Method for enhanced oil recovery by inter-fracture water injection in a volume of a tight reservoir

Abstract

The present application relates to the technical field of oil exploitation, and particularly relates to a method for improving recovery by water injection between fractures of a volume-fractured horizontal well in a tight oil reservoir, comprising the following steps: constructing a water injection physical model between fractures of a horizontal well; establishing a bound water process for the water injection physical model between fractures of the horizontal well; and establishing a water injection physical simulation method between fractures of a volume-fractured horizontal well in a tight oil reservoir. The present application establishes a water injection physical simulation method for supplementing energy between fractures of a volume-fractured horizontal well in a tight oil reservoir, and explores the pressure distribution characteristics and production characteristics in the water injection process between fractures, so as to improve the recovery of the tight oil reservoir.

Description

Technical Field

[0001] This invention relates to the field of petroleum extraction technology, and in particular to a method for enhancing oil recovery by injecting water into fractures in horizontal wells with volumetric fracturing in tight oil reservoirs. Background Technology

[0002] Global tight oil reserves are abundant with enormous development potential. Tight oil is characterized by low porosity and low permeability, resulting in extremely dense reservoirs with high initiation pressure gradients. Therefore, horizontal well volumetric fracturing technology is typically required for the development of such reservoirs. However, the depletion-driven development of tight oil reservoirs after horizontal well volumetric fracturing faces challenges such as rapid production decline, lack of effective energy replenishment methods, and difficulty in establishing an effective inter-well displacement system. Furthermore, due to the development of microfractures in tight oil reservoirs, water injection into horizontally fractured wells can easily trigger water channeling and other problems.

[0003] For tight oil reservoirs, after volumetric fracturing, water injection between fractures can replenish energy and recover crude oil that could not be utilized during depletion development. This approach can reduce the efficiency issues caused by reducing well spacing and fundamentally solve the problem of establishing an effective displacement system.

[0004] The development methods for inter-fracture energy replenishment can be mainly divided into two modes based on the number of wells implementing the measures: the first is intra-fracture injection and production within the same well; the second is inter-fracture injection and production between different wells. Currently, scholars have proposed the concept of inter-fracture energy replenishment in horizontal wells and have conducted preliminary research using numerical simulation technology. However, they have not yet established physical simulation methods in the laboratory, and have not thoroughly explored the seepage mechanism during the inter-fracture water injection energy replenishment process. There is an urgent need to carry out basic theoretical research on inter-fracture water injection seepage in horizontal wells with volumetric fracturing in tight oil reservoirs. Summary of the Invention

[0005] To address the shortcomings of existing methods, this invention establishes a physical simulation method for water injection to replenish energy in fractures of horizontal wells with volumetric fracturing in tight oil reservoirs. This method explores the pressure distribution and production characteristics during water injection in fractures, thereby improving the recovery rate of tight oil reservoirs.

[0006] The technical solution adopted in this invention is as follows: A method for enhancing oil recovery by injecting water into the fracture spaces of a horizontal well undergoing volumetric fracturing in a tight oil reservoir includes the following steps:

[0007] Step 1: Construct a physical model for water injection between fractures in a horizontal well;

[0008] Furthermore, specifically including:

[0009] Step 11: Select the outcrop core of the target block and process it into a flat core model;

[0010] Furthermore, the permeability of the outcrop core was 0.4mD±0.01mD, and it was processed into a 50×50×3cm flat core model.

[0011] Step 12: Cut injection fractures and production fractures in the middle on the flat core model; drill several holes in the area enclosed by the two injection fractures, the production fractures, the two wellbores, and the wellbore of the injection fractures and production fractures.

[0012] Step 13: Fill the cracks with a mixture of quartz sand and AB glue, and then cover them with marble glue.

[0013] Step 14: Install a pressure sensor at the opening;

[0014] Step 15: After letting the flat core model stand for 2 hours, move it into the sealing mold.

[0015] Step 2: Establish a physical model for water injection into fractured horizontal wells to illustrate the process of bound water.

