displacement pump 1 is a micro-metering displacement pump.

[0069] Data acquisition module 12 is a computer-based data acquisition system.

[0070] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for determining the influence of wettability differences on crude oil selective charging, characterized in that: Includes the following steps: S1. Select multiple groups of natural oil-bearing core samples with different permeabilities. For each type of core sample with different permeabilities, prepare two core columns of the same size. Two core columns with the same permeability are set as a group. At the same time, mix experimental water and oil to simulate actual formation water and crude oil. S2. In S1, one core column from each group of core columns with different permeabilities was selected for oil washing, drying, and wettability testing to ensure that the core wettability was water wettability. Then, another core column from each group of core columns with different permeabilities was subjected to nuclear magnetic resonance centrifugation and drying to ensure that the core wettability was oil wettability. Finally, the porosity, permeability, and oil saturation of each core column were tested again. S3. Place the two core columns with the same permeability but different wettability from S2 into a parallel displacement device and treat them with saturated formation water. S4. For the two core columns with the same permeability but different wettability in S3, crude oil charging simulation was carried out using steady-state charging method, and the charging pressure and corresponding cumulative crude oil charging content of each core column were recorded. S5. For the core column with water wettability in S4, repeat the oil washing, drying and wettability operation in S2 to ensure that the core wettability is water wettability. Use a single non-parallel steady-state charging method to simulate crude oil charging as a control group. Record the charging pressure and corresponding cumulative crude oil charging content of each group of core columns with different permeability. S6. The charging pressure and corresponding cumulative crude oil charging content obtained in S3 and S4 are sorted out, and a curve of cumulative crude oil charging content as a function of charging pressure is generated to analyze the crude oil charging behavior under the condition of simultaneous presence of differentially wettable cores.

2. The method for determining the influence of wettability differences on crude oil selective charging according to claim 1, characterized in that: In S1, one sample is selected for each order of magnitude of permeability from 0.1 mD to 100 mD.

3. The method for determining the influence of wettability differences on crude oil selective charging according to claim 1, characterized in that: The core column is cylindrical, with a diameter of 2.5 cm and a length of 5 cm.

4. The method for determining the influence of wettability differences on crude oil selective charging according to claim 1, characterized in that: The parallel displacement device in S3 includes a displacement pump, a data acquisition module, and two clamping simulation systems arranged in parallel. One end of each clamping simulation system is connected to the same displacement pump, and each clamping simulation system has a pressure sensor at both ends. Each pressure sensor is electrically connected to the data acquisition module. Each clamping simulation system is used to place different core columns with the same permeability. The displacement pump is used to fill the clamping simulation system with water and oil. Each clamping simulation system is independent of each other and can be turned on or off individually.

5. The method for determining the influence of wettability differences on crude oil selective charging according to claim 4, characterized in that: The clamping simulation system includes a core holder, a confining pressure system, a nitrogen cylinder, and a glass tube gauge. The core holder is used to clamp the core column. One end of the core holder is connected to the displacement pump via a filling pipeline, and a filling switch valve is provided on the filling pipeline. The other end of the core holder is connected to a back pressure valve via a discharge pipeline, and a discharge switch valve is provided on the discharge pipeline. The back pressure valve is also connected to the glass tube gauge, and the back pressure valve is connected to the nitrogen cylinder via a back pressure pipeline, and a back pressure switch valve is provided on the back pressure pipeline. The confining pressure system is connected to the interior of the core holder, and a confining pressure switch valve is provided between the confining pressure system and the core holder.

6. The method for determining the influence of wettability differences on crude oil selective charging according to claim 5, characterized in that: In the same clamping simulation system, one pressure sensor is located between the filling switch valve and the core holder, and the other pressure sensor is located between the discharge switch valve and the back pressure valve.

7. The method for determining the influence of wettability differences on crude oil selective charging according to claim 4, characterized in that: The displacement pump is a micro-metering displacement pump.

8. The method for determining the influence of wettability differences on crude oil selective charging according to claim 4, characterized in that: The data acquisition module is a computer-based data acquisition system.

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