An unconventional core oil saturation method and its application

Abstract

The present invention relates to an unconventional core saturation oil method and its application. It mainly solves the problem that the unconventional ultra-low permeability shale core has extremely low permeability and is difficult to be saturated with oil in the background technology. The method comprises: 1. Obtaining the formation pressure of the target reservoir; 2. Injecting the experimental oil into the core at a low speed by pulse injection, and stopping the injection when the core inlet pressure rises to the first pressure setting value; 3. When the core inlet pressure drops, continue to increase the pressure to the first pressure setting value by pulse injection, maintain the stable pressure state for a certain period of time, and then increase the inlet pressure to the next pressure setting value to complete the process of injecting the experimental oil into the core; 4. Repeat steps 2 and 3 for many times until the core inlet pressure reaches the target reservoir formation pressure value, and the saturation is completed. The method realizes the oil saturation step of the unconventional ultra-low permeability shale core to form a "wetting" process, which is conducive to the entry of crude oil into the core.

Description

Technical field:

[0001] The invention relates to the field of indoor physical simulation oil displacement experiments in oil fields, and in particular to a method for saturating unconventional ultra-low permeability shale cores with oil in indoor physical simulation evaluation experiments. Background technology:

[0002] Shale is lamellae-shaped mudstone in oil and gas basins. The biggest difference between shale and conventional oil reservoirs and tight oil reservoirs is that their storage properties vary greatly: conventional oil and gas storage properties are very good, with a permeability of more than 50 millidarcies or even thousands of millidarcies, low permeability oil reservoirs have a permeability of less than 50 millidarcies, and tight oil reservoirs have even lower storage properties, only less than 1 millidarcy. The permeability of shale reservoirs is extremely low and very dense, with an extremely small pore radius. Its permeability can reach microdarcies or even nanodarcies, and it has no natural production capacity at all, just like a piece of iron. However, in fact, the reservoir contains a large amount of oil and gas, especially the sweet spots are rich in oil. After large-scale volume fracturing, industrial production capacity can be obtained. Therefore, it is of great significance to study and explore the development technology of unconventional ultra-low permeability shale.

[0003] At present, the main method for studying unconventional ultra-low permeability shale development technology in the laboratory is the natural imbibition method, which calculates and evaluates the oil production effect of different chemical systems or mining methods based on the amount of oil imbibed from the saturated shale core. Therefore, whether the shale core is fully saturated with oil is a key step in the success of the imbibition experiment, which directly affects the accurate evaluation of the oil production effect of different chemical systems and different mining methods.

[0004] At present, there are few research reports on the method of saturating unconventional ultra-low permeability shale cores with oil. A method that can be used for reference is the indoor low-permeability core high-pressure oil saturation method, which is to use a displacement pump to inject experimental oil into the core, keep the high pressure constant for a period of time, open the core outlet valve to reduce the pressure, and when the core inlet pressure drops to or approaches zero, close the core outlet valve, continue to hold the pressure, and then release the pressure. Repeat this operation many times to complete the core saturation. This method uses high pressure to "squeeze" the experimental oil into the core, and the shale core is extremely dense, like an "iron plate" or a "grindstone". When this method was used during the experiment, it was found that the experimental oil accumulated on the dense shale core inlet end face, blocking the core inlet end face, and it was difficult for subsequent oil samples to enter the core, and the core saturation process could not be completed. Therefore, this method is not suitable for the saturation of unconventional ultra-low permeability shale cores with oil.

[0005] Therefore, seeking a method to solve the oil saturation problem of unconventional ultra-low permeability shale cores is one of the key technologies to accurately evaluate the imbibition effects of different chemical systems and different production methods. Summary of the invention:

[0006] The present invention aims to overcome the problem in the prior art that when the unconventional ultra-low permeability shale core is saturated with oil, the experimental oil is difficult to enter the core and the core cannot be saturated with oil, and provide an unconventional ultra-low permeability shale core saturation method. The core saturation method, by introducing the concepts of pulse injection disturbance, pressure increase and pressure decrease creep, and gradual gradient increase from low pressure to high pressure, realizes the unconventional ultra-low permeability shale core saturation step to form an "infiltration" process, solves the problem of crude oil blocking the core inlet end face, and is conducive to the entry of crude oil into the core.