[0016] Furthermore, specifically including:

[0017] Step 21: Test the connectivity and sealing of each opening;

[0018] Step 22: Perform a vacuum test on the flat core model;

[0019] Step 23: When the vacuum pressure reaches -0.0999MPa, connect the simulated formation water to the vacuum measurement point and turn off the vacuum pump; the saturation process should last no less than 36 hours, and the simulated formation water should be weighed and the mass of the water recorded at regular intervals.

[0020] Step 24: After the simulated formation water saturation reaches the target tight oil reservoir requirement, stop the experiment and record the saturation water volume;

[0021] Step 25: Remove the flat core model from the saturation device and install it into the high-temperature and high-pressure sealed chamber, and connect all pressure interfaces to the wiring ports of the high-temperature and high-pressure sealed chamber.

[0022] Step 26: Open the pressure interface valve at the junction of the first injection fracture and the second wellbore, close the other pressure connection valves, increase the displacement pump pressure to 1.0 MPa, introduce kerosene into the intermediate container to purge, and then allow the high-temperature and high-pressure sealed chamber to settle.

[0023] Step 27: After confirming that there is no leakage in the high-temperature and high-pressure sealed chamber, close the pressure interface valve at the junction of the first injection fracture and the second wellbore;

[0024] Step 28: Use a confining pressure pump to pressurize the internal pressure of the flat core model to 20.0 MPa, and open and close the injection port, extraction port and pressure measurement point of the flat core model in a planar cross pattern.

[0025] Step 3: Establish a physical simulation method for water injection between fractures in horizontal wells with volumetric fracturing in tight oil reservoirs;

[0026] Furthermore, specifically including:

[0027] Step 31: After establishing the bound water in the flat core model, open the valves at the two pressure measuring points at the intersection of the first and second injection fractures and the first wellbore, open the valves at the pressure measuring point at the intersection of the extraction fracture and the second wellbore, and close the valves at other pressure measuring points.

[0028] Step 32: Set the displacement pump displacement pressure to 6.89 MPa and the outlet pressure to 0 MPa; then, turn on the automatic data acquisition device to start metering the outlet liquid; and save the test data in time using the pressure measurement point test software.

[0029] Step 33: When the moisture content reaches 90%, turn off the injection pump pressure and close all pressure measuring valves.

[0030] Furthermore, a system for enhancing oil recovery through interfracture water injection in a horizontal well with volumetric fracturing in a tight oil reservoir includes: a memory for storing instructions executable by a processor; and a processor for executing the instructions to implement a method for enhancing oil recovery through interfracture water injection in a horizontal well with volumetric fracturing in a tight oil reservoir.

[0031] Furthermore, a computer-readable medium storing computer program code, which, when executed by a processor, implements a method for enhancing oil recovery by injecting water into fractured horizontal wells in tight oil reservoirs.

[0032] The beneficial effects of this invention are:

[0033] A physical simulation experiment was conducted on water injection between fractures in a volumetric fractured horizontal well to replenish energy in a low-permeability tight oil reservoir. By measuring the pressure change characteristics and fluid output in the main areas of a flat core model during water injection between fractures, the seepage law of water injection between fractures in the volumetric fractured horizontal well can be obtained based on the tested pressure distribution characteristics, water output, and oil output. This can achieve the effect of improving oil recovery and provide a reference for analyzing and clarifying the applicability of water injection between fractures in this type of reservoir. Attached Figure Description

[0034] Figure 1 This is a flowchart of the method for enhancing oil recovery by injecting water into the fractures of a horizontal well with volumetric fracturing in a tight oil reservoir, according to the present invention.

[0035] Figure 2 This is a schematic diagram of the physical model of water injection between cracks and the location of the sensor in this invention;

[0036] Figure 3 This is a physical model of the water injection physical model between cracks in this invention;

[0037] Figure 4This is a diagram of the experimental apparatus of the present invention;

[0038] Figure 5 This is a diagram illustrating the water injection development characteristics of a horizontal well with volumetric fracturing in a tight oil reservoir under a displacement pressure of 6.89 MPa, according to the present invention.

