Oil washing method for full-diameter long cores

Abstract

The present invention relates to a method for washing oil in a full-diameter long core, which comprises: placing the core in a constant temperature box to allow soluble matter in the core to flow, then re-placing the full-diameter long core in a full-diameter core holder, establishing an oil washing process, using a reciprocating displacement method of an oil washing agent to remove impurities and crude oil contained in the core, performing multiple rounds of oil washing with the oil washing agent, setting one round of oil driving as 6 cycles, and sampling the oil washing agent in an intermediate container after each round until the oil washing meets the qualified standard. The oil washing method of the present invention is simple and convenient, can greatly improve the oil washing efficiency, is convenient for oil washing, has good sealing performance, and uses an inexpensive and easily available oil washing agent, thereby reducing the cost of oil washing.

Description

Technical Field

[0001] The invention belongs to a safe and efficient oil washing method for natural full-diameter cores or artificial cores in the field of core analysis in the petroleum industry, and particularly relates to an oil washing method for full-diameter long cores. Background Art

[0002] In oilfield exploration and development planning, laboratory core experiments can analyze the production patterns of specific development blocks and provide important guidance for the formulation of development plans. Before developing an oilfield block, full-diameter core samples must be obtained through drilling and coring techniques. Laboratory core experiments are then conducted to obtain in-situ experimental data, such as permeability and porosity, from the cores within the development formations, allowing for analysis of the core's physical and chemical properties. Therefore, core washing is a crucial step in some oilfield exploration and development experiments. Its purpose is to clean and remove crude oil and impurities from the cores, ensuring the smooth progress of subsequent experiments. Currently, there are two main methods for oil washing: the first involves the unidirectional displacement of polymers, surfactants, toluene, and other agents into a core holder. However, this unidirectional method is inefficient, and oil washing agents are expensive and difficult to obtain. Furthermore, toluene itself is toxic and volatile, requiring sealed laboratory procedures to avoid potential health hazards to laboratory personnel. The second method uses centrifugal force to apply kinetic energy to remove impurities from the core. This method has certain power advantages, but it is greatly affected by the core permeability and has a relatively low cleaning efficiency. Neither method can be used to remove cores with a full diameter of 80 cm in length and 10 cm in diameter. Summary of the Invention

[0003] The purpose of the present invention is to provide a full-diameter long core oil washing method. This full-diameter long core oil washing method is used to solve the problem that the existing technology cannot perform full-diameter long core oil washing with a length of 80 cm and a diameter of 10 cm, and the oil washing efficiency is slow and the oil washing effect is poor.

[0004] The technical solution adopted by the present invention to solve the technical problem is: this full-diameter long core oil washing method includes the following steps:

[0005] (1) Use drilling coring technology to obtain a full-diameter long core. The core is a columnar natural core with a length of 80-85 cm and a diameter of 10 cm. Measure the core diameter, length, and dry weight A to obtain core basic data;

[0006] (2) Place the full-diameter core in a thermostatic box and set the heating temperature to 104°C for 12 hours to make the soluble matter in the core flowable;

[0007] (3) Place the full-diameter long core in a full-diameter core holder and connect it to a permeability tester to perform gas permeability testing under the conditions of a confining pressure of 2 MPa, room temperature, and no heat shrinkage;

[0008] (4) Put the full-diameter core and plunger into the heat shrink tubing, heat and wrap them tightly with the heat shrink tubing, and weigh the dry weight B together with the plunger after heat shrinkage;

[0009] (5) placing the full-diameter long core in a core holder, connecting it to a high-efficiency vacuum pump through a high-pressure pipeline under a confining pressure of 2 MPa and room temperature, and saturating the core with oil by self-priming for 12 hours;

[0010] (6) After full saturation, remove the full-diameter core and weigh the wet weight B together with the plunger to calculate the initial porosity;

[0011] (7) The full-diameter long core is placed back into the full-diameter core holder, and an oil washing process is established. The impurities and crude oil contained in the core are removed by using a reciprocating displacement method of the oil washing agent. Multiple rounds of oil washing are performed using the oil washing agent. One round of oil washing is set to 6 cycles. After each round, the oil washing agent in the piston container is sampled;

[0012] (8) Compare the colors of the oil washing agent samples taken from the piston container in each round until the oil washing is completed; after the oil washing process is completed, remove the heat shrink tubing wrapped around the core surface and the plungers at both ends of the full-diameter core holder to weigh the wet weight C, and finally place the core that has completed the oil washing process outdoors for 12 hours;

[0013] (9) The core was then placed in a thermostat, and the heating temperature was set to 102°C-104°C for 24 hours. The dry weight C was weighed and combined with the wet weight C to calculate the porosity after oil washing. Finally, the dried core was placed in a core holder, with a confining pressure of 2 MPa and no heating, and the permeability was measured by gas measurement.

