Shale oil reservoir volume fractured horizontal well'stuffy-drainage-mining 'integrated physical simulation method

Abstract

The invention discloses a shale oil reservoir volume fractured horizontal well'stuffiness-drainage-production 'integrated physical simulation method, which comprises the following steps: drilling a shale oil reservoir full-diameter plunger rock sample, and completing rock sample pretreatment; wax-sealing the pretreated rock sample, and vacuumizing and pressurizing to saturate heavy water; displacing the saturated heavy water rock sample with the compounded in-situ crude oil until a bound water state; wax seals are removed, quartz sand is laid on the end faces of the rock samples, the rock samples are spliced to form a volume fracturing horizontal well physical model, and the volume fracturing horizontal well physical model is loaded into a rock sample holder; heavy water is pumped into the inlet end of the rock sample holder and pressurized, the inlet end is closed, and the well closing process after fracturing is simulated; and opening the inlet end of the rock sample holder, and simulating flowback production after fracturing. According to the experimental method, the'stuffy-drainage-mining 'physical process of the shale oil volume fractured horizontal well can be restored, fluid imbibition, flowing and occurrence rules are researched, and efficient development of shale oil reservoirs is guided.

Description

TECHNICAL FIELD

[0001] The present application relates to a shale reservoir volume fracturing horizontal well "soaking-discharge-production" integrated physical simulation method, belonging to the technical field of oil and gas field development. BACKGROUND

[0002] China's shale oil reservoir resources are abundant, mainly distributed in Songliao Basin, Ordos Basin, Junggar Basin and other regions. Shale oil reservoirs have the characteristics of low porosity and low permeability, and the effect of traditional development methods is limited. Volume fracturing technology has become a key means. Through horizontal well volume fracturing, a complex fracture network is formed to improve the permeability of shale oil reservoirs and the producing degree of reserves, significantly improving the single well production of shale oil reservoirs and ensuring China's energy security.

[0003] At present, the "soaking-discharge-production" development mode of shale oil reservoir horizontal well volume fracturing has become the mainstream. It is extremely important to obtain the fluid imbibition, flow and occurrence regularity in the "soaking-discharge-production" process for formulating a reasonable production system. Indoor experiments are the main technical means to obtain the fluid imbibition, flow and occurrence regularity in the "soaking-discharge-production" process. However, current indoor experiments mainly focus on single small rock sample static experiments or certain single stage experiments, without restoring the "soaking-discharge-production" physical whole process, and cannot systematically explain the fluid imbibition, flow and occurrence regularity in the whole physical process. For example, the Chinese patent "Shale oil reservoir static imbibition capacity characterization method" with publication number CN118376555A proposes a shale oil reservoir static imbibition capacity characterization method, which obtains the shale oil reservoir imbibition capacity through experiments. However, the experiment is limited to a single small rock sample, cannot restore the "soaking-discharge-production" physical whole process, and cannot systematically study the fluid imbibition, flow and occurrence regularity in the whole physical process, which has certain limitations.

[0004] The Chinese patent "Shale imbibition oil and gas production capacity quantitative evaluation device and method under reservoir conditions" with publication number CN119558050A provides a shale reservoir imbibition oil and gas production capacity evaluation device and method, which can more conveniently obtain the shale reservoir imbibition oil and gas production capacity and imbibition characteristics. However, the experiment is limited to a single small rock sample, cannot restore the "soaking-discharge-production" physical whole process, and cannot systematically study the fluid imbibition, flow and occurrence regularity in the whole physical process, which has certain limitations. SUMMARY

[0005] In view of the above problems, the present application provides a shale oil reservoir volume fracturing horizontal well soaking-production integrated physical simulation experiment method.

[0006] The present application aims to restore the "soaking-discharge-production" development mode physical process of shale oil reservoir horizontal well volume fracturing, systematically study the fluid imbibition, flow and occurrence regularity, guide the formulation of a reasonable development plan and production system, and improve the shale oil reservoir development effect.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: "suffocation-discharge-collection".