[0039] Figure 6 This invention relates to a pressure cloud map of the water injection process between fractures in a horizontal well undergoing volumetric fracturing in a tight oil reservoir.

[0040] Figure 7 This is a diagram showing the pressure changes at different locations during the water injection process in the fractures of a horizontal well in a tight oil reservoir volumetric fracturing operation, as described in this invention. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and embodiments. The drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

[0042] like Figure 1 As shown, the method for enhancing oil recovery by injecting water into the fractures of a horizontal well undergoing volumetric fracturing in a tight oil reservoir includes the following steps:

[0043] Step 1: Construct a physical model for water injection between fractures in a horizontal well;

[0044] Step 11, Model Selection and Design: Select an outcrop core from the Ordos Basin target area with a permeability of 0.4 mD ± 0.01 mD, and fabricate it into a 50×50×3 cm flat core model. Figure 3 As shown, based on the water injection mode in the fractures of horizontal wells in tight oil reservoirs, a physical model for water injection in the fractures is designed and fabricated based on similarity criteria (geometric similarity, fluid similarity, etc.). The length and width of the hydraulic fractures are designed according to the similarity principle.

[0045] Step 12, Crack Creation: Use a wire EDM machine to cut three cracks, each 46cm long, as shown. Figure 2 The first injection fracture is on the left, the second injection fracture is on the right, and the production fracture is in the middle; a first wellbore and a second wellbore are set above and below the flat core model. Figure 2 The top section is the first wellbore, and the bottom section is the second wellbore, used to simulate the water injection and oil production process in the fractures of a horizontal well in a tight oil reservoir.

[0046] According to the requirements of the physical simulation, a certain number of holes were drilled in the outcrop rock slab. Considering that the hole depth would affect the pressure field measurement, and also to facilitate the fabrication of the experimental flat core model, holes with a depth of 2mm ± 0.1mm were drilled at all pressure measurement points. Finally, the drilled model was cleaned using a blower. Figure 2For example, there are a total of 32 wells. The length of the first and second wells is 40cm. Seven wells are equally spaced on the two wells. The well numbers on the first well are 1, 31, 32, 30, 29, 27, and 28. The well numbers on the second well are 11, 16, 12, 15, 17, 21, and 20. The length of the production fracture is 50cm. The well number 6 is located in the middle of the production fracture. The length of the first and second injection fractures is 50cm. The well number 24 is located in the middle of the second injection fracture. The well numbers 3, 5, 7, 10, 2, 8, 9, and 18 are evenly distributed on the flat core model between the first injection fracture and the production fracture. The well numbers 23, 4, 14, 13, 25, 26, 22, and 19 are evenly distributed on the flat core model between the second injection fracture and the production fracture.

[0047] Step 13: Filling the cracks with sand: Mix 40-mesh quartz sand with special adhesive (A adhesive and B adhesive are mixed in a 1:2 ratio) and fill the cracks evenly. At the same time, seal the top and bottom surfaces of the cracks with marble adhesive to prevent the quartz sand from leaking out.

[0048] Step 14, Pressure Sensor Arrangement: First, use marble adhesive to bond the pressure sensor and the injection-production fracture joint to the corresponding borehole and seal it; then, bond the pressure sensor and marble adhesive to other clean boreholes in this way to arrange and install the pressure sensor.

[0049] Step 15, Model Encapsulation: After assembling the pressure sensor on the outcrop rock core according to the above steps, let the model stand for 2 hours and then move it into the mold for encapsulating the flat rock core model. Then, use special glue to encapsulate the model and wait for the model to cure before removing the mold. At this point, the flat rock core model is complete.

[0050] Step 2: Establish a physical model for water injection into fractured horizontal wells to illustrate the process of bound water.

