A method for evaluating performance of a multi-stage plug

Abstract

This invention discloses a method for evaluating the performance of multi-stage plugging agents. Through core displacement experiments, artificial cores saturated with formation water are displaced using plugging agents. Nuclear magnetic resonance (NMR) testing is then used to test the distribution of the plugging agent after saturation and expansion within the core at different injection pressures, evaluating the distribution patterns of different plugging agents in the core matrix or fractures. First, an artificial core containing artificial fractures is fabricated, with the fractures not penetrating the core. The core is then saturated with simulated formation water. Second, during the core displacement experiment, a confining pressure of 15–20 MPa is set, and continuous displacement experiments with the plugging agent are conducted until the artificial core is completely saturated. The experiment is then repeated with a new constant inlet pressure. Finally, after the plugging agent has fully expanded, NMR T2 spectra are obtained from the core to acquire the core T2 spectrum curves of the plugging agent under different injection pressures. This evaluates the different distribution patterns of the plugging agent in the core matrix and fractures, guiding the field application of plugging agents.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field production and development technology, and specifically relates to a method for evaluating the performance of multi-segment plugging agents. Background Technology

[0002] After years of water injection development, many blocks in Changqing Oilfield have entered a "high water cut and high water level" development stage. Rising water cut has led to a rapid decline in oil well production. Across the oilfield, 7,358 wells have been shut down due to high water cut and water flooding, impacting annual production capacity by 2 million tons and severely affecting the oilfield's sustainable, efficient, and stable production. To restore production capacity from water-bearing wells and improve reservoir development, water well regulation and water shut-off measures have been implemented. The effectiveness of these measures is affected by factors such as the performance, distribution, and dosage of the plugging agent. Therefore, a suitable experimental method for evaluating the performance of plugging agents is fundamental to ensuring the effectiveness of water well regulation and water shut-off measures. Previous experimental methods for evaluating plugging agent performance mainly assessed the viscosity and strength of the plugging agent system. This evaluation method primarily assesses the distribution patterns of different plugging agents in the matrix and fractures. Summary of the Invention

[0003] A method for evaluating the performance of multi-stage plugging agents involves using core displacement experiments to displace artificial cores saturated with formation water with plugging agents. Nuclear magnetic resonance (NMR) testing is then used to test the distribution of the plugging agents after saturation and expansion within the core at different injection pressures, thereby evaluating the distribution patterns of different plugging agents in the core matrix or fractures.

[0004] The technical solution adopted in this invention is: a method for evaluating the performance of multi-segment plugging agents, the specific operation steps of which are as follows:

[0005] Step 1: Use wire cutting to create artificial cracks in the artificial rock core to produce a rock core that meets experimental specifications;

[0006] Step 2: Place the core prepared in Step 1 in a drying oven to dry it. Then place the dried core in a core saturation device and use formation water as a medium to saturate it for more than 72 hours at room temperature to obtain a saturated formation water artificial core.

[0007] Step 3: Conduct nuclear magnetic resonance T2 spectrum testing on the artificial rock core with saturated formation water from Step 2 to obtain the T2 spectrum curve of the rock core under saturated water conditions;

[0008] Step 4: After testing the T2 NMR spectrum of the artificial core saturated with formation water, place the core in the core holder, set the confining pressure, and inject a plugging agent to displace the core. Different injection pressures are set when injecting the plugging agent, the injection pressure is 1-15 MPa. When the liquid discharged from the outlet of the core holder reaches 2-3 PV, where PV refers to the pore volume, it is considered that the plugging agent is completely saturated with the artificial core.

[0009] Step 5: Place the saturated artificial core after displacement in Step 4 in a water bath at 60-70℃ and maintain this temperature for more than 7 days to ensure that the plugging agent fully expands in the artificial core; conduct nuclear magnetic resonance T2 spectrum tests on the core after the plugging agent has expanded to obtain the core T2 spectrum curve under the plugging agent injection condition, thereby obtaining the dynamic plugging effect of the plugging agent under different pressures.

[0010] Step 6: Repeat steps 4-5 using different plugging agents, and then compare the different patterns of the plugging agents in the core sample to select the best plugging agent for field application.

[0011] The invention is further characterized in that,

[0012] Step 1: The artificial rock core is made into a cylindrical shape with a diameter of 25mm and a length of 50mm.

[0013] Step 2, drying, involves drying at 80–85℃ for 48–50 hours.

[0014] In step 1, artificial cracks are made along the length of the artificial rock core, and the cracks do not penetrate both ends of the artificial rock core.

[0015] In step 4, different injection pressures are set according to the actual reservoir pressure under the condition that no new fractures are opened.

[0016] When injecting the sealing agent in step 4, set the confining pressure to 15-20 MPa.

