A spatial three-dimensional rough and tortuous crack temporary plugging agent formula optimization method

Abstract

The application belongs to the technical field of temporary plugging agents, and particularly relates to a space three-dimensional rough and tortuous crack temporary plugging agent formula optimization method. The method comprises the following steps: preparing a homogeneous cubic outcrop rock sample, and performing wellbore completion; controlling the three-way stress value, so that the rock sample generates a space three-dimensional hydraulic fracture; knocking the rock sample along the crack path by using a rubber hammer with a rubber pad; bonding steel balls with different particle sizes around the crack surface by using epoxy resin, and controlling the crack opening degree; expanding the pipeline inner diameter, pumping temporary plugging agents with different formulas to plug the cracks; setting the maximum pumping pressure, recording the pumping pressure and fluid pumping volume, observing the temporary plugging agent laying form on the three-dimensional crack surface, and judging whether the temporary plugging agent formula can be used for in-crack plugging construction. The method solves the problems that the existing method cannot completely simulate the temporary plugging and fracturing process and cannot consider the influence of the space three-dimensional crack form, and ensures that the optimized temporary plugging agent formula obtains more reliable temporary plugging effect.

Description

Technical Field

[0001] This invention belongs to the field of temporary plugging agent technology, specifically relating to a method for optimizing the formulation of a temporary plugging agent for three-dimensional rough and tortuous cracks. Background Technology

[0002] Hydraulic fracturing, which creates a network of intersecting fractures to "break up" the reservoir, is a key method for the profitable development of oil and gas resources. In-fracture plugging can effectively block fluid flow within the fractures, significantly increasing net pressure. In-fracture temporary plugging and diversion fracturing technology, which primarily uses in-fracture plugging, can significantly activate natural weak surfaces and improve the overall reservoir stimulation effect. The key to achieving in-fracture temporary plugging and diversion lies in optimizing the plugging agent formulation to ensure effective sealing within the hydraulic fractures and inhibit the propagation of the main fracture.

[0003] Currently, the preferred methods for temporary plugging within fractures mainly include trench plugging tests, fracturing and fracture creation plugging tests, 3D-printed fracture model plugging tests, and large-scale hydraulic fracturing plugging tests. Trench plugging tests cannot reflect the influence of the actual fracture wall morphology, and the fracture model size is too small. In fracturing and fracture creation plugging tests, the pipeline is directly connected to the fracture opening, which cannot simulate the dynamic process of the plugging agent changing direction and migrating from the wellbore into the fracture, and the wedge-shaped fracture opening design ignores the influence of the throttling effect at the fracture opening. Although 3D-printed fracture models can reconstruct the rough surface of the fracture, the fracture surface is not a three-dimensional structure, and the plugging agent flows in a single direction within the fracture. Large-scale hydraulic fracturing plugging tests can simulate the entire temporary plugging fracturing process, including injecting fracturing fluid to generate hydraulic fractures, pumping in temporary plugging agent to seal the fracture, and pumping in fracturing fluid to generate new fractures. In addition, this experimental process can generate three-dimensional fracture morphology and can consider the influence of fracture opening direction change and throttling effect. However, in this type of experiment, the temporary plugging agent mainly accumulates inside the wellbore and is difficult to migrate into the fracture, making it impossible to explore the migration and sealing patterns of the temporary plugging agent within the fracture. Summary of the Invention

[0004] To overcome the above technical problems, this invention provides a method for optimizing the formulation of a temporary plugging agent for three-dimensional rough and tortuous fractures. This method solves the problems that existing methods cannot fully simulate the temporary plugging fracturing process and cannot consider the influence of three-dimensional fracture morphology, ensuring that the optimized temporary plugging agent formulation achieves a more reliable plugging effect.

[0005] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0006] A method for optimizing the formulation of a temporary plugging agent for three-dimensional rough and tortuous cracks includes the following steps:

[0007] Step 1: Prepare and select homogeneous cubic outcrop rock samples for well completion;

[0008] Step 2: Control the magnitude of the triaxial stress value to induce hydraulic fractures in the rock sample in a three-dimensional spatial shape;

[0009] Step 3: Use a rubber mallet with a rubber pad to tap the rock sample along the crack path;

[0010] Step 4: Use epoxy resin to bond steel balls of different sizes around the crack surface to control the crack opening.