[0051] Step 21: Perform a pressure measurement point connectivity test on the sealed crack-filled physical model. This mainly tests whether the pressure measurement points on the model are interconnected, and checks for any blockages that occurred during the model fabrication and sealing process at the 32 pressure measurement points. Figure 2-4 As shown; first, inject gas at a certain pressure, leaving only one measuring point connected to a container of water via a hose, and close the other measuring points; if continuous bubbles emerge from the hose inserted in the water, it proves that this pressure measuring point is not blocked; if no continuous bubbles are seen in the hose connected to the water, it indicates that this measuring point is blocked, and it is necessary to use an electric drill to unclog it and check its connectivity again until continuous bubbles appear, indicating that the measuring point is connected; and check the connectivity of all 32 pressure measuring points one by one.

[0052] Step 22: After checking the connectivity of the measuring points, the outcrop rock slab is vacuumed using a multi-point vacuuming device. This process generally involves using a vacuum pump to vacuum the rock slab, measuring pressure at multiple points, and vacuuming for at least 48 hours until the vacuum pump reduces the pressure of the outcrop rock slab to approximately -0.0999 MPa.

[0053] Step 23: When the vacuum pressure of the outcrop rock core reaches about -0.0999 MPa, connect the pre-weighed simulated formation water (mineralization of 50,000 ppm) to the vacuum measuring point and turn off the vacuum pump; the saturation process should last no less than 36 hours, and the simulated formation water in the volumetric flask should be weighed at regular intervals and the mass of the simulated formation water should be recorded.

[0054] Step 24: After 48 hours of saturation of the simulated formation water, once the saturation level of the simulated formation water reaches the target tight oil reservoir requirement, stop the experiment, record the saturated water volume, and unload the outcrop model.

[0055] Step 25: Unload the saturated outcrop rock slab simulating formation water from the saturation device and install it into the high-temperature and high-pressure sealed chamber. At the same time, connect the 32 pressure ports of the flat core model to the wiring ports of the high-temperature and high-pressure sealed chamber. In addition, connect the resistivity measurement line as well. Record the labels of the connection points between the pressure ports on the experimental outcrop flat core model and the high-temperature and high-pressure sealed chamber.

[0056] Step 26: Use pressure port 11 as the injection port, open the valve at pressure port 11, close the valves at other pressure ports, and simultaneously increase the pressure of the displacement pump to 1.0 MPa. Then, introduce kerosene into the intermediate container to perform the venting operation.

[0057] Check the high-temperature and high-pressure sealed chamber for any other substances that may hinder the closure of the chamber opening. Check every detail as thoroughly as possible to ensure that the high-temperature and high-pressure sealed chamber can be closed safely. If the inspection is successful, allow the high-temperature and high-pressure sealed chamber to settle to ensure that the opening of the high-temperature and high-pressure sealed chamber is completely closed with no visible gaps.

[0058] Step 27: After the high-temperature and high-pressure sealed chamber has settled steadily, check for any liquid (usually water or kerosene) leakage. If there is no leakage, close all the pressure measuring valves on the high-temperature and high-pressure sealed chamber.

[0059] Step 28: After closing all 32 pressure connection valves, since the pressure increase is slow in the early stage, the internal pressure of the model is first pressurized to 20.0 MPa using a confining pressure pump; after the ring pressure stabilizes at 20.0 MPa, the oil-driven water process is started, and the experiment is stopped when no water is produced. This part is mainly to establish the process of confining water in the model.

[0060] Step 3: Establish a physical simulation method for water injection between fractures in horizontal wells with volumetric fracturing in tight oil reservoirs;

[0061] Step 31: After establishing bound water in the flat core model, following the principle of injecting water into the fractures of a horizontal well in a tight oil reservoir using volumetric fracturing, and selecting the two outer fractures for injection and the middle fracture for extraction, open the valves at the pressure measuring points on the two injected fractures. Figure 2 (Interfaces 1 and 28), and will extract pressure measurement points on the cracks ( Figure 2 The valve at interface 15 is opened simultaneously, while the valves at the remaining 29 pressure measuring points are closed.

