Low-permeability and tight reservoir straight-flat combined fracturing optimization design method

Abstract

The invention relates to the technical field of oil production engineering, in particular to a straight-flat combined fracturing optimization design method for a low-permeability and tight reservoir. The low-permeability and tight reservoir straight-flat combined fracturing optimization design method comprises the steps that according to block characteristics, a block transformation mode is judged; the distance between each vertical well and the horizontal well on the periphery is determined; the reservoir physical property goodness and difference of the horizontal well transformation section and the corresponding vertical well transformation layer section in the main stress direction of the block are judged, and the specific transformation type of each well group is determined; determining a well group transformation mode according to different transformation types of the well group; and according to the well group transformation mode, the specific seam distribution design of the well group is determined. According to the optimization design method for the straight-horizontal combined fracturing of the low-permeability and tight reservoir, an optimization design scheme is provided by analyzing and judging data of each straight well and each horizontal well in an existing well area, so that the straight wells and the horizontal wells can be reasonably transformed, the production degree and the fracture control volume of the reservoir are effectively improved, the development degree of the reservoir in the well area is improved, and the development period of the reservoir in the well area is shortened. Reserve loss is reduced, and production benefits are improved.

Description

Technical Field

[0001] The invention relates to the field of petroleum technology and oil production engineering, and in particular to a method for optimizing the design of straight-horizontal combined fracturing for low-permeability and dense reservoirs. Background Art

[0002] Low-permeability and tight reservoir blocks are mostly developed by single vertical well or single horizontal well. Single well type development has the problems of low reservoir utilization and large reserve loss, which affects the efficient development of the block. In the existing technology, for the development of ultra-low permeability and tight reservoirs, the vertical well spacing is generally more than 150 meters. Although the single vertical well type can ensure the development of the designed seams of each layer encountered by drilling, the remaining oil in the main layer between the well rows is difficult to be used; the single horizontal well type can effectively develop the main layer of the block, but the remaining layers cannot be developed. There is a lack of practical improvement plans and methods for the low-permeability and tight reservoir blocks that have been developed and drilled, and the potential of the reservoir cannot be fully utilized. Therefore, in view of the above shortcomings, a method for optimizing the design of vertical and horizontal combined fracturing for low-permeability and tight reservoirs is proposed. Summary of the invention

[0003] 1. Technical issues to be resolved In view of the shortcomings of the prior art, the present invention provides a method for optimizing the design of straight-horizontal combined fracturing in low-permeability and tight reservoirs, and provides a design scheme for optimizing and transforming developed low-permeability and tight reservoir blocks, thereby solving the problem that low-permeability and tight reservoir blocks are mostly developed by single vertical well or single horizontal well, and the single well type development has the problems of low reservoir utilization and large reserve loss, which affects the efficient development of the block.

[0004] (II) Technical solution In order to solve the above problems, the present invention provides a method for optimizing the design of straight-horizontal combined fracturing in low-permeability and dense reservoirs, comprising: Step 1: Determine the block transformation mode based on the characteristics of the block; Step 2: Determine the spacing between the surrounding vertical wells and horizontal wells; Step 3: Determine the difference in reservoir properties between the horizontal well reconstruction section and the corresponding vertical well reconstruction section in the direction of the principal stress of the block, and determine the specific reconstruction type of each well group; Step 4: Determine the transformation method of the well group according to the different transformation types of the well group; Step 5: Determine the specific seam layout design of the well group according to the well group transformation method; Step 6. To sum up, determine the optimization plan.

[0005] Furthermore, in step 1, when multiple layers are developed vertically, all horizontal wells are reconstructed, and the corresponding vertical well layers are not reconstructed. When the main layer developed vertically is prominent and the target layer of the horizontal well is also the main oil layer of the vertical well, the vertical-horizontal combined fracturing design is mainly used.

[0006] Furthermore, the spacing between the vertical well and the horizontal well is the distance between the vertical well and the horizontal well in the direction of maximum horizontal principal stress.

[0007] Furthermore, the physical properties include effective porosity, air permeability (mD), oil saturation, density logging (g / cm 3 ), acoustic time difference logging (μs / ft), deep resistivity logging (Ω·m) and effective thickness of single layer in vertical wells.

[0008] Furthermore, the transformation types are divided into level-excellent and direct-excellent transformation, level-differential and direct-excellent transformation, and level-excellent and direct-excellent transformation according to the physical properties.