[0008] Step 1: Drill full-diameter plunger rock samples from the shale oil reservoir and complete the rock sample pretreatment;

[0009] Step 2: Based on the rock sample pretreated in Step 1, after sealing the through-holes with wax, vacuum and pressurize with saturated heavy water;

[0010] Step 3: Based on the saturated heavy water rock sample obtained in Step 2, use formation degassed crude oil to displace the saturated heavy water rock sample until the bound water state is reached, and remove the wax seal.

[0011] Step 4: Based on the rock sample that has reached the bound water state in Step 3, quartz sand is laid on its end face, the rock samples are spliced ​​together to form a physical model of a volumetric fracturing horizontal well, and a rock sample holder is installed.

[0012] Step 5: Based on Step 4, after pumping heavy water and pressurizing it into the inlet of the rock sample holder, seal the inlet of the rock sample holder to simulate the well shut-in process after fracturing;

[0013] Step Six: After simulating the well blockage process achieved in Step Five, open the inlet end of the rock sample holder to simulate the post-fracturing flowback production process.

[0014] Beneficial effects of the invention

[0015] This invention provides an integrated physical simulation method for the "shut-drain-production" process of horizontal wells in shale oil reservoirs via volumetric fracturing. Combining the construction of a physical model of full-diameter rock samples and nuclear magnetic resonance dynamic monitoring technology, it obtains the fluid permeation and flow patterns throughout the entire process of well shut-in, flowback, and production after fracturing, establishing a physical simulation system that realistically recreates field conditions. This method overcomes the shortcomings of existing experimental techniques that only target a single stage or small rock samples and cannot systematically reveal the dynamic patterns of the entire development cycle. It has significant guiding significance for the design of fracturing schemes, optimization of well shut-in systems, flowback control, and development adjustments in shale oil reservoirs. Attached Figure Description

[0016] Figure 1 Figure for the abstract

[0017] Figure 2 Establish NMR T2 spectrum curves for the bound water process in A-1

[0018] Figure 3 Establishing the nuclear magnetic resonance T2 spectrum curve of the bound water process for A-2

[0019] Figure 4 Establishing the nuclear magnetic resonance T2 spectrum curve of the bound water process for A-3

[0020] Figure 5Establishing the nuclear magnetic resonance T2 spectrum curve of the bound water process for A-4

[0021] Figure 6 Schematic diagram of the physical model of a horizontal well with volumetric fracturing

[0022] Figure 7 T2 NMR spectrum curves before and after the well blockage process in simulation A-1.

[0023] Figure 8 T2 NMR spectrum curves before and after the A-2 simulated well blockage process.

[0024] Figure 9 T2 NMR spectrum curves before and after the A-3 simulated well blockage process.

[0025] Figure 10 T2 NMR spectrum curves before and after the A-4 simulated well blockage process.

[0026] Figure 11 T2 NMR spectrum curves before and after the A-1 simulated flowback mining process.

[0027] Figure 12 T2 NMR spectrum curves before and after the A-2 simulated flowback mining process.

[0028] Figure 13 T2 NMR spectrum curves before and after the A-3 simulated flowback mining process.

[0029] Figure 14 The T2 NMR spectrum curves before and after the A-4 simulated flowback mining process. Detailed Implementation

[0030] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0031] In one embodiment, an integrated physical simulation method for "suffocation-discharge-production" in a shale oil reservoir volumetric fracturing horizontal well includes the following steps:

[0032] Step 1: Drill four full-diameter plunger rock samples with a reservoir length L of 15cm and a diameter d of 10cm from well A in a shale oil reservoir. These samples are numbered A-1, A-2, A-3, and A-4, respectively. After washing and drying the samples, measure the basic physical properties such as the mass m, permeability k, and porosity φ of the rock samples.

[0033] Heat shrink sleeves were wrapped around the sides of four full-diameter rock samples, and then heated to ensure the sleeves tightly enclosed the samples.