[0007] An object of the present invention is to provide an unconventional core saturation oil method, comprising the following steps:

[0008] Step 1: obtaining the target reservoir formation pressure based on the target reservoir conditions;

[0009] Step 2: Prepare for the saturated oil experiment;

[0010] Step 3: Inject the experimental oil into the core at a low speed by pulse injection, and stop the injection when the core inlet pressure rises to the initial pressure setting value;

[0011] Step 4, open the core outlet valve, when the core inlet pressure drops, continue to use pulse injection to increase the pressure to the first pressure setting value, maintain the steady pressure state for a certain period of time, and then increase the inlet pressure to the next pressure setting value, completing the process of injecting experimental oil into the core;

[0012] Step 5, repeat steps 3 and 4 multiple times, and the pressure setting value each time is the pressure setting value after the last inlet pressure increase plus the preset value, until the core inlet pressure is increased to the target reservoir formation pressure value, and saturation is completed.

[0013] Preferably, the pulse injection is achieved by a pulse generator;

[0014] and / or

[0015] The pulse generator is a pulse injection pump or a single-cylinder plunger pump;

[0016] and / or

[0017] The low speed injection rate using the pulse injection method is 0.001-0.1 ml / min.

[0018] Preferably, the lower the injection speed of the pulse injection, the more frequent the tiny pulse disturbances caused on the core inlet end face, which is more conducive to the experimental oil entering the core.

[0019] Preferably, step 4 opens the core outlet valve and collects the experimental oil at the core outlet end at the same time.

[0020] Preferably, when the amplitude of the drop in the core inlet pressure in step 4 reaches half of the sum of the previous pressure setting value and the current pressure setting value, pulse injection is continued to be used to increase the pressure to the current pressure setting value.

[0021] Preferably, maintaining the steady-pressure state for a certain period of time means that within a certain pressure setting value, the pressure reduction / increase operation in step 4 is repeated multiple times; this is to utilize the periodic pressure reduction / increase fluctuation of the core inlet pressure to form a "creeping" migration and flow process of the crude oil inside the core, which is beneficial to the advancement and diffusion of the crude oil inside the core. The more times the operation is repeated, the better the saturation effect. Preferably, the number of repeated operations is 3-5 times.

[0022] Preferably, the first pressure setting value is gradually increased to a target reservoir formation pressure value.

[0023] Preferably, the pressure gradient from the initial pressure setting value to the target reservoir formation pressure value is 1-2 MPa.

[0024] Preferably, the oil saturation experiment is implemented by physically simulating a core oil saturation device in a laboratory.

[0025] Preferably, the laboratory physical simulation core saturated oil device includes a core clamp, the core clamp inlet pipeline is connected to a pulse generator and an oil sample container tank, the pulse generator is a single-cylinder plunger pump or a pulse pump, the core clamp inlet pipeline is connected to an inlet pressure gauge and a core inlet valve; the core clamp outlet pipeline is connected to a core outlet valve and a collecting container; the middle part of the core clamp is connected to an annular pressure system, and the annular pressure system includes an annular pressure tank, an annular pressure gauge, and an annular pressure pump.

[0026] Preferably, the experimental preparation process includes:

[0027] Through the laboratory physical simulation of the core saturated oil device, the experimental oil is put into the oil sample container tank, and the pulse injection pump or single-cylinder plunger pump is set to inject the speed throughout the process;

[0028] Turn on the oven heating system and raise the temperature to the target reservoir temperature. Select a natural core and weigh the core dry weight G1. Then put the core into the holder, use the ring pressure pump to increase the ring pressure until the ring pressure gauge shows the set value, and evacuate the core.

