Refracturing method for low-permeability reservoir high-water-content horizontal well

Abstract

The invention discloses a refracturing method for a low-permeability reservoir high-water-content horizontal well, which comprises the following steps of: performing refracturing seam distribution design on the high-water-content horizontal well, and determining a high-water-yield seam of the high-water-content horizontal well in a target block; the safety distance S between the high-yield water crack and the adjacent fracturing crack is determined; the crack distribution design is carried out according to the principle that the distance between the high-yield water crack and the adjacent fracturing crack in the shaft direction is larger than the safety distance S; the method for determining the safe distance S comprises the steps that the predicted extension direction of the high-yield water crack is judged according to the maximum horizontal ground stress direction of the target block, and the safe distance S is determined based on the included angle alpha between the extension direction and a shaft; the problem that water logging is easily caused during refracturing construction of an existing low-permeability reservoir high-water-content horizontal well is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil production engineering, and in particular to a repeated fracturing process for a horizontal well with high water content in a low permeability reservoir. Background Art

[0002] Currently, repeated fracturing is carried out on horizontal wells with high water content in low permeability reservoirs. When repeated fracturing is carried out after water plugging in the horizontal wells, if the repeated fracturing cracks are too close to the water plugging cracks, the water plugging cracks may fail due to matrix seepage, resulting in flooding. Therefore, it is necessary to develop corresponding repeated fracturing construction methods for horizontal wells with high water content in low permeability reservoirs. Summary of the invention

[0003] In view of this, the present disclosure provides a method for repeated fracturing of horizontal wells with high water content in low permeability reservoirs, which solves the problem that repeated fracturing of horizontal wells with high water content in existing low permeability reservoirs is prone to flooding.

[0004] To achieve the above-mentioned purpose of the invention, the method for repeated fracturing of a high-water-content horizontal well in a low-permeability reservoir comprises designing repeated fracturing seam arrangement for the high-water-content horizontal well, wherein: Identify high-water-yielding fractures in high-water-cut horizontal wells within the target area; Determine a safe distance S between the high-water-yield fracture and an adjacent hydraulic fracture; The seam arrangement design is performed according to the principle that the distance between the high water yield fracture and the adjacent hydraulic fracture along the wellbore direction should be greater than the safety distance S; The method for determining the safety distance S comprises: According to the direction of the maximum horizontal ground stress in the target block, the expected extension direction of the high-water-yield fracture is determined, and the safety distance S is determined based on the angle α between the extension direction and the wellbore.

[0005] In the present disclosure and some possible embodiments, the maximum vertical distance between two artificial fractures where inter-stage crossflow occurs during the previous horizontal well staged fracturing construction in the target block is used as a reference value D for the safety distance between the high-yield water fracture and the adjacent fracturing fracture. If there is no relevant reference value, the reference value D is 30m. When the angle α=90°, S=D, when 0°﹤α﹤90°, S=D / sinα, and when 90°﹤α﹤180°, S=D / sin(α-90°).

[0006] In the present disclosure and some possible embodiments, the method of seam design includes: When the length of the sandstone layer section on both sides or one side of the high-water-yield fracture is greater than the safety distance S, seams are designed in the sandstone layer section; when the length of the sandstone layer section is less than or equal to the safety distance S, seams are not designed during repeated fracturing in the sandstone layer section; The lengths of the sandstone segments on both sides of the high-yield water fracture are less than or equal to the safety distance S, and the sandstone segment is adjacent to the mudstone segment. When the length of the mudstone segment on both sides or on one side is ≥20m, the seams are designed at the starting position of the other sandstone segment adjacent to the mudstone segment; when the length of the mudstone segment on both sides or on one side is <20m, the length S1 of the sandstone segment on the corresponding side and the length S2 of the mudstone segment are obtained, and the other end of the mudstone segment is taken as the starting point, and S3=S-S1-S2×1.5 is taken as the length, and the seams are designed in the other sandstone segment adjacent to the mudstone segment.

[0007] In the present disclosure and some possible embodiments, the length of the sandstone layer sections on both sides or one side of the high-water-yield fracture is greater than or equal to two of the safety distances S, and the adjacent repeated fracturing fractures in the sandstone layer cannot use the intra-fracture temporary plugging and diversion process.

[0008] In the present disclosure and possible embodiments, the high-water-yield fractures are determined by geological analysis methods; The geological analysis method is to obtain the location of high-yield water fractures through the relationship between sedimentary phase belts and horizontal wells and adjacent water injection wells.

