Shale gas horizontal well segmentation and clustering fracturing parameter optimization method

Abstract

The invention discloses a segmented clustering fracturing parameter optimization method for a shale gas horizontal well, and belongs to the field of shale oil and gas development engineering.According to the method, on the basis of multi-stage fracture and fine depiction of different tectonic zones, three-dimensional geological modeling and hydraulic fracturing simulation are combined, and under the background of different tectonic positions and different fracture and crack combination modes, the fractures of different fractures and fractures are optimized; the invention relates to a fracturing parameter optimization technical method for variable section distance and variable cluster distance of a shale reservoir, which solves the problem of transverse heterogeneity of reservoir transformation in a segmented multi-cluster transformation process of a shale reservoir horizontal well, and has remarkable guiding significance for fracturing transformation of the shale reservoir and improvement of shale recovery efficiency.

Description

Technical Field

[0001] This application belongs to the field of shale oil and gas development engineering, and in particular relates to a method for optimizing the parameters of segmented and clustered fracturing of horizontal wells in shale gas in complex fractured areas. Background Technology

[0002] Volumetric fracturing technology for shale gas horizontal wells is of great significance for shale reservoir stimulation and has become a key technology for increasing the production and efficiency of low-permeability oil and gas. This technology has developed to the stage of multi-stage cluster fracturing construction. Practice has shown that this technology can significantly increase the oil drainage area of ​​the reservoir and maximize the recovery rate. In recent years, researchers have conducted relatively systematic research on multi-stage cluster fracturing technology for deep shale gas horizontal wells in the Sichuan Basin. Among them, Liu Yaowen, based on the characteristics of the shale reservoir in some blocks of Jiaoshiba, Fuling, such as large burial depth, high triaxial stress, and strong tectonic deformation, proposed the design concept of "small segment and dense cluster + large-diameter perforation" through gas reservoir numerical simulation and fracturing design simulation. Practice has proved that this fracturing design can effectively increase the fracture area, and the average fracture width and fracture network complexity after fracturing are significantly increased.

[0003] Meanwhile, during the implementation of fracturing, it was recognized that the size of the cluster spacing during horizontal well segmented fracturing has a significant impact on the fracturing effect of shale gas reservoirs (Gao Dongwei, 2019). Too small a cluster spacing design will lead to overlap of the fracturing zones between the main fractures of the clusters, reducing the fracturing efficiency; while too large a cluster spacing design will create unfracturing zones between the main fractures, affecting the reservoir's utilization.

[0004] Ren Lan, Lin Ran, Zhao Jinzhou, Wu Leize, and others pointed out that current cluster spacing optimization designs are mainly based on static models and target potential reservoir stimulation zones, without developing cluster spacing design methods that are consistent with actual fracturing processes and target dynamic reservoir stimulation volume (SRV). To address this, considering the coupled effects of fracture propagation, fracturing fluid loss, and stress interference, a dynamic SRV calculation model under cluster fracture propagation was established. The optimal SRV was used as the target for volumetric fracturing design to optimize the cluster spacing.

[0005] In recent years, segmented multi-cluster fracturing technology has been continuously deepened and developed in the volumetric fracturing of shale gas horizontal wells, achieving remarkable results and demonstrating good development prospects. It has become a key core technology for volumetric fracturing of horizontal wells. However, this method is mainly based on the theory of horizontal layered homogeneous shale reservoirs and does not take into account the influence of fractures and structures on fracturing construction technology. Therefore, at present, the construction method of uniform segmentation and close cutting and clustering is generally adopted when fracturing horizontal wells. There has been no relevant attempt or research on the segmentation and clustering construction technology for shale reservoirs with complex structures. This leads to the blind design of segmentation and cluster spacing parameters, resulting in large differences in fracturing effect and production capacity of each segment when fracturing shale horizontal wells, which to a certain extent restricts the effective implementation of volumetric fracturing technology for shale reservoirs. Summary of the Invention