[0009] Furthermore, in step 4, in the flat-excellent and straight-difference type reconstruction method, the horizontal wells are fractured, and the corresponding vertical well layers are not fractured; in the flat-difference and straight-excellent type reconstruction method, the horizontal wells are not fractured, and the corresponding vertical well layers are fractured; in the flat-excellent and straight-excellent type reconstruction method, the corresponding layers of both the horizontal wells and the vertical wells are fractured.

[0010] Furthermore, when determining the specific seam layout design in step five, in the flat superior straight difference type of transformation mode, the half-seam length is designed according to the distance between the surrounding vertical wells and horizontal wells in the principal stress direction minus 10 meters; in the flat difference straight superior type of transformation mode, the main seam projection of the horizontal section vertical well is not transformed within a certain distance, and normal fracturing transformation is performed outside the range, and the half-seam length is designed according to the distance between the surrounding vertical wells and horizontal wells in the principal stress direction minus 10 meters; in the flat superior straight superior type of transformation mode, the main seam projection of the horizontal section vertical well is not transformed within a certain distance, and the designed half-seam length is gradually increased to the distance between the target vertical well and the horizontal well in the principal stress direction minus 10 meters, and the horizontal well of the vertical well is transformed for the purpose of fracturing control scale, and the designed half-seam length is minus 20-30 meters between the target vertical well and the horizontal well in the principal stress direction.

[0011] (III) Beneficial effects The method for optimizing the design of vertical and horizontal combined fracturing for low-permeability and tight reservoirs provided by the present invention analyzes and judges the data of each vertical well and horizontal well in the existing well area, determines the transformation type and transformation method for each well independently, and then designs the seam layout for each well group, so as to reasonably transform the vertical wells and horizontal wells, effectively improve the reservoir utilization degree and seam control volume, improve the development degree of the reservoir in the well area, reduce reserve losses, and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a flow chart of the optimization design method of the straight-horizontal combined fracturing for low-permeability and tight reservoirs of the present invention; Figure 2 The well location map of the wells in block A in the embodiment of the straight-horizontal combined fracturing optimization design method for low-permeability and tight reservoirs of the present invention; Figure 3It is a schematic diagram of the optimization of fracturing of horizontal wells and corresponding vertical wells in block A in the embodiment of the method for optimizing the design of vertical and horizontal combined fracturing of low permeability and tight reservoirs of the present invention; Figure 4 It is a schematic diagram of the "flat superior straight difference type" fracturing optimization of Block A in the embodiment of the straight-flat combined fracturing optimization design method for low-permeability and tight reservoirs of the present invention; Figure 5 It is a schematic diagram of the "adjustment straight optimization type" fracturing optimization of Block A in the embodiment of the straight-flat combined fracturing optimization design method for low-permeability and tight reservoirs of the present invention; Figure 6 This is a schematic diagram of the "flat and straight" fracturing optimization of Block A in the embodiment of the straight and flat combined fracturing optimization design method for low-permeability and tight reservoirs of the present invention. Implementation

[0013] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0014] In the description of the present invention, it is necessary to understand that the orientations or positional relationships indicated by “upper”, “lower”, “inside”, “outside”, “top”, “bottom”, etc. are all based on the orientations or positional relationships shown in the accompanying drawings. The purpose is only to facilitate the description of the present invention and simplify the description. It does not indicate or imply that the referred parts must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0015] like Figure 1 As shown, the present invention provides a method for optimizing the design of straight-horizontal combined fracturing for low-permeability and dense reservoirs, which specifically includes: Step 1: Determine the block transformation mode based on the characteristics of the block; Among them, when multiple layers are developed vertically, fracturing follows the principle of maximizing the reserves of a single horizontal well, that is, all horizontal wells are remodeled, and the corresponding vertical well layers are not remodeled. When the main layer developed vertically is prominent and the target layer of the horizontal well is also the main oil layer of the vertical well, if the vertical well is not remodeled, the reserve loss will be large. At this time, the vertical-horizontal combined fracturing design is mainly used.

[0016] Step 2: Determine the spacing between the surrounding vertical wells and horizontal wells; Among them, the distance between the diameter and the horizontal well is determined according to the direction of the maximum horizontal principal stress of the block, and the distance between each vertical well and the horizontal well around the horizontal well is used as the basis for the design of the subsequent half-fracture length.