[0009] In the present disclosure and possible embodiments, the high water production fracture is determined by a field testing method; The field testing method is to insert a horizontal well segmented productivity measurement and control tool into the target well, use a cable to transmit signals, obtain the downhole liquid production and water content data of each section through a ground direct reading terminal, and obtain the water production of each section through the liquid production and water content to determine the location of the high water production fracture.

[0010] In the present disclosure and some possible embodiments, when performing repeated fracturing operations, water plugging operations are performed on the high-water-yield fractures, and whether the water plugging is effective is judged based on the production effect after the operation. If the water plugging is effective, repeated fracturing operations are performed on the well. If the water plugging is not effective, the water plugging operation is performed again until the water plugging is effective.

[0011] In the present disclosure and some possible embodiments, when performing fracturing construction on a fracturing crack adjacent to the high water content crack, it is determined whether the fracturing crack is in communication with the high water content crack. If so, the safety distance S is corrected.

[0012] The method of the present invention determines a reasonable safety distance S between the artificial fracture and the adjacent repeated fracturing fracture for high-yield water fractures in combination with the direction of the wellbore, guides the repeated fracturing target well to select the location of the fracture according to the safety distance S, and then effectively plugs the target well first and then performs repeated fracturing, thereby improving the single well production of high-water-content horizontal wells in low-permeability reservoirs, combining water plugging and repeated fracturing in old horizontal wells with high water content, improving the water injection development effect of low-permeability horizontal wells, and solving the problem that repeated fracturing construction of high-water-content horizontal wells in existing low-permeability reservoirs is prone to flooding. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which: Figure 1 It is a schematic diagram of the design of the seam layout of the sandstone layer section where the high-yield water fractures are located when the length of the sandstone layer section is greater than the safety distance S of the present invention; Figure 2 It is a schematic diagram of the design of the seam layout of the sandstone layer section where the high-yield water fractures are located when the length of the sandstone layer section is less than or equal to the safety distance S of the present invention; Figure 3 The schematic diagram of the design of the seam layout is that the lengths of the sandstone layers on the left and right sides of the high-yield water fracture of the present invention are both less than or equal to the safety distance S, and the other ends of the mudstone layers on both sides are adjacent to the sandstone layers; Figure 4 Schematic diagram of high-water-yield fractures and sandstone layers of horizontal well A in block Z of Example 1 of the present disclosure; Figure 5 It is a schematic diagram of fracturing arrangement of a target well for repeated fracturing according to Example 1 of the present disclosure. Implementation

[0014] The present disclosure is described below based on embodiments, but it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, some specific details are described in detail. However, for the parts that are not described in detail, those skilled in the art can also fully understand the present disclosure.

[0015] In addition, those skilled in the art should understand that the drawings are only provided to illustrate the purpose, features and advantages of the present disclosure, and the drawings are not actually drawn to scale.

[0016] At the same time, unless the context clearly requires otherwise, the words "include", "comprises" and similar words throughout the specification and claims should be interpreted as inclusive rather than exclusive or exhaustive; that is, the meaning is "including but not limited to".

[0017] The method for repeated fracturing of horizontal wells with high water content in low permeability reservoirs adopted in the embodiment of the present disclosure is shown in the accompanying drawings, and the specific steps are as follows: Step 1: Identify high-water-yield fractures in high-water-cut horizontal wells in the target area: Specifically, high-water-yield fractures in high-water-content horizontal wells in the target block are determined through geological analysis methods or field testing methods. The geological analysis method is to comprehensively judge and analyze the location of high-water-yield fractures through the sedimentary facies belts and the relationship between horizontal wells and adjacent water injection wells; the field testing method is to insert a horizontal well segmented production capacity measurement and control tool into the target well, use cables to transmit signals, obtain the production capacity status of each section through the ground direct reading terminal, measure the downhole liquid production, water content and other data, directly determine the water production of each section, and determine high-water-yield fractures.