[0017] In step 5, the actual reservoir temperature in the mine is used as the basis for determining the temperature and maintaining it for more than 7 days, based on the time required for the plugging agent to completely solidify.

[0018] Step 4: The core holder is manufactured by Nantong Huaxing Petroleum Instrument Co., Ltd., model number φ25*80.

[0019] The beneficial effects of this invention are: it can test the distribution pattern of different plugging agents in artificial rock cores containing artificial fractures, and can accurately test the distribution of plugging agents in rock matrix and fractures. The results are accurate and highly referential, and have great guiding significance for the selection of plugging agent types for on-site water well profile control and oil well water shut-off.

[0020] Scope of application and prospects of this invention: This invention belongs to the field of reservoir enhancement measures in oil production engineering. It provides a method for evaluating the performance of multi-stage plugging agents. In the field of water injection oilfields, where competition is fierce and market demand is large, this innovative achievement is one of the effective and essential technical methods to be used after a certain period of development in any water injection oilfield. Detailed Implementation

[0021] The present invention provides a method for evaluating the performance of multi-segment plugging agents, which is implemented according to the following steps:

[0022] Step 1: Use wire cutting to artificially create cracks in the artificial rock core to make a rock core that meets the experimental specifications. The artificial rock core is made into a cylindrical shape with a diameter of 25mm and a length of 50mm. The artificial cracks are made along the length of the inside of the rock core and do not penetrate into the two ends of the artificial rock core.

[0023] Step 2: Place the core prepared in Step 1 in a drying oven and dry it at 80-85℃ for 48-50 hours. Then place the dried core in a core saturation device and saturate it with formation water as the medium at room temperature for more than 72 hours to obtain a saturated formation water artificial core.

[0024] Step 3: Conduct nuclear magnetic resonance T2 spectrum testing on the artificial rock core with saturated formation water from Step 2 to obtain the T2 spectrum curve of the rock core under saturated water conditions;

[0025] Step 4: After testing the T2 NMR spectrum of the artificial core saturated with formation water, place the core in a core holder and set the confining pressure to 15-20 MPa. Inject a plugging agent to displace the core. Different injection pressures are set when injecting the plugging agent, with the injection pressure being 1-15 MPa. When the liquid discharged from the outlet of the core holder reaches 2-3 PV, where PV refers to the pore volume, it is considered that the plugging agent has completely saturated the artificial core.

[0026] Step 5: Place the saturated artificial core after displacement in Step 4 in a water bath at 60-70℃ and maintain this temperature for more than 7 days to ensure that the plugging agent fully expands in the artificial core; conduct nuclear magnetic resonance T2 spectrum tests on the core after the plugging agent has expanded to obtain the core T2 spectrum curve under the plugging agent injection condition, thereby obtaining the dynamic plugging effect of the plugging agent under different pressures.

[0027] Step 6: Repeat steps 4-5 using different plugging agents, and then compare the different patterns of the plugging agents in the core sample to select the best plugging agent for field application.

[0028] In step 5, the core is placed in a water bath at 60-70°C, depending on the actual reservoir temperature at the mine; and this temperature is maintained for more than 7 days, depending on the time it takes for the plugging agent to completely solidify.

[0029] Example 1:

[0030] A method for evaluating the performance of multi-stage plugging agents is proposed. This method involves core displacement experiments, where the plugging agent displaces an artificial core saturated with formation water. Nuclear magnetic resonance (NMR) testing is then used to assess the distribution of the plugging agent after saturation and expansion within the core at different injection pressures. The distribution patterns of different plugging agents in the core matrix or fractures are evaluated. The specific construction steps are as follows:

[0031] Step 1: Use wire cutting to prepare artificial rock cores that meet experimental specifications;

[0032] Step 2: Place the core prepared in Step 1 in a drying oven and dry it at 80°C for 48 hours. Then place the dried core in a core saturation device and saturate it with formation water as the medium at room temperature for 72 hours to obtain a saturated formation water artificial core.

[0033] Step 3: Conduct nuclear magnetic resonance T2 spectrum testing on the artificial rock core with saturated formation water from Step 2 to obtain the T2 spectrum curve of the rock core under saturated water conditions;

[0034] Step 4: After testing the T2 NMR spectrum of the saturated formation water artificial core, place it in the core holder, set the confining pressure, and inject plugging agent A to displace the core. Different injection pressures are set when injecting plugging agent A. The injection pressure is 1 MPa. When the liquid discharged from the outlet of the core holder reaches 2 PV, it is considered that the plugging agent A is completely saturated with artificial core.