[0014] The heat shrink sleeve in step (5) of the above scheme is a polytetrafluoroethylene heat shrink sleeve.

[0015] The oil washing agent in step (7) of the above scheme is No. 120 gasoline.

[0016] The oil washing process in step (7) of the above scheme is carried out in a reciprocating circulation displacement mechanism, which includes a full-diameter core holder, a first piston container, a second piston container, a first four-way valve, a second four-way valve, a displacement power source and a confining pressure power source. A heating and temperature control system is provided on the full-diameter core holder, and the heating and temperature control system is equipped with a nano-heating coil and a temperature sensor for measuring the temperature of the full-diameter core holder. The full-diameter core holder is provided on a fixed frame; the confining pressure power source is composed of a high-pressure pump connected to the full-diameter core holder through a high-pressure pipeline to provide radial pressure to the core; The two ends of the full-diameter core holder are connected to the first piston container and the second piston container respectively through high-pressure pipelines. The first piston container is filled with oil washing agent. The lower end of the first piston container is connected to the first four-way valve, and the lower end of the piston of the second piston container is connected to the second four-way valve. The displacement power source is composed of the first four-way valve and the second four-way valve, both of which are connected to the high-pressure gas cylinder through high-pressure pipelines. The first piston container, the first four-way valve, the full-diameter core holder, the second piston container, the second four-way valve, and the displacement power source constitute a reciprocating circulation loop, and the valves arranged on each high-pressure pipeline in the loop are equipped with pressure sensors.

[0017] In the above scheme, the full-diameter core holder is heated to 50-60° C. by a heating temperature control system.

[0018] In the above solution, a pressure sensor is installed at the outlet end of the full-diameter core holder, and the pressure sensor is installed on the high-pressure pipeline connected to the outlet end of the core.

[0019] In the above solution, one valve port of the first four-way valve is connected to the first beaker; and one valve port of the second four-way valve is connected to the second beaker.

[0020] The full-diameter long core oil washing method of the present invention has the following beneficial effects:

[0021] 1. The oil washing agent of the present invention uses No. 120 gasoline, which is inexpensive and easily available. It is not easy to cause melting catalysis of the rubber sleeve in the full-diameter core holder, thereby extending the service life of the experimental sealing rubber sleeve. In addition, this oil washing agent is not easy to react with the crude oil in the core, thereby reducing the change of the original properties of the core, providing an accurate basis for subsequent indoor experiments.

[0022] 2. This invention uses heat-shrink tubing to shrink-wrap the core, preventing contact between the oil-washing agent and the sealing rubber sleeve. This also reduces contact between the experimenter and the washed core, which is beneficial to the health of the experimenter. The heat-shrink sleeve wrapped around the core surface increases the contact area between the core and the sealing rubber sleeve, ensuring an airtight seal throughout the experiment and maximizing the oil-washing effect.

[0023] 3. The full-diameter core holder used in the oil washing process of the present invention overcomes the problem of small core size for oil washing. At the same time, the core holder can wash oil at multiple angles, such as vertically, which can greatly accelerate the oil washing efficiency.

[0024] 4. The core oil washing method of the present invention is simple, easy to operate, and has good sealing performance. Through the reciprocating cycle of oil washing, crude oil and soluble matter in the core can be effectively removed, the oil washing time can be shortened to the greatest extent, and good oil washing effect can be achieved.

[0025] 5. This invention utilizes a reciprocating cyclic displacement method to wash oil from cores, overcoming the problem of smaller core wash sizes in existing systems. The experimental process is simple and convenient, effectively improving oil washing efficiency. Furthermore, the oil wash agent is inexpensive and readily available. By wrapping the full-diameter core with heat shrink tubing, the contact between the experimenter and the oil wash agent is significantly reduced, minimizing health risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the oil washing process structure of the full-diameter long core oil washing method;

[0027] Figure 2 This is a schematic diagram of the vacuum saturation process structure of the full-diameter long core oil washing method.

