A device and method for simulating the temporary holding effect of a temporary holding agent during hydraulic fracturing

Abstract

The present invention discloses a device and method for simulating the temporary blocking effect of a temporary blocking agent during hydraulic fracturing. A rock core is installed in a rock core holder. The fracturing fluid injection port of the rock core holder is connected to the fracturing fluid injection device. The fracturing fluid injection port is provided with a first pressure gauge and a first valve in sequence along the flow direction of the fracturing fluid. The confining pressure application port of the rock core holder is connected to the confining pressure application device. The confining pressure application port of the rock core holder is provided with a second pressure gauge and a second valve in the flow direction of the liquid. The fracturing fluid outlet of the rock core holder is provided with a third pressure gauge and a third valve in sequence along the flow direction of the liquid. The rock core includes a steel rock core and a powdered stainless steel sintered sheet. A main fracture channel is opened at the axis of the steel rock core. The powdered stainless steel sintered sheet is provided at one end of the steel rock core to block the outlet end of the main fracture channel. The present invention can simulate the temporary blocking effect of a temporary blocking agent under different main fracture positions and aperture conditions, thereby providing guidance for the optimized design of temporary blocking agents on-site in oil fields.

Description

Technical Field

[0001] The present invention relates to the field of petroleum engineering oil and gas field development, and in particular to a device and method for simulating the temporary holding effect of a temporary holding agent in a hydraulic fracturing process. Background Art

[0002] Hydraulic fracturing technology is currently one of the most important production-increasing technologies for developing unconventional oil and gas reservoirs. This technology mainly uses the rock-breaking effect of high-pressure liquid to form a high-conductivity sand-filled fracture in the reservoir, thereby significantly improving the seepage capacity of oil and gas.

[0003] With the development of fracturing technology, conventional hydraulic fracturing can no longer meet the needs of oil fields. In recent years, oilfield engineers have proposed a method called temporary blocking and fracturing. This method involves adding a temporary blocking agent to the fracturing fluid. Once the temporary blocking agent migrates into the main fracture, it undergoes a physical and chemical change, temporarily blocking the main fracture channel, increasing the pressure in the main fracture, and forcing a network of branching fractures into the rock wall of the main fracture, ultimately achieving the goal of volume fracturing. The key to this method is to study the temporary blocking and pressure-holding process of the temporary blocking agent at different locations in the main fracture channel and to optimize the formulation and dosage of the temporary blocking agent. However, there are currently few reports on experimental simulation methods for temporary blocking and fracturing. Simulating the process of temporary blocking and pressure-holding to create branching fractures indoors, thereby optimizing the formulation and dosage of the temporary blocking agent, has become a bottleneck technical issue currently restricting this method. Summary of the Invention

[0004] In order to solve the problem that indoor experiments cannot simulate the temporary blocking process of fracture creation, the present invention proposes a device and method for simulating the temporary blocking effect of a temporary blocking agent during hydraulic fracturing. The present invention can simulate the temporary blocking effect of a temporary blocking agent under different main fracture positions and aperture conditions, thereby providing guidance for the optimal design of temporary blocking agents on site in oil fields.

[0005] In order to achieve the above object, the technical solution of the present invention is:

[0006] A device for simulating the temporary choking effect of a temporary choking agent during hydraulic fracturing, comprising a fracturing fluid injection device, a rock core, a core holder, and a confining pressure applying device. The rock core is installed in the core holder, a fracturing fluid injection port of the core holder is connected to the fracturing fluid injection device, a first pressure gauge and a first valve are sequentially provided at the fracturing fluid injection port of the core holder along the flow direction of the fracturing fluid, a confining pressure applying port of the core holder is connected to the confining pressure applying device, a second pressure gauge and a second valve are provided at the confining pressure applying port of the core holder along the flow direction of the liquid, and a third pressure gauge and a third valve are sequentially provided at the fracturing fluid outlet of the core holder along the flow direction of the liquid.

[0007] The core comprises a steel core and a powdered stainless steel sintered sheet. A main crack channel is opened at the axis of the steel core. The powdered stainless steel sintered sheet is arranged at one end of the steel core and blocks the outlet end of the main crack channel.