[0034] A 2.5cm diameter drill bit was selected and drilled through the rock sample from the center point of the full diameter end face along the length L direction to obtain a through-hole with a length L' of 15cm and a diameter d' of 2.5cm. The wellbore of the horizontal well was simulated by volumetric fracturing. Rock particles inside the well were removed to complete the rock sample pretreatment.

[0035] Step 2: Place the four pre-treated full-diameter rock samples upright with the bottom iron sheet tightly attached. Heat and melt the solid microcrystalline wax, and pour it into the channel from the top until the channel is completely filled. After the microcrystalline wax has completely cooled and solidified, remove the bottom iron sheet and sand the two ends of the full-diameter rock samples to make the end surfaces smooth and flat without any wax protrusions.

[0036] After the rock sample was sealed with wax, it was placed in a pressure vessel and evacuated for 5 hours. Then, the pressure vessel was filled with heavy water and the pressure inside the pressure vessel was increased to 25 MPa. The pressure was maintained at 25 MPa for 72 hours. The pressure inside the pressure vessel was then released, and the full-diameter rock sample sealed with wax and saturated with heavy water was taken out.

[0037] Step 3: Place four wax-sealed full-diameter rock samples saturated with heavy water individually in a sample holder. Set the holder confining pressure to 7.5 MPa, the back pressure at the holder outlet to 2 MPa, and the displacement pressure of the formation degassed crude oil at the holder inlet to 5 MPa. Displace the heavy water with the formation degassed crude oil, and record the water production q0 at the outlet and the liquid output q1 from the displacement pump. Due to the saturation of heavy water, the initial NMR T2 curve signal is 0. Measure the NMR T2 spectrum curve of the rock samples every 12 hours. The NMR T2 spectrum curve of rock sample A-1 at 48 hours coincides with the NMR spectrum curve measured at 36 hours, and the NMR T2 spectrum curve remains unchanged, indicating that the rock sample is in a bound water state. The time to establish bound water for rock samples A-2, A-3, and A-4 is 36 hours, 48 ​​hours, and 60 hours, respectively. The NMR T2 spectrum curves of the four full-diameter rock samples during the process of establishing bound water are shown below. Figures 2-5 As shown;

[0038] Unload the rock sample holder pressure in the order of displacement pressure, back pressure, and confining pressure, remove the full-diameter rock sample, and remove the microcrystalline wax from the central channel of the rock sample.

[0039] Step 4: Evenly spread quartz sand proppant on both ends of the full-diameter rock sample. Place a sealing plug at the outlet end of the rock sample holder to seal the outlet end. Load the sand-spread rock sample into the core holder and assemble it along the length L to complete the physical model of the volumetric fracturing horizontal well.

[0040] The size of the quartz sand proppant is determined based on the actual size of the quartz sand used in the fracturing process at the mine. Since 40 / 70 mesh quartz sand was used in the fracturing process of well A, 40 / 70 mesh quartz sand was selected in this experiment to reproduce the real conditions at the mine.

[0041] In the physical model of the volumetric fracturing horizontal well, the through-hole simulates the wellbore of the volumetric fracturing horizontal well, and the proppant-embedded end face of the full-diameter rock sample simulates the hydraulically fractured fracture. The number of rock samples used is determined according to the length of the rock sample holder. At least two full-diameter rock samples are required to complete the physical model of the volumetric fracturing horizontal well. In this example, four full-diameter rock samples, A-1, A-2, A-3, and A-4, are selected for combination. The schematic diagram of the model is shown below. Figure 5 As shown.

[0042] Step 5: Confirm the outlet end of the rock sample holder is sealed, apply confining pressure to the rock sample holder, then pump heavy water into the model from the inlet end of the rock sample holder, and apply the pumped heavy water pressure to the set value. Then close the valve at the rock sample inlet end to simulate the well shut-in process. Measure the NMR T2 spectrum curve of the volumetric fracturing horizontal well physical model every 12 hours. At 126 hours, the NMR T2 curves overlap, indicating the well shut-in process is complete. The NMR T2 spectrum curves of four full-diameter rock samples before and after simulating the well shut-in process are shown below. Figures 7-11 As shown;

[0043] The set value of the pumped heavy water pressure is determined based on the actual formation pressure after volumetric fracturing in the mine. The actual formation pressure after fracturing in well A is 14MPa. Therefore, in this example, the pumped heavy water pressure is set to 14MPa to restore the real conditions of the mine. The confining pressure needs to be set to 19MPa.