[0028] Numbers in the figure: 1-high-pressure gas cylinder; 2-full-diameter core holder; 3-high-pressure pump; 4-first piston container; 5-second piston container; 6-heating and temperature control system; 7-pressure sensor; 8-first four-way valve; 9-second four-way valve; 81-first displacement valve; 91-second displacement valve; 82-first signal valve, 92-second signal valve; 10-first beaker, 11-second beaker; 12-high-efficiency vacuum pump. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the embodiments described in the accompanying drawings, but the present invention is not limited to the scope of the embodiments, which is only indicated by the scope of the claims.

[0030] The novel method for washing oil from a full-diameter long core of the present invention will be described below with reference to specific embodiments.

[0031] Combine Figure 1-2 As shown, the novel method for washing oil from a full-diameter long core of the present invention comprises the following steps:

[0032] (1) Drilling and coring is used to obtain natural full-diameter cylindrical cores of the size required for the experiment. The clamping size of the full-diameter core holder 2 for indoor experiments can be matched to obtain a natural long core with a diameter of 10 cm and a length of 65 to 85 cm.

[0033] (2) placing the full-diameter long core obtained in step (1) in a thermostatic chamber, setting the heating temperature to 104°C and the heating time to 12 hours, even if the crude oil and soluble matter in the core are in a flowable state;

[0034] (3) placing the full-diameter long core in step (1) in a full-diameter core holder 2, and performing gas permeability measurement under the conditions of a confining pressure of 2 MPa, room temperature, and no thermal shrinkage;

[0035] (4) Place the plungers at both ends of the full-diameter long core in step (1), heat and wrap them tightly with a heat shrink sleeve, and weigh the dry weight B together with the plunger after heat shrinkage;

[0036] (5) The full-diameter long core in step (1) is placed in a full-diameter core holder 2, and connected to a high-efficiency vacuum pump 12 through a high-pressure pipeline under the conditions of a confining pressure of 2 MPa and room temperature, so that the core is in a negative pressure vacuum state, and then the core is saturated with oil by self-priming, and the saturation time is 12 hours;

[0037] (6) After the core is fully saturated, take out the core from the full-diameter core holder 2 in step (5) and weigh the wet weight B together with the plunger to calculate the initial porosity;

[0038] (7)Reference Figure 1As shown, the full-diameter long core in step (6) is installed in the full-diameter core holder. The full-diameter core holder 2 has a diameter of 40 cm and a length of 120 cm. Its structure includes a heat shrinkable rubber sleeve that wraps the core in the holder, a holder body, and plungers at both ends of the inlet and outlet. The core holder is mounted on a fixed frame that can rotate radially. Water is injected into the inner space of the full-diameter core holder by a high-pressure pump 3 to form a confining pressure. Then, pressure can be applied to tightly wrap the core with the heat shrinkable rubber sleeve. At the same time, the heat shrinkable sleeve wrapped around the core surface can prevent the oil wash agent from contacting the sealing rubber sleeve, so that the oil wash agent can only flow through the core in the full-diameter core holder from the inlet end. A pressure sensor 7 is installed at the outlet end of the full-diameter core holder. The pressure sensor 7 is installed on the high-pressure pipeline connected to the outlet end of the core. The heating and temperature control system 6 is started, and the temperature is set at 50°C and kept constant. At the same time, the first piston container 4 set at the left end of the full-diameter core holder 2 is filled with oil wash agent. Open the first displacement valve 81 and the second signal valve 92, and close the first signal valve 82 and the second displacement valve 91. Open the high-pressure gas cylinder 1 for displacement, and the oil washing agent flows through the core in the full-diameter core clamp and flows into the second piston container 5. At this time, bubbles are generated in the second beaker 11. After the bubbles disappear completely, close the first displacement valve 81 and the second signal valve 92, and open the first signal valve 82 and the second displacement valve 91. The oil washing agent flows from the second piston container 5 through the core and then flows back to the first piston container 4. At this time, bubbles are generated in the first beaker 10. After the bubbles disappear completely, one cycle is completed. Repeat this operation to perform a reciprocating displacement method to remove impurities and crude oil contained in the core. Set one round of oil drive to 6 cycles, and sample the oil washing agent after each round;

[0039] (8) According to step (7), the oil washing agent in each round of the first piston container 4 is sampled and the color is comprehensively compared until the oil washing is determined to be completed; after the oil washing process is completed, the heat shrink sleeve wrapped around the core surface and the plungers at both ends of the full-diameter core holder are removed to weigh the wet weight C, and finally the core after the oil washing process is completed is placed outdoors and left to stand for 12 hours;

[0040] (9) The core is then placed in a constant temperature box at 104°C for 24 hours; the dry weight C is weighed and combined with the wet weight C to calculate the porosity after oil washing; finally, the dried core is placed in a core holder 2 at a confining pressure of 2 MPa without heating, and the permeability is measured by gas measurement.