[0062] Step 32: After opening injection valves 1 and 28 and production valve 15, and verifying that everything is correct, begin the water injection development experiment in the fractured horizontal well of the tight oil reservoir. During this process, firstly, set the displacement pump displacement pressure to 6.89 MPa and the production outlet pressure to 0 MPa. Secondly, turn on the automatic data acquisition device to start measuring the outlet fluid. Finally, open the pressure measurement point testing software in the control computer and save the file at all times, with a test interval of 2 minutes. Pay close attention to the phenomena during the experiment and keep detailed records.

[0063] Step 33: Continue sampling during the experiment until the moisture content reaches 90%. Then, turn off the injection displacement pump, close all pressure measuring valves, and end the experiment.

[0064] Experimental results:

[0065] Analysis of the physical simulation results of injection and production in fractured horizontal wells at a displacement pressure of 6.89 MPa, by... Figure 5 As shown in (a), the cumulative fluid and oil production gradually increased with time. Before 48 minutes, during the waterless recovery period, the experimental model produced only oil and no water, with a cumulative oil production of 100.7 ml. Between 48 and 124 minutes, the model was in the oil-water co-production period. After 124 minutes, the model stopped producing oil, with a cumulative total oil production of 117.4 ml. The waterless recovery period accounted for 85.78% of the total oil production, while the oil-water co-production period accounted for 14.22%. The waterless recovery period contributed the most to the oil displacement efficiency. Figure 5 (b) As the injection ratio (PV) increases, the cumulative produced fluid and cumulative produced oil also gradually increase. After displacement reaches 0.263 PV, the oil production no longer increases. Figure 5 (c) shows a rapid decrease in both the liquid production and oil production curves. During the waterless oil recovery stage before 48 minutes, the oil production rate dropped from a maximum of 5.26 ml / min to 0.90 ml / min, a decrease of 82.29%. Figure 5(d) Under the condition of bound water, the oil displacement efficiency of the tight sandstone outcrop plate core model prepared in this experiment was 16.93%. After the model encountered water, the water cut increased rapidly, and the final water cut was 98.48%.

[0066] Figure 6 This image shows pressure cloud maps at different stages during water injection in fractured horizontal wells in tight oil reservoirs. The water injection process in fractured horizontal wells in tight oil reservoirs can establish an effective displacement system. As water injection development progresses, the two ends of the injection fractures advance uniformly towards the production fracture ends, resulting in a linear oil production pattern, which changes the previous point-like water injection situation of traditional well networks. In addition, pressure is continuously transmitted during the displacement process. After 100 minutes of displacement, the influence stops expanding, forming a stable seepage pattern.

[0067] pass Figure 7 It can be seen that the pressure distribution curves at different distances from the injection fracture exhibit a symmetrical "V" shape, indicating that the pressure transmission at both ends of the injection fracture is similar during water injection between horizontal well fractures. Displacement begins at 0 min, and the pressure in the model is in equilibrium, with a consistent pressure distribution at all locations. As water injection between horizontal well fractures progresses, at 2 min, the pressure at a distance of 6.7 cm from the injection fracture is 2.62 MPa, a decrease of 61.9%; at 13.4 cm, the pressure is 1.25 MPa, a decrease of 81.9%; when displacement reaches 4 min, the pressure at a distance of 6.7 cm from the injection fracture is 2.61 MPa, a decrease of 62.1%; at 13.4 cm, the pressure is 1.20 MPa, a decrease of 82.6%; when displacement reaches 45 min, the pressure at a distance of 6.7 cm from the injection fracture is 4.76 MPa. The pressure decreased by 30.9%; at a distance of 13.4 cm from the injection fracture, the pressure was 2.92 MPa, a decrease of 57.6%; when displacement reached 50 min, at a distance of 6.7 cm from the injection fracture, the pressure was 4.80 MPa, a decrease of 30.3%; at a distance of 13.4 cm from the injection fracture, the pressure was 2.99 MPa, a decrease of 56.6%; thereafter, the pressure at a distance of 6.7 cm from the injection fracture remained basically unchanged at 4.90 MPa, and the pressure at a distance of 13.4 cm from the injection fracture was also the same at 3.12 MPa; the pressure transmission tended to stabilize, and the trend of change tended to be consistent.