[0044] The inlet end of the rock sample holder needs to adopt a dual-channel design, with the fluid inlet channel and the fluid outlet channel being separate from each other.

[0045] Step Six: Set the back pressure at the inlet and outlet of the rock sample holder to the set value, open the valve at the inlet and outlet of the rock sample holder, simulate the flowback production process after fracturing and shutting down the well, and record the water production q2 and oil production q3 at the inlet and outlet. Measure the nuclear magnetic resonance (NMR) T2 spectrum curve of the volumetric fracturing horizontal well physical model every 12 hours. When the flowback production process reaches 96 hours, the NMR T2 curves coincide, and the flowback production process ends. The NMR T2 spectrum curves of the four full-diameter rock samples before and after the flowback production process are shown below. Figures 11-14 As shown;

[0046] The back pressure at the inlet of the rock sample holder is determined based on the actual bottom pressure of the wellbore during the flowback production process after fracturing and shutting down the well in the mine. The bottom pressure of well A during the flowback mining process is 8 MPa. Therefore, the back pressure in this example is set to 8 MPa to restore the actual conditions of the mine.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An integrated physical simulation method for "suffocation-discharge-production" in a horizontal well with volumetric fracturing in a shale oil reservoir, comprising the following steps: Step 1: Drill full-diameter plunger rock samples from the shale oil reservoir and complete the rock sample pretreatment; Step 2: Based on the rock sample that has been pretreated in Step 1, seal the through-holes with wax, then vacuum and pressurize with saturated heavy water; Step 3: Based on the saturated heavy water rock sample obtained in Step 2, use formation degassed crude oil to displace the saturated heavy water rock sample until the bound water state is reached, and remove the wax seal. Step 4: Based on the rock sample that has reached the bound water state in Step 3, quartz sand is laid on its end face, the rock samples are spliced ​​together to form a physical model of a volumetric fracturing horizontal well, and a rock sample holder is installed. Step 5: Based on Step 4, after pumping heavy water and pressurizing it into the inlet of the rock sample holder, seal the inlet of the rock sample holder to simulate the well shut-in process after fracturing; Step Six: After simulating the well blockage process achieved in Step Five, open the inlet end of the rock sample holder to simulate the post-fracturing flowback production process.

2. The integrated physical simulation method for "smothering-draining-production" in a shale oil reservoir volumetric fracturing horizontal well according to claim 1, characterized in that, The specific steps of step one are as follows: Full-diameter plunger rock samples with a length L of 15cm and a diameter d of 10cm were drilled from the shale oil reservoir. After washing and drying, the basic physical properties of the rock samples, such as mass m, permeability k, and porosity φ, were measured. The heat-shrinkable sleeve is wrapped around the entire diameter of the rock sample and heated to ensure that the sleeve tightly wraps around the sample. A 2.5cm drill bit was selected and drilled through the rock sample from the center point of the full-diameter end face along the length L direction to obtain a through-hole with a length L' of 15cm and a diameter d' of 2.5cm. The wellbore of the horizontal well was simulated by volumetric fracturing. Rock particles inside the hole were removed to complete the rock sample pretreatment.

