Coal bed gas reservoir self-adapting volume fracturing reconstruction and mining method

Abstract

The present application relates to coalbed methane development technical field, specifically disclose a kind of coalbed methane reservoir self-adapting volume fracturing reconstruction and mining method, collect the contour line of coal seam floor of target point, fracture and fissure distribution, natural fissure orientation and density and other microstructure data;Respectively carry out structure curvature inversion and ground stress orientation solution, obtain structure curvature disturbance value and stress anisotropy index;Two are matched with space vector cross, according to gradient same direction superposition area and different direction cancellation area is divided into fissure dominant reconstruction domain and stress dominant reconstruction domain;Volume fracturing is implemented to fissure dominant reconstruction domain, and directional adjustment of perforation phase is implemented to stress dominant reconstruction domain The fracturing of steering, and stop matching domain outer fracturing operation;Finally, drainage mining is mined;The present application solves the problem that existing fracturing reconstruction and microstructure do not match.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane development technology, specifically to a method for adaptive volumetric fracturing stimulation and extraction of coalbed methane reservoirs. Background Technology

[0002] In the field of deep coalbed methane development, the effectiveness of reservoir stimulation directly affects the production of single wells and development benefits. Currently, the development of vertical coalbed methane wells mainly relies on regional structural interpretation results and logging data for fracturing design. It usually focuses on matching well patterns and engineering parameters. After delineating favorable areas on larger structural units, a unified fracturing scale, displacement, and perforation scheme are directly adopted for construction.

[0003] In existing technologies, coalbed methane vertical well reservoir stimulation schemes are mainly formulated based on regional tectonic interpretation results, lacking refined evaluation methods for the spatial distribution characteristics of micro-structures within the target scale. This results in the inability to match corresponding stimulation methods according to the geomechanical response characteristics of different reservoir areas during fracturing operations, leading to ineffective injection of fracturing fluid and proppant in inefficient stimulation zones, and low targeting and effectiveness of stimulation measures. Summary of the Invention

[0004] The purpose of this invention is to provide an adaptive volumetric fracturing stimulation and exploitation method for coalbed methane reservoirs to solve the problems mentioned above.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] An adaptive volumetric fracturing stimulation and exploitation method for coalbed methane reservoirs includes the following steps:

[0007] S1, collect micro-structural data of the target reservoir, including coal seam floor contour lines, fault and fracture distribution, and the orientation and density of natural fractures;

[0008] S2, perform tectonic curvature inversion and geostress orientation calculation on the micro-tectonic data respectively, and obtain the tectonic curvature disturbance value and stress anisotropy index accordingly;

[0009] S3, the structural curvature perturbation value and the stress anisotropy index are cross-matched in space vectors. Based on the gradient homogeneous superposition zone and gradient anisotropic cancellation zone in the matching domain, the reservoir is divided into fracture-dominated modification domain and stress-dominated modification domain.

[0010] S4. Based on the planar distribution of the fracture-dominated modification domain and the stress-dominated modification domain, volumetric fracturing with the first displacement of liquid is carried out in the fracture-dominated modification domain, and directional fracturing with perforation phase orientation adjustment is carried out in the stress-dominated modification domain, and fracturing operation on the reservoir outside the matching domain is terminated.

[0011] S5 is used for drainage and extraction of the fracturing reservoir.

[0012] As a further aspect of the present invention: the process of obtaining the constructed curvature perturbation value is as follows:

[0013] Based on the contour lines of the coal seam floor, extract the extreme points of curvature of each contour line;

[0014] Using the curvature extremum points as seed points, we expand outward along the contour line normal direction, and trace the boundary where the curvature decays to zero layer by layer to define the disturbance influence radius corresponding to each curvature extremum point.

[0015] All curvature values ​​within the radius of influence of the disturbance are spatially superimposed with the curvature values ​​at each curvature extremum point, and the average value of the superimposed curvature field is used as the constructed curvature disturbance value of the corresponding target point.

[0016] As a further aspect of the present invention: the extraction of the curvature extrema points of each contour line specifically includes:

[0017] By sequentially tracing the tangent azimuth of each point along each contour line, the turning sequence of each contour line is obtained;

[0018] The local extreme points of the rate of change of the angle in the angle sequence are used as the initial curvature extreme points;

[0019] Using the initial curvature extremum point as a reference, and combining the normal direction offset of adjacent contour lines in the same area, the initial curvature extremum points with offset deviations exceeding the threshold are filtered out, and the final curvature extremum points are obtained.

[0020] As a further aspect of the present invention: the process for obtaining the stress anisotropy index is as follows:

[0021] Based on the orientation and density of natural fractures, the spatial orientation parameters of each fracture group were extracted;

[0022] Based on the spatial attitude parameters, the stress component difference of the geostress field in the normal and tangential directions of each fracture group is calculated, and the difference between the maximum and minimum values ​​of the stress component difference of each fracture group is taken as the anisotropic strength value of the fracture group.