[0068] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for enhancing oil recovery by injecting water into fractured spaces in a horizontal well of a tight oil reservoir via volumetric fracturing, characterized in that... Includes the following steps: Step 1: Construct a physical model for water injection between fractures in a horizontal well; Specifically, it includes: Step 11: Select the outcrop core of the target block and process it into a flat core model; Step 12: Cut out the first injection fracture and the second injection fracture on the flat core model, and cut out the production fracture in the middle; drill several holes on the first injection fracture, the second injection fracture, the production fracture, the first wellbore, the second wellbore, and in the area formed by the first injection fracture, the second injection fracture, the production fracture, the first wellbore, and the second wellbore. Step 13: Fill the cracks with a mixture of quartz sand and AB glue, and then cover them with marble glue. Step 14: Install a pressure sensor at the opening; Step 15: After letting the flat core model stand for 2 hours, transfer it to the sealing mold; Step 2: Establish a physical model for water injection into fractured horizontal wells to illustrate the process of bound water. Specifically, it includes: Step 21: Test the connectivity and sealing of each opening; Step 22: Perform a vacuum test on the flat core model; Step 23: When the vacuum pressure reaches -0.0999MPa, connect the simulated formation water to the vacuum measurement point and turn off the vacuum pump; the saturation process should last no less than 36 hours, and the simulated formation water should be weighed and the mass of the water recorded at regular intervals. Step 24: After the simulated formation water saturation reaches the target tight oil reservoir requirement, stop the experiment and record the saturation water volume; Step 25: Remove the flat core model from the saturation device and install it into the high-temperature and high-pressure sealed chamber, and connect all pressure interfaces to the wiring ports of the high-temperature and high-pressure sealed chamber. Step 26: Open the pressure interface valve at the junction of the first injection fracture and the second wellbore, close the other pressure connection valves, increase the displacement pump pressure to 1.0 MPa, introduce kerosene into the intermediate container to perform the venting operation, and then allow the high-temperature and high-pressure sealed chamber to settle. Step 27: After confirming that there is no leakage in the high-temperature and high-pressure sealed chamber, close the pressure interface valve at the junction of the first injection fracture and the second wellbore; Step 28: Use a confining pressure pump to pressurize the internal pressure of the flat core model to 20.0 MPa, and open and close the injection port, the extraction port and the pressure measurement point of the flat core model in a planar cross pattern; Step 3: Establish a physical simulation method for water injection between fractures in horizontal wells with volumetric fracturing in tight oil reservoirs; Specifically, it includes: Step 31: After establishing the bound water in the flat core model, open the valves at the two pressure measuring points at the intersection of the first injection fracture, the second injection fracture, and the first wellbore; open the valve at the pressure measuring point at the intersection of the production fracture and the second wellbore; and close the valves at other pressure measuring points. Step 32: Set the displacement pump displacement pressure to 6.89 MPa and the outlet pressure to 0 MPa; then, turn on the automatic data acquisition device to start metering the outlet liquid; and save the test data in time using the pressure measurement point test software. Step 33: When the moisture content reaches 90%, turn off the injection pump pressure and close all pressure measuring valves.

2. The method for enhancing oil recovery by injecting water into fractured spaces in a horizontal well with volumetric fracturing in a tight oil reservoir according to claim 1, characterized in that, The permeability of the outcrop core is 0.4 mD ± 0.01 mD.

3. A system for enhancing oil recovery by injecting water into fractured spaces in a horizontal well of a tight oil reservoir via volumetric fracturing, characterized in that: include: Memory is used to store instructions that can be executed by the processor; A processor for executing instructions to implement the method of enhancing oil recovery by injecting water into fractured horizontal wells in tight oil reservoirs as described in any one of claims 1-2.

4. A computer-readable medium storing computer program code, characterized in that, The computer program code, when executed by a processor, implements the method for enhancing oil recovery by injecting water into the fractures of a horizontal well in a tight oil reservoir using volumetric fracturing as described in any one of claims 1-2.

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