3. The integrated physical simulation method for "smothering-draining-production" in a shale oil reservoir volumetric fracturing horizontal well according to claim 1 or 2, characterized in that, The specific steps of step two are as follows: The full-diameter rock sample was placed upright with the bottom end tightly attached to the iron sheet. Solid microcrystalline wax was heated and melted, and then poured into the channel from the top until the channel was completely filled. After the microcrystalline wax had completely cooled and solidified, the bottom iron sheet was removed, and both ends of the full-diameter rock sample were polished to make the end surfaces smooth and flat without any wax protrusions. After the rock sample was sealed with wax, it was placed in a pressure vessel and evacuated for 5 hours. Then, the pressure vessel was filled with heavy water and the pressure inside the pressure vessel was increased to 25 MPa. The pressure was maintained at 25 MPa for 72 hours. The pressure inside the pressure vessel was then released, and the full-diameter rock sample sealed with wax and saturated with heavy water was taken out.

4. The integrated physical simulation method for "smothering-draining-production" in a shale oil reservoir volumetric fracturing horizontal well according to claim 1 or 2, characterized in that, The specific steps of step three are as follows: A full-diameter rock sample sealed with wax and saturated with heavy water was placed in a rock sample holder. The holder was set to a confining pressure of 7.5 MPa, a back pressure of 2 MPa at the outlet end of the holder, and a displacement pressure of 5 MPa for the formation degassed crude oil at the inlet end of the holder. The heavy water was displaced by the formation degassed crude oil. The water production at the outlet end and the liquid output of the displacement pump were recorded. The nuclear magnetic resonance T2 spectrum curve of the rock sample was measured every 24 hours until the nuclear magnetic resonance T2 spectrum curves of two consecutive samples overlapped. Unload the rock sample holder pressure in the order of displacement pressure, back pressure, and confining pressure, remove the full-diameter rock sample, and remove the microcrystalline wax from the central channel of the rock sample.

5. The integrated physical simulation method for "smothering-draining-production" in a shale oil reservoir volumetric fracturing horizontal well according to claim 1 or 2, characterized in that, The specific steps of step four are as follows: Quartz sand proppant is spread on both ends of the full-diameter rock sample. A sealing plug is placed at the outlet end of the rock sample holder to seal the outlet end. The rock sample with sand is then loaded into the core holder to complete the physical model of the volumetric fracturing horizontal well. In the physical model of the volumetric fracturing horizontal well, the through-hole simulates the wellbore of the volumetric fracturing horizontal well, and the sand-laying end face of the full-diameter rock sample simulates the hydraulic fracturing fracture embedded with proppant. The number of rock samples used is determined according to the length of the rock sample holder. Two full-diameter rock samples can be spliced ​​together along the length L direction to complete the physical model of the volumetric fracturing horizontal well.

6. The integrated physical simulation method for "smothering-draining-production" in a shale oil reservoir volumetric fracturing horizontal well according to claim 1 or 2, characterized in that, The specific steps of step five are as follows: Confirm that the outlet end of the rock sample holder is closed, and apply confining pressure to the rock sample holder; pump heavy water into the model from the inlet end of the rock sample holder and apply the pumped heavy water pressure to the set value; close the valve at the inlet end of the rock sample holder, simulate the well suffocation process after volumetric fracturing, and measure the nuclear magnetic resonance T2 spectrum curve of the volumetric fracturing horizontal well physical model every 2 hours until the nuclear magnetic resonance T2 curves of two consecutive times coincide; The confining pressure is 5 MPa higher than the pumped heavy water pressure. The rock sample holder has a dual-channel inlet, which separates the pumped fluid channel and the fluid output channel.

7. The integrated physical simulation method for "smothering-draining-production" in a shale oil reservoir volumetric fracturing horizontal well according to claim 1 or 2, characterized in that, The specific steps of step six are as follows: Set the back pressure at the inlet and outlet of the rock sample holder to the set value, open the valve at the inlet and outlet of the rock sample holder, simulate the backflow production process after fracturing and shutting down the well, record the water production and oil production at the inlet and outlet, and measure the nuclear magnetic resonance T2 spectrum curve of the volumetric fracturing horizontal well physical model every 2 hours until the nuclear magnetic resonance T2 curves of the two consecutive times coincide. The back pressure at the inlet of the rock sample holder is determined based on the actual bottom flow pressure during the backflow production process after fracturing and shutting down the well in the mine, so as to restore the real conditions of the mine.

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