[0018] Step 2: Determine the reasonable safety distance S between high-water-yield fractures and adjacent hydraulic fractures: First, the expected extension direction of artificial fractures in high-water-content horizontal wells is determined based on the maximum horizontal geostress direction of the target block; if the target block has only been tested for geostress direction, the extension direction of artificial fractures is always consistent with the direction of maximum horizontal principal stress, so the direction of maximum horizontal principal stress is used as the expected extension direction of artificial fractures in this well; if the wells in this block have been monitored by fracturing microseismic monitoring or other monitoring, the monitored extension direction of artificial fractures is used as the expected extension direction of high-water-yield fractures in this well. ; Then, according to the maximum vertical distance between two artificial fractures with inter-stage crossflow during the previous horizontal well staged fracturing construction in the target block, the safety distance reference value D between the high-yield water fracture and the adjacent fracturing fracture is taken as the reference value D. If there is no relevant reference value, the reference value D is taken as 30m; Finally, based on the angle α between the extension direction and the wellbore, the reasonable safety distance S between the high-yield water fracture and the adjacent hydraulic fracture is determined. Specifically, when the angle α=90°, S=D; when 0°﹤α﹤90°, S=D / sinα; when 90°﹤α﹤180°, S=D / sin(α-90°).

[0019] Step 3: Design repeated fracturing layout for the high water-cut horizontal well: The principle of repeated fracturing layout design for this high water-content horizontal well is: high water-yielding fractures need to be plugged, and other fractures are repeated fracturing. The distance between repeated fracturing fractures and high water-yielding fractures along the wellbore direction must be greater than the safety distance S to ensure that repeated fracturing fractures will not communicate with high water-yielding fractures. The layout design is carried out according to the following conditions: 1. If the lengths of the sandstone sections on both sides of the high-yield water fracture are greater than the safety distance S, such as Figure 1 As shown, the third fracture is a high-water-yield fracture. The sandstone layers on the left and right sides of the high-water-yield fracture are designed with fractures, and the new fractures obtained by repeated fracturing and pressure replenishment are the second and fourth fractures respectively. If the length of only one side of the sandstone layer of the high-yield water fracture is greater than the safety distance S, such as Figure 2 As shown, the second crack is a high-water-yield crack. The length of the sandstone layer section on the right side of the high-water-yield crack is greater than the safety distance S. Therefore, the cracks are designed only in the sandstone layer section on the right side. The new crack obtained by repeated fracturing and pressure replenishment is the third crack in the figure, and the same is true for the left side.

[0020] 2. When the length of the sandstone layer section on the left and right sides or one side of the high-water-yield fracture is less than or equal to the safety distance S, no seam layout is designed when repeated fracturing is performed in the sandstone layer section; Figure 2 As shown in the figure, the length of the sandstone layer section on the left side of the high-water-yield fracture is less than the safety distance S, so no joints are designed on the left side.

[0021] 3. The length of the sandstone layer sections on both sides of the high-yield water fracture is less than or equal to the safety distance S, and the sandstone layer section is adjacent to the mudstone layer section. If the length of the mudstone layer section is ≥20m, Figure 3 As shown in the figure, the third fracture is a high-water-yield fracture. The mudstone layer section on the left side of the high-water-yield fracture is ≥ 20m. Then, the fractures are designed at the beginning of another sandstone layer section adjacent to the mudstone layer section. The new fracture obtained by repeated fracturing and pressure replenishment is the second fracture in the figure. If the length of the mudstone layer is less than 20m, Figure 3 As shown, the mudstone segment on the right side of the high-yield water fracture 3 is less than 20m. It is necessary to obtain the length S1 and the length S2 of the sandstone segment respectively. Then, taking the other end of the mudstone segment as the starting point and S3=S-S1-S2×1.5 as the length, design the fracture layout in another sandstone segment adjacent to the mudstone segment. The new fracture obtained by repeated fracturing and pressure replenishment is the fourth fracture in the figure.

[0022] 4. If the high-water-yield fracture is located in a large sandstone layer, and the length of the large sandstone layer is greater than or equal to two safety distances S, when designing the repeated fracturing, the adjacent repeated fracturing fractures in the sandstone layer cannot use the temporary plugging and diversion technology within the fracture to prevent the high-water-yield fractures from communicating through diversion.

[0023] Step 4: Water plugging for high water production cracks: If the water plugging operation is performed on the high-water-yield fractures and the water plugging is not successful, the next step of repeated fracturing may cause the water production and water content to further increase, so the prerequisite for repeated fracturing is to effectively plug the high-water-yield fractures. Specifically, according to the conventional technology in this field, a water plugging agent is injected into the high-water-yield fractures of the repeated fracturing target well to plug the layer section, and the water plugging is judged based on the production effect after the operation. If the water plugging is effective, the well is repeated for fracturing. If the water plugging is not effective, the water plugging operation is repeated until the water plugging is effective.