[0029] Another object of the present invention is to provide an application of an unconventional core saturated oil method in evaluating unconventional ultra-low permeability shale core saturated oil.

[0030] Compared with the above background technology, the present invention has the following beneficial effects:

[0031] The present invention introduces the concepts of pulse injection disturbance, pressure increase and decrease creep and gradual gradient increase from low pressure to high pressure, so as to realize the oil saturation step of unconventional ultra-low permeability shale core to form a "wetting" process, solve the problem of crude oil blocking the core inlet end face, and facilitate the entry of crude oil into the core. The significant advantages are:

[0032] (1) Pulse injection is used to create frequent and tiny disturbances on the core inlet end face, forming a "wetting" process, which solves the problem of crude oil blocking the core inlet end face and facilitates the entry of crude oil into the core;

[0033] (2) By using the periodic pressure drop / increase fluctuations at the core inlet, the crude oil forms a migration and flow process similar to "creeping" inside the core, which is conducive to the advancement and diffusion of crude oil inside the core;

[0034] (3) By using the method of gradually increasing the pressure from low to high pressure, the swept volume of crude oil inside the core can be gradually expanded, further increasing the oil saturation of the core.

[0035] (4) The method provided by the invention can achieve full oil saturation of unconventional ultra-low permeability shale cores, ensuring the smooth progress of the imbibition experiment and the accuracy of the experimental data, and providing technical support for the research of shale development technology. Description of the drawings:

[0036] The accompanying drawings herein are incorporated into and constitute a part of the specification. These drawings illustrate embodiments consistent with the present invention and, together with the specification, are used to explain the technical solutions of the present invention.

[0037] The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings.

[0038] Attached Figure 1 A flow chart of the unconventional core oil saturation method of the present invention;

[0039] Attached Figure 2 This is a laboratory physical simulation core saturated oil device of the present invention.

[0040] In the figure: 1-pulse generator, 2-oil sample container tank, 3-inlet pressure gauge, 4-core inlet valve, 5-core clamp, 6-core outlet valve, 7-collecting container, 8-ring pressure tank, 9-ring pressure gauge, 10-ring pressure pump. Specific implementation method:

[0041] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical scheme of the present invention is now described in detail. However, it is worth noting that in the detailed description of the present invention below, some specific details are described in detail, but are not limited to these embodiments. For the parts that are not described in detail, those skilled in the art can also fully understand the present invention.

[0042] An unconventional core saturation oil method comprises the following steps:

[0043] Step 1: Obtain the formation pressure of the target reservoir based on the target reservoir conditions; prepare for the saturated oil experiment;

[0044] Step 2: Set the core holder ring pressure to the first ring pressure (Pring1), start the single-cylinder plunger pump to inject at a low speed, and increase the pressure until the core inlet pressure reaches the first pressure setting value (Pring2). 设1 ), when the inlet pressure drops to P1 = P 设1 / 2, continue to use pulse injection to boost the voltage to P 设1 , repeat this operation many times, and dynamically stabilize the pressure for a certain period of time. This operation can keep the core in a "disturbance" state from the end face to the inside, ensuring that the experimental oil can smoothly enter the core.

[0045] The pressure reduction / increase operation is repeated during the time of maintaining the steady pressure state. This is to utilize the periodic pressure reduction / increase fluctuation of the core inlet pressure to form a migration and flow process similar to "creeping" of the crude oil inside the core, which is beneficial to the advancement and diffusion of the crude oil inside the core. The more times the operation is repeated, the better the saturation effect. Preferably, the number of repeated operations is 3-5 times.

[0046] Step 3: Increase the core holder ring pressure to the second ring pressure (P 环2 ), the core inlet pressure is raised to the second pressure setting value (P 设2 ), when the inlet pressure drops to P2=(P 设1 +P 设2 ) / 2, continue to use pulse injection to boost the voltage to P 设2 , repeat this operation several times to dynamically stabilize the voltage for a certain period of time.