[0006] The purpose of this application is to address the issue that shale reservoirs in complex structural zones are affected by fractures and tectonic deformation, resulting in strong lateral heterogeneity and significant differences in reservoir stimulation effects when fracturing in segments and clusters. This application discloses a method for optimizing segmented and clustered fracturing parameters in horizontal shale gas wells. By integrating geophysical exploration, geological analysis, geostress modeling, and hydraulic fracturing simulation calculations, this application proposes a variable cluster spacing fracturing construction technique with varying parameters such as segment length, cluster spacing, and fracturing intensity, tailored to different geological backgrounds with varying structural locations and natural fracture combinations. This approach has achieved good results.

[0007] The objective of this application is achieved through the following technical solution:

[0008] A method for optimizing fracturing parameters in a shale gas horizontal well using segmented and clustered fracturing techniques, comprising:

[0009] S1: Conduct earthquake fault prediction and evaluation at all levels, use the fault points encountered during drilling in the drilled wells to mark the earthquake attributes, and conduct earthquake prediction and characterization of faults at all levels.

[0010] S2: The original seismic tectonic stratigraphic densification interpretation is performed, and the stratigraphic densification is interpreted as 1*1 density. The trend surface method is used to carry out microstructural characterization and description, and to describe the lateral structural micro-undulations of the shale reservoir.

[0011] S3: Single-well geostress calculation and 3D modeling, improve the structural, property and natural fracture models within the platform area, carry out one-dimensional rock mechanics parameter calculation, and establish a three-dimensional integrated rock mechanics model of shale gas reservoir;

[0012] S4: Based on the three-dimensional integrated rock mechanics model of shale gas reservoirs, conduct hydraulic fracturing simulation and numerical simulation;

[0013] S5: By combining different construction parameters, calculate different structural locations, and optimize construction parameters such as horizontal well segment length, cluster spacing, and fluid intensity.

[0014] According to a preferred embodiment, step S1 includes:

[0015] Based on actual drilled fault points, we carried out noise reduction, directional filtering and fault imaging enhancement processing of post-stack seismic data to characterize multi-scale faults.

[0016] Various methods are used to optimize the seismic properties of faults at different scales, and different methods are used to characterize faults at different scales.

[0017] The reliability of fault prediction was verified using actual well drilling.

[0018] According to a preferred embodiment, in the process of verifying the reliability of fault prediction by actual drilling, faults at all levels are evaluated in stages and segments, and the faults are divided according to their nature and the size of the fault displacement.

[0019] According to a preferred embodiment, step S2 includes:

[0020] Based on the fracture characterization results and matching the microstructural deformation, the tectonic zone is divided into the main fracture surface, the strong tectonic deformation zone, the tectonic wing, and the tectonic gentle zone.

[0021] Based on the development of cracks, they are divided into strip-shaped unidirectional crack development zones, network-shaped crack development zones, and crack-undeveloped zones.

[0022] According to a preferred embodiment, step S3 includes:

[0023] Three-dimensional structural modeling: By integrating single-well, test and seismic data, a geometric model of shale gas structure is established through layer comparison and seismic interpretation, which is divided into layer model and fault model;

[0024] Shale reservoir modeling: Establish shale reservoir models including matrix porosity, permeability, TOC properties, adsorbed gas and free gas saturation properties, water saturation properties, and rock density properties.

[0025] DFN stochastic crack modeling: Establish a crack model with a series of attributes such as the location, orientation, shape, thickness, curvature, and matrix block attached to the multi-level crack sheet;

[0026] Three-dimensional integrated rock mechanics modeling of shale gas reservoirs: Based on the one-dimensional geomechanical modeling, a three-dimensional finite element geomechanical mesh is established according to the three-dimensional geological model. The three-dimensional geomechanical parameters are determined by using seismic inversion results and one-dimensional rock mechanics parameter calculation results, including Young's modulus, Poisson's ratio, uniaxial compressive strength, tensile strength, and friction angle parameters.