[0017] Step 3: Determine the difference in reservoir properties between the horizontal well reconstruction section and the corresponding vertical well reconstruction section in the direction of the principal stress of the block, and determine the specific reconstruction type of each well group; The physical properties include effective porosity, air permeability (mD), oil saturation, density logging (g / cm 3 ), acoustic time difference logging (μs / ft), deep resistance logging (Ω·m) and effective thickness of single layer of vertical well. In the process of evaluation, when the oil content is oil immersion, oil spot, sedimentary microfacies is main river channel, effective porosity ≥13%, air permeability ≥3.0mD, oil saturation ≥55%, density logging (g / cm3) ≤2.40, acoustic time difference logging (μs / ft) ≥80, deep resistance logging (Ω·m) ≥20, the horizontal section in the direction of principal stress of diameter is Class I (good); when the oil content is oil spot, sedimentary microfacies is non-main river channel, effective porosity is 12-13%, air permeability is 1.0-3.0mD, oil saturation is 50-55%, density logging (g / cm3) ≤2.40, When the acoustic time difference logging (μs / ft) is ≥80 and the deep resistivity logging (Ω·m) is 15-20, the horizontal section in the direction of the principal stress of the diameter is Class I (medium); when the oil content is oil trace, the sedimentary microfacies is non-main channel and inter-river, the effective porosity is 10-12%, the air permeability is 0.4-1.0mD, the oil saturation is 45-50%, the density logging (g / cm3) value is 2.40-2.45 (g / cm3), the acoustic time difference logging (μs / ft) value is 75-80, and the deep resistivity logging (Ω·m) is 10-15, the horizontal section in the direction of the principal stress of the diameter is Class II (medium).

[0018] Furthermore, the transformation types of the vertical wells are divided into flat-excellent straight-difference type, flat-excellent straight-excellent type and flat-excellent straight-excellent type. If the horizontal section of the principal stress direction of the vertical well is a Class I (good) or Class I (medium) reservoir, and the corresponding single-layer effective thickness of the vertical well is less than 2.5m, accounting for less than 30% of the effective thickness of the whole well, it is judged as "flat-excellent straight-difference type"; if the horizontal section of the principal stress direction of the vertical well is a Class I (medium) or Class II reservoir, and the single-layer effective thickness of the vertical well is greater than or equal to 2.5m, it is judged as "flat-excellent straight-excellent type"; if the horizontal section of the principal stress direction of the vertical well is a Class I (good) or Class I (medium) reservoir, and the single-layer effective thickness of the horizontal well target layer of the vertical well is greater than 2.5m, it is judged as "flat-excellent straight-excellent type".

[0019] Step 4: Determine the transformation method of the well group according to the different transformation types of the well group; Among them, when the transformation type of the well group is "flat, excellent, vertical and poor", in order to improve work efficiency while ensuring safety and normal production, the well group transformation method of horizontal well fracturing and non-fracturing of corresponding vertical well layers is adopted; when the transformation type of the well group is "flat, excellent, vertical and poor", the transformation method of non-fracturing of horizontal wells and fracturing of corresponding vertical well layers is used to concentrate the load in the transformation process on vertical wells with better strength, thereby improving work efficiency while ensuring safety and normal production; when the transformation type of the well group is "flat, excellent, vertical and poor", the physical properties of the vertical wells and horizontal wells of the well group are very good. At this time, the well group adopts a transformation method of fracturing the corresponding layers of both horizontal wells and vertical wells.