[0047] Step 4: Increase the core holder ring pressure to the third ring pressure (P 环3 ), the core inlet pressure is raised to the third pressure setting value (P 设3 ), when the inlet pressure drops to P3=(P 设2 +P 设3 ) / 2, continue to use pulse injection to boost the voltage to P 设3 , repeat this operation several times to dynamically stabilize the voltage for a certain period of time.

[0048] Step n, increasing the core holder ring pressure to the nth ring pressure (P 环n ), the core inlet pressure is raised to the nth pressure setting value (P 设n , if it is the target reservoir pressure), when the inlet pressure drops to P n =(P 设n-1 +P 设n ) / 2, continue to use pulse injection to boost the voltage to P 设n , repeat this operation several times, dynamically stabilize the voltage for a certain period of time, and stop the experiment.

[0049] The unconventional core saturation oil method of the present invention uses the existing core saturation oil method in the background technology and the core saturation oil of the present invention to conduct comparative experiments.

[0050] Experimental preparation:

[0051] like Figure 2 As shown, the laboratory physical simulation core saturated oil device includes a core holder 5, the inlet pipeline of the core holder 5 is connected to the pulse generator 1 and the oil sample container tank 2; the pulse generator 1 is a single-cylinder plunger pump or a pulse pump; the inlet pipeline of the core holder 5 is connected to the inlet pressure gauge 3 and the core inlet valve 4; the outlet pipeline of the core holder 5 is connected to the core outlet valve 6 and the collection container 7; the middle part of the core holder 5 is connected to the annular pressure system, and the annular pressure system includes an annular pressure tank 8, an annular pressure gauge 9, and an annular pressure pump 10.

[0052] The target reservoir has a formation temperature of 80°C and a formation pressure of 11.0 MPa. Two unconventional ultra-low permeability shale cores are selected, wherein the 1# core is subjected to the existing core saturation oil method, and the 2# core is subjected to the core saturation oil method of the present invention, and the core dry weight G1 is weighed using a precision electronic balance (d=0.0001 g). The core is placed in a core holder and then placed in a constant temperature oven.

[0053] The comparison experiment between the existing core saturation oil method and the core saturation oil of the present invention is as follows:

[0054] Comparative example: 1# unconventional ultra-low permeability shale core

[0055] The existing core saturation oil method, operation steps and experimental results are as follows:

[0056] Step 1: Set the ring pressure of core holder 5 to 13.0 MPa.

[0057] Step 2: Turn on the conventional displacement pump to raise the core inlet pressure to 11.0 MPa, stop the pump, and stabilize it for 12 to 24 hours.

[0058] Step 3: Open the core outlet valve 6 to release the pressure for 24 hours, and collect the experimental oil through the collection container 7 at the core outlet.

[0059] Step 4: Turn on the displacement pump again and continue to increase the core inlet pressure to 11.0 MPa. Repeat this operation several times.

[0060] Step 5: After multiple operations, saturation is completed, the experiment is stopped, the core holder 5 is opened, the core is taken out, G2 is weighed, and the volume of experimental oil in the collection container 7 is read.

[0061] Step 6: Calculate the saturated oil volume ΔG=G2-G1.

[0062] The experimental results of 1# core before and after applying the existing core saturation oil method are shown in Table 1:

[0063] Table 1

[0064]

[0065] Example: 2# Unconventional Ultra-low Permeability Shale Core

[0066] In this embodiment of the core saturation oil method, the pulse generator 1 uses a single-cylinder plunger pump, and the injection speed of the single-cylinder plunger pump is set to 0.01 ml / min throughout the whole process. The specific operation steps and experimental results are as follows:

[0067] Step 1: Start the annular pressure pump 10, apply annular pressure to the core holder 5 through the annular pressure tank 8 until the annular pressure gauge 9 displays 3.0 MPa, open the core inlet valve 4, start the single-cylinder plunger pump 1, inject the experimental oil in the oil sample container tank 2 at a low speed, increase the pressure until the inlet pressure gauge 3 displays the core inlet pressure of 1.0 MPa, then open the core outlet valve 6, and collect the experimental oil through the collection container 7 at the core outlet end. When the pressure of the inlet pressure gauge 3 drops to 0.5 MPa, continue to start the single-cylinder plunger pump 1, use pulse injection to increase the pressure to the inlet pressure gauge 3 to the set pressure of 1.0 MPa, and repeat the pressure reduction / pressure increase operation 5 times.