[0041] The present invention places a first piston container 4 and a second piston container 5 at both ends of the full-diameter core clamp 2. The first piston container 4 is filled with an oil washing agent, and a channel for the oil washing agent is established in the core to form a reciprocating oil washing mode, which greatly improves work efficiency. Example 1:

[0042] To conduct laboratory porosity and permeability tests before and after oil washing on a full-diameter long core from a development block in an oilfield, the core must be subjected to oil washing. The full-diameter long core was sandstone, with a diameter of 10 cm, a length of 82 cm, and a dry weight of 2348 g. The oil was washed using the oil washing method described above.

[0043] Place 120# gasoline in the left piston container, place the dried full-diameter core in the full-diameter core holder, and measure the permeability under the conditions of no heat shrinkage, constant temperature, and confining pressure of 2MPa; after heat shrinkage, weigh the dry weight B together with the plunger, and then vacuum-saturate the full-diameter core with oil; after sufficient saturation, take out the core, weigh the wet weight B together with the plunger, and calculate the initial porosity; by re-placing the full-diameter core in the core holder, confining pressure 2MPa, temperature 50℃, and oil washing agent 4L, complete the reciprocating oil washing channel, and then perform multiple rounds of washing. The oil flow process is set to 6 cycles per round of oil flooding, and the washed oil is sampled after each round. 6 to 8 rounds of oil washing are expected. Based on the color of the oil washing agent samples, comprehensive comparison and photography are taken to determine the end of oil washing. The cores after oil washing are taken out, and the heat shrink sleeve and plunger are removed to weigh the wet weight C. The washed cores are placed outdoors for 12 hours. The cores are then placed in a constant temperature box at 104°C for 24 hours. The dry weight C is weighed and combined with the wet weight C to calculate the porosity after oil washing. The dried cores are placed in a core holder at a confining pressure of 2MPa and gas permeability is measured without heating.

[0044] The full-diameter core underwent six rounds of oil washing. The permeabilities before and after oil washing were 495.01 mD and 623.81 mD, and the porosities were 14.95% and 18.84%, respectively. This demonstrates that the present invention effectively removes crude oil and soluble substances from the core. A comprehensive comparison of sampling images shows that the color of the first round of oil washing is brown, and the color depth gradually decreases with each washing round, reaching an overall yellow color. There is no significant color change between the second and third rounds, and the color changes from brown to light yellow in the final round, demonstrating a good oil washing effect. Furthermore, the entire process takes only three days, greatly improving oil washing efficiency.

[0045] The present invention uses a drilling coring technique to obtain a long-diameter rock sample; after placing the core in a constant temperature chamber to allow the soluble matter in the core to flow, the full-diameter long core is then placed back into a full-diameter core holder, and an oil washing process is established. A reciprocating displacement method of an oil washing agent is used to remove impurities and crude oil contained in the core. Multiple rounds of oil washing are performed using the oil washing agent, with one round of oil driving being set to six cycles. After each round, the oil washing agent in the intermediate container is sampled until the oil washing meets the qualified standard; the core is then placed in a constant temperature chamber. The oil washing method of the present invention is simple and convenient, and can greatly improve the oil washing efficiency. The oil washing device has a simple structure, is convenient for oil washing, has good sealing properties, and the oil washing agent used is inexpensive and easily available. The full-diameter core holder used in the oil washing process solves the problem that the prior art only allows oil washing of smaller cores. At the same time, the core holder can perform oil washing at multiple angles, which can greatly improve the oil washing efficiency.