[0023] The spatial weighted average of the anisotropic intensity values ​​of all crack groups is used as the stress anisotropy index of the target point.

[0024] As a further aspect of the present invention: the extraction process of the spatial attitude parameters is as follows:

[0025] Based on the orientation and density of natural fractures, spatial vector clustering is performed on each natural fracture to obtain multiple initial fracture groups and their corresponding principal values ​​of spatial orientation.

[0026] A topological search is performed on the adjacent tangent relationships of each natural fracture within each initial fracture group, and natural fractures with tangent relationships are merged into the same fracture system.

[0027] The combination of the principal azimuth value, mean density value, and mean dip angle value of all natural fractures within each fracture system is used as the spatial attitude parameter corresponding to each fracture group.

[0028] As a further aspect of the present invention: the process of performing spatial vector cross-matching is as follows:

[0029] Centered on the target point, the constructed curvature perturbation value is anisotropically decomposed along each radial direction to obtain the curvature perturbation vector components in each radial direction.

[0030] The stress anisotropy index is decomposed along the same radial direction to obtain the stress anisotropy vector components in each radial direction.

[0031] In the same radial direction, the curvature disturbance vector component and the stress anisotropy vector component are superimposed in each direction. The radial direction in which the vector superposition result is in the same direction is defined as the gradient in the same direction superposition region, and the radial direction in which the vector superposition result is in the opposite direction is defined as the gradient in opposite direction cancellation region.

[0032] Based on the vector superposition results in each radial direction, the spatial connectivity boundary of the same-direction superposition zone is traced around the target point and defined as the planar distribution range of the crack-dominated transformation domain. The spatial connectivity boundary of the opposite-direction offset zone is traced and defined as the planar distribution range of the stress-dominated transformation domain.

[0033] As a further aspect of the present invention: the process for obtaining the curvature perturbation vector components is as follows:

[0034] Centered on the target point, the contour lines of the coal seam floor are divided into radial sections at azimuth intervals. The curvature value and radial distance of all intersections between each radial section and the contour lines are then extracted.

[0035] Based on the curvature values ​​of all intersection points on each radial tangent, the rate of decay of the curvature values ​​with radial distance is taken as the radial rate of change of curvature of the radial tangent.

[0036] The radial sections with positive curvature radial change rates are retained, and the product of the curvature radial change rate of each retained radial section and the azimuth direction vector is used as the curvature perturbation vector component in the corresponding radial direction.

[0037] As a further aspect of the present invention: the volumetric fracturing of the fracture-dominant modification domain with a first displacement of fluid specifically includes:

[0038] Based on the spatial distribution of fracture groups within the fracture-dominant modification domain, the modification domain is divided into several sequentially initiating fracture segments along the fracture direction.

[0039] Fracturing is initiated sequentially from the wellbore towards the distal well, and fracturing fluid is injected in a stepped manner with increasing flow rate. Each flow rate is continuously used to fracture until the wellhead pressure response is stable, and then the flow rate is increased to the next level.

[0040] The final stage displacement is used as the first displacement, and the liquid volume under the first displacement is used to complete the pumping of the entire modified area.

[0041] As a further aspect of the present invention: the directional fracturing that adjusts the perforation phase orientation in the stress-dominant modification domain specifically includes:

[0042] Based on the anisotropic vector components of stress in each radial direction within the stress-dominant modification domain, the location of the minimum value of the vector component is used as the reference for perforation phase adjustment.

[0043] After the perforation holes are laid out at a predetermined angle away from the reference orientation, cracks are induced to propagate along the second smallest value of the stress anisotropic vector component.

[0044] During the steering and expansion process, the pumping volume and flow rate are maintained after the perforation phase adjustment to complete the injection.

[0045] As a further aspect of the present invention: the drainage and extraction of the fracturing reservoir specifically includes:

[0046] In the initial stage of drainage, the pump hanger is lowered at the first liquid reduction rate to establish the first pressure reduction funnel in the fracture-dominated modification zone.

[0047] When the first pressure-reducing funnel expands to the boundary of the stress-dominant modification domain, the liquid drop rate is switched to the second liquid drop rate, which is lower than the first liquid drop rate.

[0048] Continue drainage at the second liquid rate, and establish a second depressurization funnel in the stress-dominant transformation zone, so that the first depressurization funnel and the second depressurization funnel are connected at the boundary.

[0049] During the connection maintenance period, the gas production is controlled by a constant casing pressure to complete the extraction.