[0027] According to a preferred embodiment, step S4 includes: based on the three-dimensional integrated rock mechanics model of the shale gas reservoir, conducting hydraulic fracturing simulation and numerical simulation, improving the dynamic and static models through dynamic history fitting, and based on the improved model, optimizing the reasonable fracturing section length and cluster spacing of the horizontal well by comprehensively considering economic benefits and actual engineering conditions.

[0028] According to a preferred embodiment, the parameters optimized in step S5 include: pre-drilling, pre-pressing, and production parameters.

[0029] The aforementioned main solution and its various further alternative solutions can be freely combined to form multiple solutions, all of which are solutions that can be adopted and are claimed in this application. Those skilled in the art, after understanding the solution of this application, will realize that there are many combinations based on the prior art and common general knowledge, all of which are technical solutions to be protected in this application, and will not be exhaustively listed here.

[0030] The beneficial effects of this application are:

[0031] The method described in this application utilizes the fault points encountered during drilling in the well to calibrate seismic attributes, carry out multi-level fault earthquake prediction and characterization, and simultaneously conduct micro-amplitude structural characterization and description, finely characterizing and evaluating different structural morphologies, thereby significantly improving the prediction accuracy and precision of multi-level faults.

[0032] This application method references the interpretation results of multi-level fractures and micro-structures, and adopts an integrated geological-engineering approach to optimize fracturing parameters for different risk sections in horizontal wells. This effectively guides the design of differentiated fracturing parameters for shale gas horizontal wells, significantly reduces the cross-flow rate and casing deformation rate, and significantly increases gas production. Attached Figure Description

[0033] Figure 1 This is a comparison chart of fracturing parameters before and after optimization in shale reservoirs with complex geological structures. Detailed Implementation

[0034] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, unless otherwise specified, the following embodiments and features in the embodiments can be combined with each other.

[0035] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, this application should indicate that unless otherwise specified, the structures, connections, positions, power sources, etc., involved in this application are all things that a person skilled in the art could discover without inventive effort based on existing technology.

[0036] This application discloses a method for optimizing the parameters of segmented and clustered fracturing in shale gas horizontal wells. The method includes the following steps.

[0037] Step S1: Conduct earthquake fault prediction and evaluation at all levels. Use the faults encountered during drilling in the existing wells to identify earthquake attributes and conduct earthquake prediction and characterization of faults at all levels.

[0038] Specifically, based on the fault enhancement processing of seismic data, we carried out multi-method and multi-attribute optimization, multi-method series prediction and characterization of multi-level faults and fractures, accurately calibrated the fault breakpoint locations using drilled wells, evaluated the fault level, and carried out fault classification and segmentation evaluation.

[0039] Preferably, step S1 includes: based on actual drilled fault points, performing denoising, steering filtering, and fault imaging enhancement processing on post-stack seismic data, thereby making small-scale fault points more concise and characterizing multi-scale faults, significantly improving fault prediction accuracy. Various methods are selected to reflect the seismic attributes of faults at different scales, and faults at each scale are characterized for different methods; and actual drilling is used to verify the reliability of fault point prediction.

[0040] Furthermore, during the process of verifying the reliability of fault prediction through actual drilling, faults at all levels were evaluated in stages and segments, and the faults were classified according to their nature and displacement. Specifically, faults with a displacement greater than 8m were classified as large-scale faults, and those with a displacement less than 8m were classified as medium- and small-scale faults.

[0041] Step S2: Refine the original seismic tectonic horizons and interpret them as 1*1 density. Use the trend surface method to characterize and describe the microstructures and the lateral structural undulations of the shale reservoir.

[0042] Preferably, step S2 includes:

[0043] A detailed stratigraphic interpretation of the strong reflection interface at the bottom boundary of the Wufeng Formation should be carried out, with an interpretation accuracy of 1*1 density.

[0044] Calculations of tectonic trend surfaces were performed to highlight microstructural deformation zones.