[0008] Preferably, the steel core is divided into two halves along the axis.

[0009] Preferably, the steel core and the powdered stainless steel sintered sheet are connected to form an integral structure via a coating layer, and the coating layer coats the side surfaces of the steel core and the powdered stainless steel sintered sheet.

[0010] Preferably, the crack channel is a rectangular channel.

[0011] Preferably, the length of the steel core is 2 cm to 10 cm, the radius is 1.1 cm to 1.3 cm, the width of the fracture channel is 0.2 cm to 1 cm, and the height is 0.8 cm to 1.6 cm.

[0012] Preferably, the powdered stainless steel sintered sheet has a filtration accuracy of 1 μm-200 μm and a thickness of 1 cm-2.5 cm.

[0013] Preferably, when simulating the temporary blocking effect of the temporary blocking agent at the tip of the main crack, a powder stainless steel sintered sheet with a filtration accuracy of 1μm-15μm is used; when simulating the temporary blocking effect of the temporary blocking agent at the middle position of the main crack, a powder stainless steel sintered sheet with a filtration accuracy of 15μm-200μm is used.

[0014] Preferably, the fracturing fluid injection device includes a double-cylinder constant speed and constant pressure pump and an intermediate liquid tank, the outlet of the double-cylinder constant speed and constant pressure pump is connected to the inlet of the intermediate liquid tank, the outlet of the intermediate liquid tank is connected to the fracturing fluid injection port end of the core clamp, the inlet and outlet of the intermediate liquid tank are both provided with valves, and the confining pressure applying device adopts an annular pressure pump.

[0015] The present invention also provides a method for simulating the temporary holding effect of a temporary holding agent during hydraulic fracturing. The method is performed using the device for simulating the temporary holding effect of a temporary holding agent during hydraulic fracturing as described above, and includes the following steps:

[0016] Load the core into the core holder so that the powdered stainless steel sintered sheet is located toward the fracturing fluid outlet end of the core holder;

[0017] After the core is installed, confining pressure is applied to the core holder;

[0018] After applying a preset confining pressure to the core holder, fracturing fluid is injected into the core holder to conduct a temporary holding simulation experiment. During the temporary holding simulation experiment, the pressure data at the fracturing fluid inlet and outlet of the core holder, as well as the fluid output at the fracturing fluid outlet of the core holder, are recorded in real time.

[0019] The collected data are used to draw the curve corresponding to the temporary holding pressure and time, as well as the curve of the relationship between the temporary holding layer loss flow and time, and the curve changes are analyzed to obtain the temporary holding performance of the temporary holding agent.

[0020] The present invention has the following beneficial effects:

[0021] In the technical solution proposed by the present invention, by setting main crack channels of different sizes and using powder stainless steel sintered sheets with different filtration precisions, it is possible to simulate the temporary blocking seam-making experiment under different main crack openings and main crack temporary blocking positions; therefore, the present invention can be used to evaluate the temporary blocking effects of different types of temporary blocking agents, thereby providing guidance for the optimal design of temporary blocking agents. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG1(a) is an axial schematic diagram of a steel core according to the present invention; FIG1(b) is a longitudinal cross-sectional diagram of a steel core according to the present invention;

[0023] Figure 2 This is a schematic diagram of the powder stainless steel sintered sheet used in the present invention;

[0024] Figure 3 This is a schematic diagram of the core for assembling a temporary holding simulation experiment according to the present invention;

[0025] Figure 4 Schematic diagram of a device for simulating the temporary holding effect of a temporary holding agent during hydraulic fracturing according to the present invention;

[0026] Figure 5(a) is a schematic diagram of the principle of the temporary holding simulation experiment (schematic diagram of the principle of creating branch fractures by temporary holding in the main fracture channel); Figure 5(b) is a schematic diagram of the principle of the temporary holding simulation experiment (schematic diagram of the principle of creating branch fractures by temporary holding at the crack tip of the main fracture channel);

[0027] Figure 6 This is a graph showing the temporary holding effect of the modified degradable fiber temporary holding agent in Example 1 of the present invention;

[0028] Figure 7 This is a curve diagram of the temporary holding effect of the modified super absorbent resin in Example 2 of the present invention.