Claims

1. A full diameter long core oil washing method, characterized in that The steps include: (1) Use drilling coring technology to obtain a full-diameter long core. The core is a columnar natural core with a length of 80-85 cm and a diameter of 10 cm. Measure the core diameter, length, and dry weight A to obtain core basic data; (2) Place the full-diameter core in a thermostatic box and set the heating temperature to 104°C for 12 hours to make the soluble matter in the core flowable; (3) Place the full-diameter long core in a full-diameter core holder and connect it to a permeability tester to perform gas permeability testing under the conditions of a confining pressure of 2 MPa, room temperature, and no heat shrinkage; (4) Put the full-diameter core and plunger into the heat shrink tubing, heat and wrap them tightly with the heat shrink tubing, and weigh the dry weight B together with the plunger after heat shrinkage; (5) placing the full-diameter long core in a core holder, connecting it to a high-efficiency vacuum pump through a high-pressure pipeline under a confining pressure of 2 MPa and room temperature, and saturating the core with oil by self-priming for 12 hours; (6) After full saturation, remove the full-diameter core and weigh the wet weight B together with the plunger to calculate the initial porosity; (7) The full-diameter long core is placed back into the full-diameter core holder, and an oil washing process is established. The impurities and crude oil contained in the core are removed by using a reciprocating displacement method of the oil washing agent. Multiple rounds of oil washing are performed using the oil washing agent. One round of oil washing is set to 6 cycles. After each round, the oil washing agent in the piston container is sampled; (8) Compare the colors of the oil washing agent samples taken from the piston container in each round until the oil washing is completed; after the oil washing process is completed, remove the heat shrink tubing wrapped around the core surface and the plungers at both ends of the full-diameter core holder to weigh the wet weight C, and finally place the core that has completed the oil washing process outdoors for 12 hours; (9) The core was then placed in a thermostat, and the heating temperature was set to 102°C-104°C for 24 hours. The dry weight C was weighed and combined with the wet weight C to calculate the porosity after oil washing. Finally, the dried core was placed in a core holder, with a confining pressure of 2 MPa and no heating, and the permeability was measured by gas measurement.

2. The full-diameter long core oil washing method according to claim 1, characterized in that: The heat shrinkable sleeve in step (5) is a polytetrafluoroethylene heat shrinkable sleeve.

3. The full-diameter long core oil washing method according to claim 2, characterized in that: The oil washing agent in step (7) is No. 120 gasoline.

4. The full-diameter long core oil washing method according to claim 3, characterized in that: The oil washing process in step (7) is carried out in a reciprocating circulation displacement mechanism, which includes a full-diameter core holder, a first piston container, a second piston container, a first four-way valve, a second four-way valve, a displacement power source and a confining pressure power source. A heating and temperature control system is provided on the full-diameter core holder, and the heating and temperature control system is provided with a nano-heating coil and a temperature sensor for measuring the full-diameter core holder. The full-diameter core holder is provided on a fixed frame; the confining pressure power source is composed of a high-pressure pump connected to the full-diameter core holder through a high-pressure pipeline to provide radial pressure to the core; the full-diameter core holder is provided with a high-pressure pump connected to the full-diameter core holder through a high-pressure pipeline to provide radial pressure to the core; the full-diameter core holder is provided with a high-pressure pump connected to the full-diameter core holder through a high-pressure pipeline to provide radial pressure to the core; the full-diameter core holder is provided with a heating and temperature control system. The two ends of the full-diameter core clamp are respectively connected to the first piston container and the second piston container through high-pressure pipelines. The first piston container is filled with oil washing agent. The lower end of the first piston container is connected to the first four-way valve, and the lower end of the piston of the second piston container is connected to the second four-way valve; the displacement power source is composed of the first four-way valve and the second four-way valve, both of which are connected to the high-pressure gas cylinder through high-pressure pipelines; the first piston container, the first four-way valve, the full-diameter core clamp, the second piston container, the second four-way valve, and the displacement power source constitute a reciprocating circulation loop, and the valves arranged on each high-pressure pipeline in the loop are equipped with pressure sensors.

5. The full-diameter long core oil washing method according to claim 4, characterized in that: The full-diameter core holder is heated to 50-60° C. by a heating temperature control system.

6. The full-diameter long core oil washing method according to claim 5, characterized in that: A pressure sensor is installed at the outlet end of the full-diameter core holder, and the pressure sensor is installed on a high-pressure pipeline connected to the outlet end of the core.

7. The full-diameter long core oil washing method according to claim 6, characterized in that: One valve port of the first four-way valve is connected to the first beaker; and one valve port of the second four-way valve is connected to the second beaker.

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