[0024] Step 5: According to the conventional technology in this field, a perforating gun string is inserted into the target horizontal well for repeated fracturing, and the new seam position that needs to be re-pressurized is perforated. The perforating string is pulled out, and the perforated well section and the packer setting position are scraped and cleared.

[0025] Step 6: According to the conventional technology in this field, the double-seal single-clamp fracturing string is lowered, the fracturing wellhead is installed, the fracturing manifold is connected, and the surface pipeline and the gate are pressure tested. The pipeline is qualified if there is no puncture, leakage or seepage.

[0026] Step 7: According to the conventional technology in this field, the horizontal well is designed to be repeatedly fractured and the pipe string is lifted step by step to complete the repeated fracture construction in sequence, and the water blocking fracture is not fractured.

[0027] During the fracturing construction process, when performing fracturing construction on adjacent cracks of high water content cracks, it is necessary to pay attention to whether the fracturing cracks are connected with the high water content cracks, which is mainly manifested in the following two characteristics: First, after communicating with the high water production cracks, the tubing pressure will be significantly reduced rapidly; second, since the fracturing construction is dragged from the bottom of the well upward step by step, the casing pressure can be used to determine whether the lower fracturing layer section is connected with the upper high water production cracks. If it is found during the construction process that the designed safety distance S is still insufficient to effectively isolate the high water content cracks from the adjacent repeated fracturing cracks, the safety distance S value needs to be further corrected, and the subsequent repeated fracturing seam layout design of such wells should be carried out according to the corrected safety distance.

[0028] Step 8: After all the designed target layers are constructed, the fracturing string is removed from the well and the pump is lowered to start production. Example

[0029] The low permeability reservoir horizontal well Z block in the periphery of Daqing has a reservoir permeability of 30mD-100mD. There are 15 horizontal wells in the block, including A. Currently, 11 wells have a water content of more than 90%, and the production effect is poor. Among them, A horizontal well has been fracturing and put into production for 7 years, and currently produces 27m of water per day. 3 , daily oil production 0.8m 3 , water content 97.1%.

[0030] The A horizontal well with high water content adopts the repeated fracturing process of the present invention, and the specific steps are as follows: Step 1: Run the horizontal well segmented productivity measurement and control tool into horizontal well A, and determine through testing that the high-yield water fractures in horizontal well A are Figure 4 The second crack.

[0031] Step 2: The extension direction of artificial fractures in the Z block is NE12°-NE26°, with an average of NE18°. It is determined that the expected extension direction of artificial fractures in horizontal wells is NE18°. The previous horizontal well fracturing construction data of the Z block show that the maximum vertical distance between two artificial fractures in the Z block without crossflow is 25m, that is, the reference value of the safety distance D is 25m. Combined with the angle α between the wellbore and the fracture extension direction of 72°, the reasonable safety distance S=25 / sin72°=26.3m between high-yield water fractures and adjacent fracturing fractures is determined.

[0032] Step 3: Repeated fracturing layout design for horizontal well A. There are large sections of sandstone on both sides of the original high-yield fractures in horizontal well A that have not been transformed. During repeated fracturing, pressure supplementation is required to achieve full transformation of the horizontal well. Taking the 26.3m fracture distance as a reference, the repeated fracturing layout is designed, such as Figure 5 The distance between the second crack and the third crack is 27m, and the distance between the third crack and the fourth crack is 27m.

[0033] Step 4: Water plugging operation was carried out in the high-yield water fracture of horizontal well A. Water plugging agent was injected into the second fracture. After plugging, the daily water production of the whole well was 18m 3 , daily oil production 3.5m 3 , the water content dropped from 97.1% to 83.7%, and it was judged that the water plugging was effective.

[0034] Step 5: Insert the perforating gun string into the A horizontal well, perforate the second and fourth fractures of the new pressure-compensated fractures, pull out the perforating string, and scrape the perforated well section and the packer setting position to clear the well.

[0035] Step 6: Lower the double-seal single-clamp fracturing string, install the fracturing wellhead, connect the fracturing manifold, and conduct pressure test on the surface pipeline and gate. The pipeline is qualified if there is no puncture, leakage or seepage.

[0036] Step 7: Repeat fracturing construction is carried out on horizontal well A. The double-seal single-clamp fracturing process string is used. The string is lifted up step by step to complete the repeated fracturing section construction in sequence. The third crack is not fractured.

[0037] Step 8: After the construction of the fifth crack is completed, the fracturing string in the well is removed and the pump is lowered to start production.