[0029] In the figure, 1-steel core, 1-1-main fracture channel, 2-powdered stainless steel sintered sheet, 4-double-cylinder constant speed and constant pressure pump, 5-intermediate liquid tank, 6-valve, 7-pressure gauge, 8-core holder, 9-measuring cylinder, 10-annular pressure pump, 11-main fracture, 12-branch fracture, 13-temporary blocking agent, 14-wellbore. DETAILED DESCRIPTION

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] See Figure 1(a), Figure 1(b), Figures 2 to 4The device for simulating the temporary holding effect of the temporary holding agent in the hydraulic fracturing process of the present invention comprises a fracturing fluid injection device, a core, a core holder 8 and a confining pressure applying device, wherein the core is installed in the core holder 8, the fracturing fluid injection device comprises a double-cylinder constant speed and constant pressure pump 4 and an intermediate liquid tank 5, the outlet of the double-cylinder constant speed and constant pressure pump 4 is connected to the inlet of the intermediate liquid tank 5, the fracturing fluid injection port end of the core holder 8 is connected to the outlet of the intermediate liquid tank 5, the inlet and outlet of the intermediate liquid tank 5 are both provided with valves 6, the core holder The fracturing fluid injection port of the core holder 8 is provided with a first pressure gauge and a first valve in sequence along the flow direction of the fracturing fluid. The confining pressure applying device adopts an annular pressure pump 10. The confining pressure applying port of the core holder 8 is connected to the outlet of the annular pressure pump 10. The confining pressure applying port of the core holder 8 is provided with a second pressure gauge and a second valve in the flow direction of the liquid. The fracturing fluid outlet of the core holder 8 is provided with a third pressure gauge and a third valve in sequence along the flow direction of the liquid. The pipeline outlet of the fracturing fluid outlet of the core holder 8 is provided with a measuring cylinder 9.

[0032] The core includes a steel core 1 and a powdered stainless steel sintered sheet 2. A main fracture channel 1-1 is opened at the axis of the steel core 1. The main fracture channel 1-1 is used to install a temporary blocking agent. The powdered stainless steel sintered sheet 2 is arranged at one end of the steel core 1 and blocks the outlet end of the main fracture channel 1-1.

[0033] In order to ensure the accuracy of the relative position of the steel core 1 and the powdered stainless steel sintered sheet 2 when the core is installed in the core holder 8, and to prevent the steel core 1 and the powdered stainless steel sintered sheet 2 from being misaligned during placement in the core holder 8, thereby affecting the displacement effect, the steel core 1 and the powdered stainless steel sintered sheet 2 can be connected into an integral structure through a coating layer, and the coating layer is coated on the sides of the steel core 1 and the powdered stainless steel sintered sheet 2. Generally, a heat sealing gun can be used to seal the steel core and the powdered stainless steel sintered sheet 2. In order to facilitate the filling of the temporary blocking agent in the main fracture channel 1-1, the present invention divides the steel core 1 into two halves along the axis. After the two halves of the steel core 1 are filled with the temporary blocking agent, they are assembled into a whole and then sealed with the powdered stainless steel sintered sheet 2 using a heat sealing gun.

[0034] In order to better simulate the main fracture, the present invention sets the fracture channel 1-1 as a rectangular channel. Referring to Figures 1(a) and 1(b), the length D of the steel core 1 is 2 cm to 10 cm, the radius R is 1.1 cm to 1.3 cm, and the width W of the fracture channel 1-1 is equal to the opening of the main fracture, with a width of 0.2 cm to 1 cm and a height of 0.8 cm to 1.6 cm.

[0035] When selecting the powder stainless steel sintered sheet 2, the powder stainless steel sintered sheet 2 is resistant to acid and alkali corrosion, high temperature resistance of 600°C, filtration accuracy of 1μm-200μm, and thickness of 1cm-2.5cm; different sintered sheets should be used to simulate different main crack positions. When simulating the temporary blocking effect of the temporary blocking agent at the tip of the main crack (see Figure 5(b)), a powder stainless steel sintered sheet 2 with high filtration accuracy (1μm-15μm) and slow fluid loss rate should be used; when simulating the temporary blocking effect of the temporary blocking agent at the middle position of the main crack (see Figure 5(a)), a sintered sheet with low filtration accuracy (15μm-200μm) and fast fluid loss rate should be used.