[0035] Step 5: Place the artificial core after displacement in Step 4 in a 60℃ water bath and maintain this temperature for more than 7 days to ensure that the plugging agent A is fully expanded in the artificial core. After the plugging agent A is expanded, perform nuclear magnetic resonance T2 spectrum testing on the core. The test results show that when the injection pressure is less than 3MPa, the plugging agent A is distributed in the matrix pores and fractures of the artificial core. When the injection pressure is between 3 and 10MPa, the plugging agent A is mainly distributed in the matrix pores of the artificial core, and there is no distribution of plugging agent A in the fractures. When the injection pressure is greater than 10MPa, the plugging agent A is not distributed in the matrix pores and fractures of the artificial core and is completely driven out.

[0036] Example 2:

[0037] A method for evaluating the performance of multi-stage plugging agents is proposed. This method involves core displacement experiments, where the plugging agent displaces an artificial core saturated with formation water. Nuclear magnetic resonance (NMR) testing is then used to assess the distribution of the plugging agent after saturation and expansion within the core at different injection pressures. The distribution patterns of different plugging agents in the core matrix or fractures are evaluated. The specific construction steps are as follows:

[0038] Step 1: Use wire cutting to prepare artificial rock cores that meet experimental specifications;

[0039] Step 2: Place the core prepared in Step 1 in a drying oven and dry it at 85°C for 48 hours. Then place the dried core in a core saturation device and saturate it with formation water as the medium at room temperature for 75 hours to obtain a saturated formation water artificial core.

[0040] Step 3: Conduct nuclear magnetic resonance T2 spectrum testing on the artificial rock core with saturated formation water from Step 2 to obtain the T2 spectrum curve of the rock core under saturated water conditions;

[0041] Step 4: After testing the nuclear magnetic resonance T2 spectrum of the saturated formation water artificial core, place it in the core holder, set the confining pressure, and inject plugging agent B to displace the core. Different injection pressures are set when injecting plugging agent B. The injection pressure is 15 MPa. When the liquid discharged from the outlet of the core holder reaches 3 PV, it is considered that the plugging agent A is completely saturated with artificial core.

[0042] Step 5: Place the artificial core after displacement in Step 4 in a 70℃ water bath and maintain this temperature for 8 days to ensure that the plugging agent B is fully expanded in the artificial core. After the plugging agent B is expanded, perform nuclear magnetic resonance T2 spectrum testing on the core. The test results show that when the injection pressure is less than 5 MPa, the plugging agent B is distributed in the matrix pores and fractures of the artificial core. When the injection pressure is greater than 5 MPa, the plugging agent B is mainly distributed in the matrix pores of the artificial core, and there is no distribution of plugging agent B in the fractures, indicating that the plugging agent B has a good sealing effect on the core matrix.

[0043] Example 3:

[0044] A method for evaluating the performance of multi-stage plugging agents is proposed. This method involves core displacement experiments, where the plugging agent displaces an artificial core saturated with formation water. Nuclear magnetic resonance (NMR) testing is then used to assess the distribution of the plugging agent after saturation and expansion within the core at different injection pressures. The distribution patterns of different plugging agents in the core matrix or fractures are evaluated. The specific construction steps are as follows:

[0045] Step 1: Use wire cutting to prepare artificial rock cores that meet experimental specifications;

[0046] Step 2: Place the core prepared in Step 1 in a drying oven and dry it at 82°C for 50 hours. Then place the dried core in a core saturation device and saturate it with formation water as the medium at room temperature for 72 hours to obtain a saturated formation water artificial core.

[0047] Step 3: Conduct nuclear magnetic resonance T2 spectrum testing on the artificial rock core with saturated formation water from Step 2 to obtain the T2 spectrum curve of the rock core under saturated water conditions;

[0048] Step 4: After testing the nuclear magnetic resonance T2 spectrum of the saturated formation water artificial core, place it in the core holder, set the confining pressure, and inject the plugging agent C to displace the core. Different injection pressures are set when injecting the plugging agent C, and the injection pressure is 1-15 MPa. When the liquid discharged from the outlet end of the core holder reaches 2.5 PV, it is considered that the plugging agent A is completely saturated with artificial core.

[0049] Step 5: Place the artificial core after displacement in Step 4 in a 65℃ water bath and maintain this temperature for more than 7 days to ensure that the plugging agent C is fully expanded in the artificial core; conduct nuclear magnetic resonance T2 spectrum test on the core after the plugging agent C is expanded. The test results show that under different injection pressures, the plugging agent C is mainly distributed in the fractures of the artificial core, and there is no distribution of plugging agent C in the matrix pores, indicating that the plugging agent C has a good effect on sealing fractures.

[0050] Example 4:

[0051] A method for evaluating the performance of multi-stage plugging agents is proposed. This method involves core displacement experiments, where the plugging agent displaces an artificial core saturated with formation water. Nuclear magnetic resonance (NMR) testing is then used to assess the distribution of the plugging agent after saturation and expansion within the core at different injection pressures. The distribution patterns of different plugging agents in the core matrix or fractures are evaluated. The specific construction steps are as follows:

[0052] Step 1: Use wire cutting to prepare artificial rock cores that meet experimental specifications;

[0053] Step 2: Place the core prepared in Step 1 in a drying oven and dry it at 80°C for 49 hours. Then place the dried core in a core saturation device and saturate it with formation water as the medium at room temperature for 80 hours to obtain a saturated formation water artificial core.