[0011] Step 5: Enlarge the inner diameter of the pipeline and pump in temporary plugging agents with different formulations to seal the cracks;

[0012] Step 6: Set the maximum pumping pressure, record the pumping pressure and fluid pumping volume, observe the placement pattern of the temporary plugging agent on the three-dimensional fracture surface, and determine whether the temporary plugging agent formulation can be used for downhole fracture sealing construction.

[0013] Preferably, in step 1, the homogeneous cubic outcrop rock sample has a side length of 300-400 mm.

[0014] Preferably, in step 1, the inner diameter of the wellbore completion is 45-55 mm.

[0015] Preferably, in step 1, a 300-400 mm cubic outcrop rock sample is prepared by wire cutting. The outcrop rock sample does not contain natural cracks or large pores and does not exhibit stratification, thus ensuring the homogeneity of the outcrop rock sample.

[0016] In step 1, a cylindrical hole with a length of 200-250 mm and an inner diameter of 45-55 mm is drilled vertically on one side of the outcrop rock sample using drilling equipment. A steel pipe with a length of 125-175 mm, an inner diameter of 15-18 mm, and an outer diameter of 42-52 mm is fixed in the open hole with epoxy resin, and the reserved length of the open hole section is 75 mm.

[0017] Preferably, in step 2, the wellbore direction is along the X direction, and the two directions perpendicular to the wellbore are the Y and Z directions. When a transverse cut perpendicular to the wellbore is required, the stress in the X direction is controlled to be 4 MPa greater than the stress in the Y and Z directions. When a vertical cut along the wellbore is required, the stress in the Y or Z direction is controlled to be 4 MPa greater than the stress in the X direction. When an inclined cut is required, the stress in the X direction is controlled to be less than 4 MPa greater than the smaller stress in the Y and Z directions.

[0018] Preferably, in step 4, the selected steel balls have diameters of 1mm, 2mm, 3mm, 4mm, 5mm, 6mm and 7mm, and high-strength epoxy resin is used to evenly lay the steel balls around the crack.

[0019] Preferably, in step 5, a high-pressure rubber pipeline is used to connect the rock sample clamping cavity and the intermediate container. The intermediate container is filled with fracturing fluid containing temporary plugging agents of different formulations. Clean water is pumped in using a constant flow pump. The clean water pushes the piston in the intermediate container, pumping the fracturing fluid containing temporary plugging agents into the rock sample to seal the cracks.

[0020] Preferably, in step 5, the inner diameter of the pipeline is increased to 15-18 mm.

[0021] Preferably, in step 6, the maximum pumping pressure is set to 3-5 MPa, the constant flow pumping speed is 30-60 ml / min, the pump is stopped when the pumping pressure reaches 3-5 MPa, the fracture surface is opened, and when an effective bridging is formed in the fracture, and the pumping time to reach 3-5 MPa is less than 8000 s, the temporary plugging agent formula can be used for downhole fracture sealing construction.

[0022] Compared with the prior art, the technical advantages of the present invention are as follows:

[0023] The method described in this invention can reflect the actual fracture morphology, and the optimized formula provides a more reliable plugging effect. The method described in this invention can better control fracture aperture, simulate different underground scenarios, and help establish a library of temporary plugging solutions. Based on the optimized temporary plugging agent formula obtained in this invention, the success rate of in-situ temporary plugging fracturing can be significantly improved, reservoir stimulation volume can be increased, and single-well production can be increased. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the optimization of a spatial three-dimensional rough and tortuous crack plugging agent formulation in an embodiment of the present invention.

[0025] Figure 2 This is the arrangement of steel balls in an embodiment of the present invention.

[0026] The present invention will now be further described in conjunction with the accompanying drawings and embodiments. Detailed Implementation

[0027] The present invention will be described below through specific embodiments to make the technical solution of the present invention easier to understand and master, but the present invention is not limited thereto. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are all commercially available.

[0028] Example 1

[0029] A method for optimizing the formulation of a temporary plugging agent for three-dimensional rough and tortuous cracks, with the optimization flowchart as shown below. Figure 1 It includes the following steps:

[0030] S101: Prepare and select homogeneous 300mm×300mm×300mm outcrop rock samples for well completion with a 50mm inner diameter wellbore, specifically:

[0031] The target reservoir is a uniform dense sandstone reservoir. Homogeneous sandstone outcrops without stratification and natural fractures were selected from the reservoir, and 300mm×300mm×300mm outcrop rock samples were prepared by wire cutting.

[0032] A cylindrical hole, 200 mm long and 50 mm in inner diameter, was drilled vertically into the outcrop rock sample using drilling equipment. A steel pipe, 125 mm long, 16 mm in inner diameter, and 47 mm in outer diameter, was then fixed in the open hole with epoxy resin, with a 75 mm reserved length in the open hole section.