[0036] The working method of the device for simulating the temporary holding effect of the temporary holding agent during hydraulic fracturing of the present invention comprises the following steps:

[0037] Step 1: Assemble the temporary blocking simulation experiment core: evenly spread the temporary blocking agent used in the study in the main fracture channel 1-1 inside the steel core as shown in Figure 1 (a) and Figure 1 (b), then fasten the two halves of the steel core together, and use a heat sealing gun to seal the steel core 1 and the powdered stainless steel sintered sheet 2 along the axial direction (assembly diagram as shown in Figure 1). Figure 3 shown).

[0038] Step 2: Connect pipelines and assemble instruments: Use pipelines to connect the fracturing fluid injection device, core holder 8 and confining pressure application device, check whether the pipelines and instruments are sealed and leak-proof under displacement status, and check whether the pressure gauge and valve are normal.

[0039] Step 3: Clamp the temporary holding simulation test core and apply confining pressure: Place the temporary holding simulation test core assembled in Step 1 into the core holder and install the instrument. Then, open the annular pressure pump valve and use the annular pressure pump to apply confining pressure to the core holder. The confining pressure applied by the annular pressure pump must not be lower than the estimated holding pressure of the temporary holding agent, otherwise the evaluation of the temporary holding agent's holding effect will be inaccurate. When installing the core, the end of the powdered stainless steel sintered sheet 2 should correspond to the fracturing fluid outlet, while the end of the steel core should be at the fracturing fluid inlet, thereby simulating the process of fracturing fluid migration from the front end to the back end of the main fracture channel.

[0040] Step 4: Add fracturing fluid and start the temporary holding simulation experiment: Add the fracturing fluid to the intermediate liquid tank, then open the valves of the displacement pump, core clamp and intermediate liquid tank, set the constant flow displacement condition, and conduct the temporary holding simulation experiment.

[0041] Step 5: Record the temporary holding pressure and filtration flow rate, and analyze and study the experimental data: During the temporary holding simulation experiment, record the pressure data corresponding to the pressure gauges at the fracturing fluid inlet and pressure liquid outlet, and the liquid volume in the measuring cylinder in real time; use the collected data to draw the curve corresponding to the temporary holding pressure and time, and the relationship curve between the temporary holding layer filtration flow rate and time; finally, analyze the curve changes and study the temporary holding performance of the temporary holding agent.

[0042] The principle of the present invention is as follows: As shown in FIG5(a) and FIG5(b), during the hydraulic fracturing process, the temporary blocking agent temporarily blocks the fracture in the fracture and is divided into two situations:

[0043] The first case: As shown in Figure 5(a), the temporary pressure agent migrates to a certain position in the middle of the main fracture channel and then begins to suppress pressure to create branch fractures;

[0044] The second case: As shown in Figure 5(b), the temporary pressure agent migrates to the tip of the main fracture channel and then begins to suppress pressure to create branch fractures;

[0045] The dosage, formulation, and holding pressure of the temporary blocking agent will vary. Based on these two situations, the present invention uses hollow steel cores of different widths to simulate main fracture channels of different openings, and uses the different filtration characteristics of sintered plates to simulate the temporary blocking of the temporary blocking agent at different locations. Sintered plates with high filtration accuracy and low filtration volume can simulate the blocking effect of the main fracture tip on the fluid, thereby simulating the temporary blocking experiment of the temporary blocking agent at the main fracture tip. Sintered plates with high filtration volume can simulate the situation where the fluid in the middle of the main fracture has no blocking effect, thereby simulating the temporary blocking experiment of the temporary blocking agent in the middle of the main fracture.