[0068] Step 2: Continue to increase the annular pressure of the core holder 5 to 5.0 MPa, start the single-cylinder plunger pump 1 to increase the pressure to 3.0 MPa on the core inlet pressure gauge 3. When the pressure on the inlet pressure gauge 3 drops to 2.0 MPa, continue to start the single-cylinder plunger pump 1, and use pulse injection to increase the pressure to the inlet pressure gauge 3 to the set pressure of 3.0 MPa. Repeat the pressure reduction / increase operation 5 times.

[0069] Step 3: Continue to increase the annular pressure of the core holder 5 to 7.0MPa, start the single-cylinder plunger pump 1 to increase the pressure to 5.0MPa on the core inlet pressure gauge 3. When the pressure on the inlet pressure gauge 3 drops to 4.0MPa, continue to start the single-cylinder plunger pump 1, and use pulse injection to increase the pressure to the inlet pressure gauge 3 to the set pressure of 5.0MPa. Repeat the pressure reduction / increase operation 5 times.

[0070] Step 4: Continue to increase the annular pressure of the core holder 5 to 9.0 MPa, start the single-cylinder plunger pump 1 to increase the pressure to 7.0 MPa on the core inlet pressure gauge 3. When the pressure of the inlet pressure gauge 3 drops to 6.0 MPa, continue to start the single-cylinder plunger pump 1, and use pulse injection to increase the pressure to the inlet pressure gauge 3 to the set pressure of 7.0 MPa. Repeat the pressure reduction / increase operation 5 times.

[0071] Step 5: Continue to increase the annular pressure of the core holder 5 to 11.0 MPa, start the single-cylinder plunger pump 1 to increase the pressure to 9.0 MPa on the core inlet pressure gauge 3. When the pressure of the inlet pressure gauge 3 drops to 8.0 MPa, continue to start the single-cylinder plunger pump 1, and use pulse injection to increase the pressure to the inlet pressure gauge 3 to the set pressure of 9.0 MPa, and repeat the pressure reduction / increase operation 5 times.

[0072] Step 6: Continue to increase the annular pressure of the core holder 5 to 13.0 MPa, start the single-cylinder plunger pump 1 to increase the pressure to 11.0 MPa on the core inlet pressure gauge 3. When the pressure of the inlet pressure gauge 3 drops to 10.0 MPa, continue to start the single-cylinder plunger pump 1, and use pulse injection to increase the pressure to the inlet pressure gauge 3 to the set pressure of 11.0 MPa. Repeat the pressure reduction / increase operation 5 times and stop the experiment.

[0073] Step 7: After saturation is completed, open the core holder 5, take out the core, weigh G2, and read the volume of experimental oil in the collection container 7.

[0074] Step 8: Calculate the saturated oil volume ΔG=G2-G1.

[0075] The experimental results of the 2# core before and after the core saturation oil method of the present invention is applied are shown in Table 2:

[0076] Table 2

[0077]

[0078] It can be seen from the data of 1# and 2# unconventional ultra-low permeability shale cores that the saturated oil content of the cores by the existing method is 0.2181g, and the saturated oil content by the technical method provided by the present invention is 1.1232g. The saturated oil content by the method of the present invention is increased by 0.9051g. Moreover, after the experiment, it was found that no experimental oil was found at the outlet of 1# core, while 19.8ml of experimental oil was collected at the outlet of 2# core, indicating that the experimental oil was blocked at the inlet end face of 1# core and did not completely pass through 1# core. Only a part of the experimental oil was saturated near the core inlet, indicating that the saturation was insufficient, and therefore the saturated oil content was very small.