[0033] S102: Controls the magnitude of triaxial stress to generate a three-dimensional hydraulic fracture, specifically:

[0034] The wellbore is oriented along the X-direction, and the two directions perpendicular to the wellbore are the Y and Z directions. In this embodiment, an inclined joint is to be generated, and the stress value in the X-direction is controlled to be 3 MPa, the stress in the Y-direction is 1 MPa, and the stress in the Z-direction is 3 MPa.

[0035] S103: Use a rubber mallet with a rubber pad to tap the rock sample along the crack path, specifically:

[0036] A rubber mallet was used to repeatedly tap along the propagation path of the hydraulically induced cracks to gradually open them and prevent the formation of new cracks. This resulted in a tilted, three-dimensional, rough, and tortuous crack surface structure.

[0037] S104: Steel balls of different sizes are bonded to the crack surface with epoxy resin to control the crack opening. Specifically:

[0038] In this embodiment, steel balls with a diameter of 3mm are used. High-strength epoxy resin is used to evenly lay the steel balls around the crack to ensure that the hydraulic crack has a certain opening after pressure is applied to the crack surface. The crack opening is approximately equal to the diameter of the steel balls; therefore, the crack support opening is 3mm. Laying the steel balls around the crack also prevents them from affecting the migration of the temporary plugging agent within the crack. The method of laying the steel balls around the crack is as follows: Figure 2 As shown.

[0039] S105: Enlarge the pipeline inner diameter to 16mm, and pump in temporary plugging agents of different formulations to seal the cracks, specifically:

[0040] A high-pressure rubber hose connects the rock sample clamping chamber and the intermediate container. The intermediate container contains fracturing fluid with different formulations of temporary plugging agents. Commonly used temporary plugging agents in field fracturing include 6mm fibers and 1-8mm spherical particles, typically made of polylactic acid. A constant-flow pump injects clean water at a rate of 30mL / min. The water pushes the piston in the intermediate container, pumping the fracturing fluid containing the temporary plugging agent into the rock sample to seal the fractures.

[0041] S106: Set the maximum pumping pressure, record the pumping pressure and fluid pumping volume, and observe the placement morphology of the temporary plugging agent on the three-dimensional fracture surface, specifically:

[0042] The maximum pumping pressure was set to 3 MPa to avoid damaging the rock sample due to excessive pressure, which would prevent repeatable tests. The constant flow pump was used at a rate of 30 mL / min. The pump was stopped when the pressure reached 3 MPa, the fracture surface was opened, and the placement of the temporary plugging agent within the fracture was observed. Based on the pumping time at 3 MPa and the bridging pattern of the temporary plugging agent within the fracture, the optimal temporary plugging agent formulation for a given fracture width was determined. When effective bridging is formed within the fracture, and the pumping time to reach 3 MPa is less than 8000 s, this temporary plugging agent formulation can be used for downhole fracture sealing. Therefore, the plugging agent formulation for sealing a 3 mm three-dimensional rough tortuous fracture is: 1% fiber (polylactic acid) + 1% 1 mm particles (polylactic acid) + 1% 2 mm particles (polylactic acid). The fiber length is 6 mm.

[0043] Comparative Example 1

[0044] For this target reservoir, a conventional method was used to optimize the temporary plugging agent formulation. Downhole core samples were taken, and two fracture surfaces were prepared using a splitting method. These two fracture surfaces were then placed in a core flow device. A mixture of fiber and particles was placed at the fracture inlet, and fluid was injected using an ISCO pump. The fluid propelled the temporary plugging agent mixture, causing it to accumulate at the fracture inlet and gradually compact, forming a seal with a pressure resistance of 30 MPa. Changing the mass concentration ratio of fiber and particles showed that fracture sealing could be achieved regardless of the ratio. Considering economic efficiency, a 1% mass concentration fiber (polylactic acid) + 1% 1mm particles (polylactic acid) mixture was selected for field testing. During field operations, no significant pressure increase was observed, indicating that effective sealing was not achieved. This method uses a small-scale fracture model, failing to consider the true morphology of three-dimensional fractures, resulting in low reliability of the optimized temporary plugging agent formulation. Production results showed that the output was comparable to adjacent non-temporarily plugged wells, indicating that the temporary plugging and diversion effect was not achieved.