[0046] Example 1

[0047] The present invention was used to evaluate a modified degradable fiber temporary blocking agent used in an oil field. The specific steps are as follows:

[0048] (1) A steel core with a length of 5 cm and an R of 1.25 cm was selected as the simulated rock sample. The width W of its internal groove was 0.5 cm and the height L was 1.2 cm. A sintered sheet with a thickness of 2 cm and a filtration accuracy of 10 μm was selected to simulate the temporary blocking effect of the temporary blocking agent at the end of the main fracture.

[0049] (2) The modified degradable fiber is evenly laid in the groove inside the steel core, and then the two halves of the steel core are fastened together, and the steel core and the sintered sheet are sealed together along the axis using a heat sealing gun.

[0050] (3) Connect the pipelines, assemble the instrument, and ensure that there is no leakage in the pipeline under a stable pressure of 10 MPa. Then put the assembled temporary holding simulation experimental core into the core holder and install the instrument. Open the valve of the annular pressure pump and use the annular pressure pump to apply a confining pressure of 50 MPa to the core holder.

[0051] (4) Slickwater fracturing fluid with a viscosity of 5.0 mPa·s was added to the intermediate container, and then the valves of the displacement pump, core holder, and intermediate liquid tank were opened. The displacement condition was set to a constant flow rate of 15 mL / min, and a temporary holding simulation experiment was carried out.

[0052] (5) The experimental process records the curve of the pressure difference between the two ends of the core holder over time. Figure 6 shown.

[0053] from Figure 6 It can be seen that the initial short-term pressure rises rapidly to 34.5 MPa after the fracturing fluid is injected. After a five-hour period of stabilization, the pressure gradually decreases as the modified biodegradable fiber degrades, and finally the temporary pressure difference significantly decreases to 2 MPa. Therefore, it can be seen that the temporary pressure agent can quickly increase the pressure in the fracture. Its temporary pressure strength should be 35 MPa, and it can maintain a stable temporary pressure for 5 hours, indicating an overall good temporary pressure effect.

[0054] Example 2

[0055] The present invention was used to evaluate the modified superabsorbent resin temporary blocking agent used in the Chang 7 reservoir of another oil field. The specific steps are as follows:

[0056] (1) A steel core with a length of 10 cm and an R of 1.22 cm was selected as the simulated rock sample. The width W of its internal groove was 0.7 cm and the height L was 1.3 cm. A sintered sheet with a thickness of 2 cm and a filtration accuracy of 100 μm was selected to simulate the temporary blocking effect of the temporary blocking agent at the end of the main fracture.

[0057] (2) The modified super absorbent resin is evenly spread in the groove inside the steel core, and then the two halves of the steel core are fastened together, and the steel core and the sintered sheet are sealed along the axial direction using a heat sealing gun.

[0058] (3) Connect the pipelines, assemble the instrument, and ensure that there is no leakage in the pipeline under a stable pressure of 15 MPa. Then put the assembled temporary holding simulation experimental core into the core holder and install the instrument. Open the valve of the annular pressure pump and use the annular pressure pump to apply a confining pressure of 75 MPa to the core holder.

[0059] (4) Slickwater fracturing fluid with a viscosity of 1.2 mPa·s was added to the intermediate container, and then the valves of the displacement pump, core holder, and intermediate liquid tank were opened. The displacement condition was set to a constant flow rate of 30 mL / min, and a temporary holding simulation experiment was carried out.

[0060] (5) The experimental process records the curve of the pressure difference between the two ends of the core holder over time. Figure 7 shown.

[0061] from Figure 7As can be seen, the initial short-term holding pressure of the fracturing fluid increased to 70 MPa within two hours of injection. After stabilizing for 10 hours, the pressure gradually decreased as the modified superabsorbent resin softened, and finally the holding pressure differential gradually decayed to 2.3 MPa. This shows that the temporary holding agent has a strong holding capacity, reaching a holding strength of up to 70 MPa, making it suitable for unconventional reservoirs with relatively close biaxial stress differences. Its holding time can be sustained for 10 hours, demonstrating an overall excellent holding effect.