[0020] Step 5: Determine the specific seam layout design of the well group according to the well group transformation method; Among them, when determining the specific fracture layout design of the well group, if the horizontal well is fractured and the corresponding vertical well layer is not fractured, that is, the "flat superior and vertical inferior" transformation mode is used, the half fracture length is designed according to the distance between the surrounding vertical wells and the horizontal wells in the principal stress direction minus 10 meters, and the target layer of the horizontal well of the vertical well is not fractured; If the horizontal wells in the well group are not fractured, and the corresponding vertical wells are fractured, that is, the "adjustment straight optimization" transformation method, in order to ensure the integrity and normal operation of the horizontal wells after the transformation, the main fracture projection of the horizontal section of the vertical wells will not be transformed within a certain distance. In addition, the normal fracturing transformation is carried out, and the horizontal well target layer of the vertical well is fully fractured and transformed. The half-fracture length is designed according to the distance between the surrounding vertical wells and the horizontal wells in the main stress direction minus 10 meters; If the corresponding layers of the horizontal wells and vertical wells in the well group's transformation method are both fractured, that is, the "flat and vertical" transformation method is used, the main fracture of the horizontal vertical well will not be transformed within a certain distance of the projection, and the scale will gradually increase outward. The designed half-fracture length will gradually increase to the distance between the target vertical well and the horizontal well in the direction of the principal stress minus 10 meters. The horizontal well of the vertical well is transformed to a controlled scale of fracturing, and the designed half-fracture length will reduce the distance between the target vertical well and the horizontal well in the direction of the principal stress by 20-30 meters.

[0021] Among them, the non-reconstruction range within a certain distance of the main fracture projection of the horizontal vertical well needs to be designed according to the fracture wave width of the block. Generally, the ratio of the diameter of the non-reconstruction range and the distance between the target vertical well and the horizontal well is 1:3. If there is microseismic monitoring data in the target block that can observe the fracture detection wave width, the non-reconstruction area range is the fracture detection wave width.

[0022] Step 6. To sum up, determine the optimization plan.

[0023] After steps one to five, the obtained transformation patterns, vertical and horizontal well spacings, transformation types, transformation methods and seam layout designs are sorted and summarized to form the Zhiping combined fracturing optimization plan for the target low-permeability and tight reservoirs. Example

[0024] like Figure 2-6 As shown, taking Block A as an example, the operation process of the straight-horizontal combined fracturing optimization design method for low-permeability and tight reservoirs is demonstrated.

[0025] like Figure 2 As shown in the figure, Block A is a low-permeability block outside Daqing Oilfield. Due to ineffective water injection, insufficient formation energy, and rapid production decline, large-scale fracturing transformation is required. In order to increase the overall utilization of reserves, 4 additional horizontal wells were drilled.

[0026] Step 1: The target layer of the horizontal well in Block A is also the main oil layer of the vertical well, so it is judged that Block A needs to carry out vertical and horizontal combined fracturing optimization design.

[0027] Step 2: Figure 3 As shown, the direction of the maximum horizontal principal stress in Block A is nearly east-west, the development well pattern is 300m*150m, and the distance between each vertical well and the horizontal well around the horizontal well is 150m.

[0028] Step 3: After measuring the physical property data of each well in Block A, make a judgment and determine the transformation type of each well group in Block A. The result is that Block A contains all three types: "flat and direct difference type", "flat and direct difference type", and "flat and direct difference type". Among them, A-4 and A-6 wells belong to the "flat and direct difference type"; A-1, A-5, and A-11 wells belong to the "flat and direct difference type"; A-2, A-3, A-7, A-8, A-9, and A-10 wells belong to the "flat and direct difference type".

[0029] Step 4: Determine the transformation method for different transformation types based on the judgment results in step 3, where A-4 and A-6 wells are not fractured, and the corresponding horizontal well sections are fractured; A-1, A-5, and A-11 wells are fractured, and the corresponding sections of the horizontal wells are not fractured; A-2, A-3, A-7, A-8, A-9, and A-10 wells and the corresponding horizontal wells are fractured, and fractures are reasonably avoided.

[0030] Step 5. Determine the specific seam design based on the modification method.

[0031] like Figure 4 As shown, the FI5 layer of Wells A-4 and A-6 is not fractured, and the corresponding horizontal well layer section is fractured. The reasonable half-fracture length of the horizontal section is designed to be 140 meters (the distance between the surrounding vertical wells and the horizontal wells minus 10 meters, that is, 150 meters minus 10 meters); like Figure 5 As shown, for the FI5 layer fracturing in Wells A-1, A-5, and A-11, the reasonable half-fracture length of the vertical well reconstruction is designed to be 140 meters (the distance between the surrounding vertical wells and the horizontal wells minus 10 meters, that is, 150 meters minus 10 meters). According to the fracture monitoring sweep width of 30 meters, the main fracture of the horizontal section vertical well will not be reconstructed within 30 meters of the projection; like Figure 6As shown, the FI5 layer of wells A-2, A-3, A-7, A-8, A-9, and A-10 and the horizontal sections of the corresponding horizontal wells were all fractured, and fractures were avoided reasonably. The main fractures of the vertical wells in the horizontal sections were not reformed within 30 meters of the projection, and the scale was gradually increased outward. According to calculations, the designed half-fracture length was gradually increased to 140 meters (the distance between the surrounding vertical wells and horizontal wells was reduced by 10 meters, that is, 150 meters minus 10 meters). The horizontal wells of the vertical wells were reformed for the purpose of fracturing control scale, and the designed half-fracture length was 120 meters (the distance between the surrounding vertical wells and horizontal wells was reduced by 20-30 meters, that is, 150 meters minus 30 meters).