[0054] Step 3: Conduct nuclear magnetic resonance T2 spectrum testing on the artificial rock core with saturated formation water from Step 2 to obtain the T2 spectrum curve of the rock core under saturated water conditions;

[0055] Step 4: After testing the T2 NMR spectrum of the saturated formation water artificial core, place it in the core holder, set the confining pressure, and inject the plugging agent D to displace the core. Different injection pressures are set when injecting the plugging agent D. When the liquid discharged from the outlet of the core holder reaches 3PV, it is considered that the plugging agent D is completely saturated with the artificial core.

[0056] Step 5: Place the artificial core after displacement in Step 4 in a 60℃ water bath and maintain this temperature for 7 days to ensure that the plugging agent D fully expands in the artificial core. After the plugging agent D expands, perform nuclear magnetic resonance T2 spectrum testing on the core. The test results show that when the injection pressure is 1-8 MPa, the plugging agent D is distributed in the matrix pores and fractures of the artificial core. When the injection pressure is greater than 8-15 MPa, the plugging agent D is mainly distributed in the matrix pores of the artificial core, and there is no distribution of plugging agent D in the fractures, indicating that the plugging agent D is suitable for sealing the matrix pores of the core.

[0057] The principle of this invention is:

[0058] Through core displacement experiments, artificial cores saturated with formation water were displaced using plugging agents. Nuclear magnetic resonance (NMR) testing was used to test the distribution of the plugging agents after saturation and expansion in the cores under different injection pressures, and to evaluate the distribution patterns of different plugging agents in the core matrix or fractures.

Claims

1. A method for evaluating the performance of a multi-segment plugging agent, characterized in that, The specific operating steps are as follows: Step 1: Use wire cutting to create artificial cracks in the artificial rock core to produce a rock core that meets experimental specifications; Step 2: Place the core prepared in Step 1 in a drying oven to dry it. Then place the dried core in a core saturation device and use formation water as a medium to saturate it for more than 72 hours at room temperature to obtain a saturated formation water artificial core. Step 3: Conduct nuclear magnetic resonance T2 spectrum testing on the artificial rock core with saturated formation water from Step 2 to obtain the T2 spectrum curve of the rock core under saturated water conditions; Step 4: After testing the T2 NMR spectrum of the artificial core saturated with formation water, place the core in the core holder, set the confining pressure, and inject a plugging agent to displace the core. Different injection pressures are set when injecting the plugging agent, the injection pressure is 1-15 MPa. When the liquid discharged from the outlet of the core holder reaches 2-3 PV, where PV refers to the pore volume, it is considered that the plugging agent is completely saturated with the artificial core. Step 5: Place the saturated artificial core after displacement in Step 4 in a water bath at 60-70℃ and maintain this temperature for more than 7 days to ensure that the plugging agent fully expands in the artificial core; conduct nuclear magnetic resonance T2 spectrum tests on the core after the plugging agent has expanded to obtain the core T2 spectrum curve under the plugging agent injection condition, thereby obtaining the dynamic plugging effect of the plugging agent under different pressures. Step 6: Repeat steps 4-5 using different plugging agents, and then compare the different patterns of the plugging agents in the core sample to select the best plugging agent for field application.

2. The method for evaluating the performance of a multi-segment plugging agent according to claim 1, characterized in that, The artificial rock core described in step 1 is made into a cylindrical shape with a diameter of 25mm and a length of 50mm.

3. The method for evaluating the performance of a multi-segment plugging agent according to claim 1, characterized in that, The drying process described in step 2 involves drying at 80–85°C for 48–50 hours.

4. The method for evaluating the performance of a multi-segment plugging agent according to claim 1, characterized in that, The artificial cracking described in step 1 involves creating artificial cracks along the length of the rock core, without the cracks penetrating both ends of the artificial rock core.

5. The method for evaluating the performance of a multi-segment plugging agent according to claim 1, characterized in that, In step 4, different injection pressures are set according to the actual reservoir pressure under the condition that no new fractures are opened.

6. The method for evaluating the performance of a multi-segment plugging agent according to claim 1, characterized in that, When injecting the sealing agent in step 4, set the confining pressure to 15-20 MPa.

7. The method for evaluating the performance of a multi-segment plugging agent according to claim 1, characterized in that, The core holder mentioned in step 4 is manufactured by Nantong Huaxing Petroleum Instrument Co., Ltd., and its model number is φ25*80.