Claims

1. A device for simulating the temporary holding effect of a temporary holding agent during hydraulic fracturing, characterized in that: The invention comprises a fracturing fluid injection device, a core, a core holder (8) and a confining pressure applying device, wherein the core is installed in the core holder (8), the fracturing fluid injection port end of the core holder (8) is connected to the fracturing fluid injection device, the fracturing fluid injection port end of the core holder (8) is provided with a first pressure gauge and a first valve in sequence along the flow direction of the fracturing fluid, the confining pressure applying port of the core holder (8) is connected to the confining pressure applying device, the confining pressure applying port of the core holder (8) is provided with a second pressure gauge and a second valve in the flow direction of the liquid, and the fracturing fluid outlet end of the core holder (8) is provided with a third pressure gauge and a third valve in sequence along the flow direction of the liquid; The core comprises a steel core (1) and a powdered stainless steel sintered sheet (2); a main fracture channel (1-1) is opened at the axis of the steel core (1); the powdered stainless steel sintered sheet (2) is arranged at one end of the steel core (1) and blocks the outlet end of the main fracture channel (1-1); The steel core (1) is divided into two halves along the axis; The main crack channel (1-1) is a rectangular channel; the main crack channel (1-1) is filled with a temporary blocking agent.

2. The device for simulating the temporary holding effect of a temporary holding agent during hydraulic fracturing according to claim 1, characterized in that: The steel core (1) and the powdered stainless steel sintered sheet (2) are connected to form an integral structure via a coating layer, and the coating layer coats the side surfaces of the steel core (1) and the powdered stainless steel sintered sheet (2).

3. The device for simulating the temporary holding effect of a temporary holding agent during hydraulic fracturing according to claim 1, characterized in that: The length of the steel core (1) is 2 cm to 10 cm, the radius is 1.1 cm to 1.3 cm, the width of the main fracture channel (1-1) is 0.2 cm to 1 cm, and the height is 0.8 cm to 1.6 cm.

4. The device for simulating the temporary holding effect of a temporary holding agent during hydraulic fracturing according to claim 1, characterized in that: The powdered stainless steel sintered sheet (2) has a filtering accuracy of 1 μm-200 μm and a thickness of 1 cm-2.5 cm.

5. The device for simulating the temporary holding effect of a temporary holding agent during hydraulic fracturing according to claim 4, characterized in that: When simulating the temporary holding effect of the temporary holding agent at the main crack tip, a powdered stainless steel sintered sheet (2) with a filtration accuracy of 1 μm-15 μm is used; when simulating the temporary holding effect of the temporary holding agent at the middle position of the main crack, a powdered stainless steel sintered sheet (2) with a filtration accuracy of 15 μm-200 μm is used.

6. The device for simulating the temporary holding effect of a temporary holding agent during hydraulic fracturing according to claim 1, characterized in that: The fracturing fluid injection device comprises a double-cylinder constant-speed constant-pressure pump (4) and an intermediate liquid tank (5), the outlet of the double-cylinder constant-speed constant-pressure pump (4) is connected to the inlet of the intermediate liquid tank (5), the outlet of the intermediate liquid tank (5) is connected to the fracturing fluid injection port end of the core holder (8), the inlet and outlet of the intermediate liquid tank (5) are both provided with valves (6), and the confining pressure applying device adopts an annular pressure pump (10).

7. A method for simulating the temporary holding effect of a temporary holding agent during hydraulic fracturing, characterized in that: The method is carried out using the device for simulating the temporary holding effect of a temporary holding agent in a hydraulic fracturing process according to any one of claims 1 to 6, and includes the following steps: The core is placed in the core holder (8) so that the powdered stainless steel sintered sheet (2) is located toward the fracturing fluid outlet end of the core holder (8); After the core is installed, a confining pressure is applied to the core holder (8); After applying a preset confining pressure to the core holder (8), a fracturing fluid is injected into the core holder (8) to conduct a temporary holding simulation experiment. During the temporary holding simulation experiment, the pressure data at the fracturing fluid inlet and outlet of the core holder (8) and the fluid output at the fracturing fluid outlet of the core holder (8) are recorded in real time; The collected data are used to draw the curve corresponding to the temporary holding pressure and time, as well as the curve of the relationship between the temporary holding layer loss flow and time, and the curve changes are analyzed to obtain the temporary holding performance of the temporary holding agent.

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