[0045] Based on the fracture characterization results and matching the microstructural deformation, the tectonic zone is divided into the main fracture surface, the strong tectonic deformation zone, the tectonic wing, and the tectonic gentle zone.

[0046] Based on the development of cracks, they are divided into strip-shaped unidirectional crack development zones, network-shaped crack development zones, and crack-undeveloped zones.

[0047] Step S3: Calculate the geostress of a single well and perform 3D modeling. Improve the model of structure, properties and natural fractures within the platform area, perform 1D rock mechanics parameter calculations, and establish a 3D integrated rock mechanics model of the shale gas reservoir.

[0048] Preferably, step S3 includes:

[0049] Three-dimensional structural modeling: By integrating single-well, test and seismic data, a geometric model of shale gas structure is established through layer comparison and seismic interpretation, which is divided into layer model and fault model;

[0050] Shale reservoir modeling: Establish shale reservoir models including matrix porosity, permeability, TOC properties, adsorbed gas and free gas saturation properties, water saturation properties, and rock density properties.

[0051] DFN stochastic crack modeling: Establish a crack model with a series of attributes such as the location, orientation, shape, thickness, curvature, and matrix block attached to the multi-level crack sheet;

[0052] Three-dimensional integrated rock mechanics modeling of shale gas reservoirs: Based on the one-dimensional geomechanical modeling, a three-dimensional finite element geomechanical mesh is established according to the three-dimensional geological model. The three-dimensional geomechanical parameters are determined by using seismic inversion results and one-dimensional rock mechanics parameter calculation results, including Young's modulus, Poisson's ratio, uniaxial compressive strength, tensile strength, and friction angle parameters.

[0053] Step S4: Based on the three-dimensional integrated rock mechanics model of shale gas reservoirs, conduct hydraulic fracturing simulation and numerical simulation.

[0054] Preferably, step S4 includes: based on the three-dimensional integrated rock mechanics model of the shale gas reservoir, conducting hydraulic fracturing simulation and numerical simulation, improving the dynamic and static models through dynamic history fitting, and based on the improved model, optimizing the reasonable fracturing section length and cluster spacing of the horizontal well by comprehensively considering economic benefits and actual engineering conditions.

[0055] Step S5: By combining different construction parameters, calculate different structural locations, and optimize construction parameters such as horizontal well segment length, cluster spacing, and fluid intensity.

[0056] Preferably, the optimized parameters in step S5 include: pre-drilling, pre-fracturing, and production parameters. The parameter design is based on the fracture and micro-structural zoning characteristics of complex structural zones. Following the construction concept of "segmentation by structure, subdivision and cutting of each segment, control of fluid volume, and high-intensity sand addition," reasonable values ​​are selected based on the optimal combination of different fracturing construction parameters. For fracture surfaces, micro-structural axes, micro-structural flanks, gently sloping areas, areas with developed strip fractures, and areas with developed network fractures, construction scale parameters such as flow rate, fluid intensity, and sand addition intensity are combined respectively to achieve the optimal fracturing stimulation effect on shale. (Reference) Figure 1 As shown, Figure 1 This is a comparison chart of fracturing parameters before and after optimization in shale reservoirs with complex geological structures. The left side of the chart is a schematic diagram before optimization, and the right side is a schematic diagram after optimization.

[0057] Based on the detailed characterization of multi-level fractures and different structural zones, this application method combines three-dimensional geological modeling and hydraulic fracturing simulation to develop a fracturing parameter optimization technique for shale reservoirs with varying segment spacing and cluster spacing under different structural locations and fracture and fracture combinations. This method solves the problem of lateral heterogeneity in reservoir stimulation during segmented multi-cluster stimulation of shale reservoirs and has significant guiding significance for fracturing stimulation of shale reservoirs and improving shale recovery.