[0045] Application effect test

[0046] A field experiment was conducted on a horizontal well in a tight sandstone reservoir in Xinjiang. The well has a depth of 4200m, a horizontal section length of 920m, an average stimulated section length of 90m, six perforations in a single section, and a drilling flow rate of 12m³ / h. 3 / min. The average fracture width was simulated using integrated geological engineering numerical simulation software to be 3mm. The temporary plugging agent formulation optimized in Example 1 was used: 1% fiber + 1% 1mm particles + 1% 2mm particles. After construction, compared with adjacent non-plugged wells of the same construction scale, the production increased by 20%, confirming the reliability of the method established in this invention.

[0047] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A method for optimizing a formulation of a spatial three-dimensional rough and tortuous fracture temporary plugging agent, characterized in that, Includes the following steps: Step 1: Prepare homogeneous cubic outcrop rock samples for well completion; Step 2: Control the magnitude of the triaxial stress value to induce hydraulic fractures in the rock sample in a three-dimensional spatial shape; Step 3: Use a rubber mallet with a rubber pad to tap the rock sample along the crack path; Step 4: Use epoxy resin to bond steel balls of different sizes around the crack surface to control the crack opening. Step 5: Enlarge the inner diameter of the pipeline and pump in temporary plugging agents with different formulations to seal the cracks; Step 6: Set the maximum pumping pressure, record the pumping pressure and fluid pumping volume, observe the placement pattern of the temporary plugging agent on the three-dimensional fracture surface, and determine whether the temporary plugging agent formulation can be used for downhole fracture sealing construction.

2. The method of optimizing a bridging fluid formulation of claim 1, wherein, In step 1, the homogeneous cubic outcrop rock sample has a side length of 300~400mm.

3. The method of optimizing a bridging fluid formulation of claim 1, wherein, In step 1, the inner diameter of the wellbore completion is 45~55mm.

4. The method of optimizing a bridging fluid formulation of claim 1, wherein, In step 1, a 300-400 mm cubic outcrop rock sample is prepared by wire cutting. The outcrop rock sample does not contain natural cracks or large pores and does not exhibit stratification, ensuring that the outcrop rock sample is homogeneous.

5. The method of optimizing a bridging fluid formulation of claim 1, wherein, In step 1, a cylindrical hole with a length of 200-250 mm and an inner diameter of 45-55 mm is drilled vertically on one side of the outcrop rock sample using drilling equipment. A steel pipe with a length of 125-175 mm, an inner diameter of 15-18 mm, and an outer diameter of 42-52 mm is fixed in the open hole with epoxy resin, and the reserved length of the open hole section is 75 mm.

6. The method of optimizing a bridging fluid formulation of claim 1, wherein, In step 2, the wellbore is oriented along the X direction, and the two directions perpendicular to the wellbore are the Y and Z directions. When a transverse cut perpendicular to the wellbore is required, the stress in the X direction is controlled to be 4 MPa greater than the stress in the Y and Z directions. When a vertical cut is required along the wellbore, the stress in the Y or Z direction is controlled to be 4 MPa greater than the stress in the X direction. When an inclined cut is required, the stress in the X direction is controlled to be less than 4 MPa greater than the smaller stress in the Y and Z directions.

7. The method of optimizing a bridging fluid formulation of claim 1, wherein, In step 4, steel balls with diameters of 1mm, 2mm, 3mm, 4mm, 5mm, 6mm and 7mm were selected, and epoxy resin was used to evenly spread the steel balls around the crack.

8. The method of optimizing a bridging fluid formulation of claim 1, wherein, In step 5, a high-pressure rubber pipeline is used to connect the rock sample clamping cavity and the intermediate container. The intermediate container is filled with fracturing fluid containing temporary plugging agents of different formulations. Clean water is pumped in using a constant flow pump. The clean water pushes the piston in the intermediate container, pumping the fracturing fluid containing temporary plugging agents into the rock sample to seal the fractures.

9. The method for optimizing the formulation of the temporary plugging agent as described in claim 1, characterized in that, In step 5, the inner diameter of the pipeline is increased to 15-18mm.

10. The method for optimizing the formulation of the temporary plugging agent as described in claim 1, characterized in that, In step 6, the maximum pumping pressure is set to 3~5 MPa, the constant flow pumping speed is 30~60 ml / min, the pump is stopped when the pumping pressure reaches 3~5 MPa, the fracture surface is opened, and when an effective bridging is formed in the fracture, and the pumping time to reach 3~5 MPa is less than 8000 s, the temporary plugging agent formula can be used for downhole fracture sealing construction.

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