[0079] It can be seen that the unconventional core saturation oil method provided by the present invention can solve the problem that unconventional ultra-low permeability shale cores are difficult to be saturated with oil, and can provide technical support for the development of unconventional oil reservoirs.

[0080] The above-mentioned embodiments are only embodiments of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person skilled in the art, without departing from the concept of the present invention, several variations, equivalent substitutions, improvements, etc. can be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the attached claims.

Claims

1. An unconventional core saturation oil method, characterized by: include: Step 1: obtaining the target reservoir formation pressure based on the target reservoir conditions; Step 2: Prepare for the saturated oil experiment; Step 3, injecting the experimental oil into the core at a low speed by pulse injection, and stopping the injection when the core inlet pressure rises to the initial pressure setting value; the low speed injection rate by pulse injection is 0.001-0.1 ml / min; Step 4, open the core outlet valve, when the core inlet pressure drops, continue to use pulse injection to increase the pressure to the first pressure setting value, maintain the steady pressure state for a certain period of time, and then increase the inlet pressure to the next pressure setting value, completing the process of injecting experimental oil into the core; Maintaining the stable pressure state for a certain period of time means that the pressure reduction and pressure increase operations in step 4 are repeated multiple times within a certain pressure setting value; Step 5, repeat steps 3 and 4 multiple times, with the pressure setting value for each repetition being the pressure setting value after the last inlet pressure increase plus the preset value, until the core inlet pressure is increased to the target reservoir formation pressure value, and saturation is completed.

2. The unconventional core saturation oil method according to claim 1, characterized in that: The pulse injection is achieved by a pulse generator; The pulse generator is a pulse injection pump or a single-cylinder plunger pump.

3. The unconventional core saturation oil method according to claim 1, characterized in that: Step 4: Open the core outlet valve and collect the experimental oil at the core outlet.

4. The unconventional core saturation oil method according to claim 1, characterized in that: When the drop in the core inlet pressure in step 4 reaches half of the sum of the previous pressure setting value and the current pressure setting value, pulse injection is continued to be used to increase the pressure to the current pressure setting value.

5. The unconventional core saturation oil method according to claim 1, characterized in that: The step 4 is repeated for 3 to 5 times.

6. The unconventional core saturation oil method according to claim 1, characterized in that: The first pressure setting value is gradually increased to a target reservoir formation pressure value.

7. The unconventional core saturation oil method according to claim 6, characterized in that: The pressure gradient from the initial pressure setting value to the target reservoir formation pressure value is 1-2MPa.

8. The unconventional core saturation oil method according to claim 1, characterized in that: The oil saturation experiment is realized by physically simulating a core oil saturation device in a laboratory.

9. The unconventional core saturation oil method according to claim 8, characterized in that: The laboratory physical simulation core saturated oil device comprises a core holder, the inlet pipeline of the core holder is connected to a pulse generator and an oil sample container tank, the pulse generator is a single-cylinder plunger pump or a pulse pump, the inlet pipeline of the core holder is connected to an inlet pressure gauge and a core inlet valve; the outlet pipeline of the core holder is connected to a core outlet valve and a collection container; the middle part of the core holder is connected to an annular pressure system, and the annular pressure system comprises an annular pressure tank, an annular pressure gauge, and an annular pressure pump; The experimental preparation process includes: Through the laboratory physical simulation of the core saturated oil device, the experimental oil is put into the oil sample container tank, and the pulse injection pump or single-cylinder plunger pump is set to inject the speed throughout the process; Turn on the oven heating system and raise the temperature to the target reservoir temperature. Select a natural core and weigh the core dry weight G1. Then put the core into the holder, use the ring pressure pump to increase the ring pressure until the ring pressure gauge shows the set value, and evacuate the core.

10. Use of the unconventional core saturated oil method according to any one of claims 1 to 9 in evaluating unconventional ultra-low permeability shale core saturated oil.

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