[0038] The above-described embodiments are only embodiments of the present disclosure, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the present disclosure. It should be noted that, for a person of ordinary skill in the art, without departing from the concept of the present disclosure, several variations, equivalent substitutions, improvements, etc. may be made, all of which fall within the scope of protection of the present disclosure. Therefore, the scope of protection of the present disclosure shall be subject to the attached claims.

Claims

1. A method for repeated fracturing of a high water-content horizontal well in a low permeability reservoir, comprising designing a repeated fracturing seam arrangement for the high water-content horizontal well, characterized in that: Identify high-water-yielding fractures in high-water-cut horizontal wells within the target area; Determine a safe distance S between the high-water-yield fracture and an adjacent hydraulic fracture; The seam arrangement design is performed according to the principle that the distance between the high-water-yield fracture and the adjacent hydraulic fracture along the wellbore direction is greater than the safety distance S; The method for determining the safety distance S comprises: According to the direction of the maximum horizontal ground stress in the target block, the expected extension direction of the high-water-yield fracture is determined, and the safety distance S is determined based on the angle α between the extension direction and the wellbore.

2. The repeated fracturing method for horizontal wells with high water content in low permeability reservoirs according to claim 1, characterized in that: The maximum vertical distance between two artificial fractures where inter-stage crossflow occurred during the previous horizontal well staged fracturing construction in the target block is used as a reference value D for the safe distance between the high-water-yield fracture and the adjacent fracturing fracture. If there is no relevant reference value, the reference value D is 30m; When the angle α=90°, S=D, when 0°﹤α﹤90°, S=D / sinα, and when 90°﹤α﹤180°, S=D / sin(α-90°).

3. The repeated fracturing method for high water content horizontal wells in low permeability reservoirs according to claim 2, characterized in that: The method for fabric seam design comprises: When the length of the sandstone layer section on both sides or one side of the high-water-yield fracture is greater than the safety distance S, seams are designed in the sandstone layer section; when the length of the sandstone layer section is less than or equal to the safety distance S, seams are not designed during repeated fracturing in the sandstone layer section; The lengths of the sandstone segments on both sides of the high-yield water fracture are less than or equal to the safety distance S, and the sandstone segment is adjacent to the mudstone segment. When the length of the mudstone segment on both sides or on one side is ≥20m, the seams are designed at the starting position of the other sandstone segment adjacent to the mudstone segment; when the length of the mudstone segment on both sides or on one side is <20m, the length S1 of the sandstone segment on the corresponding side and the length S2 of the mudstone segment are obtained, and the other end of the mudstone segment is taken as the starting point, and S3=S-S1-S2×1.5 is taken as the length, and the seams are designed in the other sandstone segment adjacent to the mudstone segment.

4. The repeated fracturing method for high water content horizontal wells in low permeability reservoirs according to claim 3, characterized in that: The length of the sandstone layer sections on both sides or one side of the high-water-yield fracture is greater than or equal to the two safety distances S, and the adjacent repeated fracturing fractures in the sandstone layer cannot adopt the in-fracture temporary plugging and diversion technology.

5. The repeated fracturing method for a horizontal well in a low permeability reservoir with high water content according to any one of claims 1 to 4, characterized in that: Determine the high-water-yield fractures by geological analysis methods; The geological analysis method is to obtain the location of high-yield water fractures through the relationship between sedimentary phase belts and horizontal wells and adjacent water injection wells.

6. The repeated fracturing method for a horizontal well in a low permeability reservoir with high water content according to any one of claims 1 to 4, characterized in that: Determining the high water production fractures by a field testing method; The field testing method is to insert a horizontal well segmented productivity measurement and control tool into the target well, use a cable to transmit signals, obtain the downhole liquid production and water content data of each section through a ground direct reading terminal, and obtain the water production of each section through the liquid production and water content to determine the location of the high water production fracture.

7. The repeated fracturing method for a horizontal well in a low permeability reservoir with high water content according to any one of claims 1 to 4, characterized in that: When performing repeated fracturing operations, water plugging operations are performed on the high-water-yield fractures, and whether the water plugging is effective is judged based on the production effect after the operation. If the water plugging is effective, repeated fracturing operations are performed on the well. If the water plugging is not effective, the water plugging operation is performed again until the water plugging is effective.

8. The repeated fracturing method for high water content horizontal wells in low permeability reservoirs according to claim 7, characterized in that: When performing fracturing construction on the fracturing crack adjacent to the high water content crack, it is determined whether the fracturing crack is in communication with the high water content crack. If so, the safety distance S is corrected.

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