[0032] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for optimizing the design of straight-horizontal combined fracturing in low-permeability and dense reservoirs, characterized in that: include: Step 1: Determine the block transformation mode based on the characteristics of the block; Step 2: Determine the spacing between the surrounding vertical wells and horizontal wells; Step 3: Determine the difference in reservoir properties between the horizontal well reconstruction section and the corresponding vertical well reconstruction section in the direction of the principal stress of the block, and determine the specific reconstruction type of each well group; Step 4: Determine the transformation method of the well group according to the different transformation types of the well group; Step 5: Determine the specific seam layout design of the well group according to the well group transformation method; Step 6. To sum up, determine the optimization plan.

2. The method for optimizing the design of straight-horizontal combined fracturing for low-permeability and dense reservoirs according to claim 1, characterized in that: In the step 1, when multiple layers are developed vertically, all horizontal wells are reconstructed, and the corresponding vertical well layers are not reconstructed. When the main layer developed vertically is prominent and the target layer of the horizontal well is also the main oil layer of the vertical well, the vertical-horizontal combined fracturing design is mainly used.

3. The method for optimizing the design of straight-horizontal combined fracturing for low-permeability and dense reservoirs according to claim 1, characterized in that: The spacing between the vertical well and the horizontal well is the distance between the vertical well and the horizontal well in the direction of maximum horizontal principal stress.

4. The method for optimizing the design of straight-horizontal combined fracturing for low-permeability and dense reservoirs according to claim 1, characterized in that: The physical properties include effective porosity, air permeability (mD), oil saturation, density logging (g / cm 3 ), acoustic time difference logging (μs / ft), deep resistivity logging (Ω·m) and the corresponding single layer effective thickness.

5. The method for optimizing the design of straight-horizontal combined fracturing for low-permeability and dense reservoirs according to claim 4, characterized in that: According to the physical properties, the transformation types are divided into level-excellence and direct-excellence type transformation, level-differential and direct-excellence type transformation and level-excellence and direct-excellence type transformation.

6. The method for optimizing the design of straight-horizontal combined fracturing in low-permeability and dense reservoirs according to claim 5, characterized in that: In step 4, in the flat-excellent and straight-difference type of reconstruction, the horizontal wells are fractured, and the corresponding vertical well layers are not fractured; in the flat-difference and straight-excellent type of reconstruction, the horizontal wells are not fractured, and the corresponding vertical well layers are fractured; in the flat-excellent and straight-excellent type of reconstruction, the corresponding layers of both the horizontal wells and the vertical wells are fractured.

7. The method for optimizing the design of straight-horizontal combined fracturing in low-permeability and dense reservoirs according to claim 6, characterized in that: When determining the specific seam layout design in step five, in the flat superior straight difference type of reconstruction, the half-seam length is designed according to the distance between the surrounding vertical wells and horizontal wells in the direction of the principal stress minus 10 meters; in the flat difference straight superior type of reconstruction, the main seam projection of the horizontal section vertical well is not reconstructed within a certain distance, and normal fracturing reconstruction is carried out outside the range, and the half-seam length is designed according to the distance between the surrounding vertical wells and horizontal wells in the direction of the principal stress minus 10 meters; in the flat superior straight superior type of reconstruction, the main seam projection of the horizontal section vertical well is not reconstructed within a certain distance, and the designed half-seam length is gradually increased to the distance between the target vertical well and the horizontal well in the direction of the principal stress minus 10 meters, and the horizontal well of the vertical well is reconstructed for the purpose of fracturing control scale, and the designed half-seam length is 20-30 meters less than the distance between the target vertical well and the horizontal well in the direction of the principal stress.

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