[0058] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for optimizing fracturing parameters in segmented and clustered shale gas horizontal wells, characterized in that, The method for optimizing the staged and clustered fracturing parameters of shale gas horizontal wells includes: S1: Conduct earthquake fault prediction and evaluation at all levels, use the fault points encountered during drilling in the drilled wells to mark the earthquake attributes, and conduct earthquake prediction and characterization of faults at all levels. S2: The original seismic tectonic stratigraphic densification interpretation is performed, and the stratigraphic densification is interpreted as 1*1 density. The trend surface method is used to carry out microstructural characterization and description, and to describe the lateral structural micro-undulations of the shale reservoir. S3: Single-well geostress calculation and 3D modeling, improve the structural, property and natural fracture models within the platform area, carry out one-dimensional rock mechanics parameter calculation, and establish a three-dimensional integrated rock mechanics model of shale gas reservoir; S4: Based on the three-dimensional integrated rock mechanics model of shale gas reservoirs, conduct hydraulic fracturing simulation and numerical simulation; S5: By combining different construction parameters, calculate different structural locations, and optimize the construction parameters of horizontal well segment length, cluster spacing, and fluid intensity.

2. The method for optimizing fracturing parameters in shale gas horizontal wells by segmentation and clustering as described in claim 1, characterized in that, Step S1 includes: Based on actual drilled fault points, we carried out noise reduction, directional filtering and fault imaging enhancement processing of post-stack seismic data to characterize multi-scale faults. Various methods are employed to reflect the seismic properties of faults at different scales, and faults at different scales are characterized for each method. The reliability of fault prediction was verified using actual well drilling.

3. The method for optimizing fracturing parameters in shale gas horizontal wells by segmentation and clustering as described in claim 2, characterized in that, In the process of verifying the reliability of fault prediction through actual drilling, faults at all levels are evaluated in stages and segments, and the faults are classified according to their nature and fault displacement.

4. The method for optimizing fracturing parameters in segmented clusters of shale gas horizontal wells as described in claim 1, characterized in that, Step S2 includes: Based on the fracture characterization results and matching the microstructural deformation, the tectonic zone is divided into the main fracture surface, the strong tectonic deformation zone, the tectonic wing, and the tectonic gentle zone. Based on the development of cracks, they are divided into strip-shaped unidirectional crack development zones, network-shaped crack development zones, and crack-undeveloped zones.

5. The method for optimizing fracturing parameters in shale gas horizontal wells by segmentation and clustering as described in claim 1, characterized in that, Step S3 includes: Three-dimensional structural modeling: By integrating single-well, test and seismic data, a geometric model of shale gas structure is established through layer comparison and seismic interpretation, which is divided into layer model and fault model; Shale reservoir modeling: Establish shale reservoir models including matrix porosity, permeability, TOC properties, adsorbed gas and free gas saturation properties, water saturation properties, and rock density properties. DFN stochastic crack modeling: Establish a crack model that includes the location, orientation, shape, thickness, curvature, and a series of properties of the matrix block to which the multi-level crack sheet is attached; Three-dimensional integrated rock mechanics modeling of shale gas reservoirs: Based on the one-dimensional geomechanical modeling, a three-dimensional finite element geomechanical mesh is established according to the three-dimensional geological model. The three-dimensional geomechanical parameters are determined by using seismic inversion results and one-dimensional rock mechanics parameter calculation results, including Young's modulus, Poisson's ratio, uniaxial compressive strength, tensile strength, and friction angle parameters.

6. The method for optimizing fracturing parameters in shale gas horizontal wells by segmentation and clustering as described in claim 1, characterized in that, Step S4 includes: Based on the three-dimensional integrated rock mechanics model of shale gas reservoirs, hydraulic fracturing simulation and numerical simulation were carried out. The dynamic and static models were improved through dynamic history fitting. Based on the improved model, the reasonable fracturing section length and cluster spacing of horizontal wells were optimized by comprehensively considering economic benefits and actual engineering conditions.

7. The method for optimizing fracturing parameters in shale gas horizontal wells by segmentation and clustering as described in claim 1, characterized in that, The parameters optimized in step S5 include: pre-drilling, pre-pressing, and production parameters.

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