[0050] The beneficial effects of this invention are:

[0051] (1) This invention collects multi-source micro-tectonic data, including coal seam floor contour lines, fault and fracture distribution, and the orientation and density of natural fractures, and performs tectonic curvature inversion and geostress orientation calculation to obtain tectonic curvature disturbance values ​​and stress anisotropy indices. This provides refined geological input for subsequent fracturing stimulation based on the local tectonic features of the target point. Compared with methods that directly rely on regional tectonic background or single seismic interpretation results for fracturing design, this invention can more accurately characterize the curvature field changes and geostress anisotropy response caused by micro-tectonic features at the target point, which is beneficial to improving the matching degree between subsequent fracturing stimulation measures and reservoir geological conditions.

[0052] (2) Based on the spatial vector cross-matching results of structural curvature disturbance values ​​and stress anisotropy indices, this invention divides the reservoir into fracture-dominated and stress-dominated fracturing domains. For each domain, stepped-volume fracturing with increased displacement and perforation phase-oriented fracturing are employed, while fracturing operations on reservoirs outside the matched domains are terminated. This differentiated fracturing strategy matches the corresponding fracturing method according to the geomechanical response characteristics of different reservoir regions, avoiding ineffective fracturing operations in non-fracturing domains, thereby reducing the blindness and operating costs of fracturing operations. Attached Figure Description

[0053] The invention will now be further described with reference to the accompanying drawings.

[0054] Figure 1 This is a flowchart of the method of the present invention;

[0055] Figure 2 This is a flowchart of the process for obtaining the curvature perturbation value in this invention;

[0056] Figure 3 This is a flowchart illustrating the process of obtaining the stress anisotropy index in this invention. Detailed Implementation

[0057] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] Please see Figure 1 As shown, this invention is a method for adaptive volumetric fracturing stimulation and exploitation of coalbed methane reservoirs, comprising the following steps:

[0059] S1, collect micro-structural data of the target reservoir, including coal seam floor contour lines, fault and fracture distribution, and the orientation and density of natural fractures;

[0060] S2, perform tectonic curvature inversion and geostress orientation calculation on the micro-tectonic data respectively, and obtain the tectonic curvature disturbance value and stress anisotropy index accordingly;

[0061] S3, the structural curvature perturbation value and the stress anisotropy index are cross-matched in space vectors. Based on the gradient homogeneous superposition zone and gradient anisotropic cancellation zone in the matching domain, the reservoir is divided into fracture-dominated modification domain and stress-dominated modification domain.

[0062] S4. Based on the planar distribution of the fracture-dominated modification domain and the stress-dominated modification domain, volumetric fracturing with the first displacement of liquid is carried out in the fracture-dominated modification domain, and directional fracturing with perforation phase orientation adjustment is carried out in the stress-dominated modification domain, and fracturing operation on the reservoir outside the matching domain is terminated.

[0063] S5 is used for drainage and extraction of the fracturing reservoir.

[0064] In S1, micro-structural data of the target reservoir are collected, including coal seam floor contour lines, fault and fracture distribution, and the orientation and density of natural fractures, specifically including:

[0065] The contour data of the coal seam floor are extracted based on the 3D seismic exploration results of the block where the target reservoir is located.

[0066] A three-dimensional seismic network is deployed within the block. After collecting seismic data, it is processed through static correction, amplitude compensation, deconvolution, migration stacking, etc., to obtain a three-dimensional seismic data volume.

[0067] Based on this data, the reflection layers of the coal seam floor are interpreted by in-phase axis tracking to obtain the reflection time layers of the coal seam floor. Time-depth conversion is performed by combining the sonic logging velocity data, and elevation correction is performed based on the wellhead core elevation to generate a contour map of the coal seam floor with elevation and depth as the vertical axis.

[0068] The fracture and fissure distribution data were obtained by jointly interpreting the variance and coherence properties of the 3D seismic data volume.

[0069] Variance and coherence slices are extracted along the reflective strata of the coal seam floor. The spatial overlap of high anomaly bands on the variance volume and low coherence bands on the coherence volume is used as the development location of fractures or fissures. The orientation of each overlapped band is traced and combined in planar view to obtain the distribution trajectory of each fracture and fissure on the coal seam floor.

[0070] The location and density data of natural fractures are obtained based on imaging logging data of the target reservoir. After drilling and completion at the target point, an imaging logging instrument is run down to acquire microresistivity scanning images of the entire wellbore. From the images, the occurrence of natural fractures on the wellbore is identified and extracted, including the fracture strike azimuth, dip angle, and aperture.

[0071] The cumulative number of fractures in each azimuth interval of the entire well section is counted, and the ratio of the cumulative number of fractures in each azimuth interval to the width of the statistical azimuth interval is used as the fracture density.

[0072] After the above-mentioned micro-tectonic data were collected, the contour lines of the coal seam floor, the distribution trajectory of faults and fissures, and the orientation and density data of natural fissures were uniformly incorporated into the spatial database of the target points. Spatial registration was performed using the same geodetic coordinate reference and depth reference to form a target point micro-tectonic dataset for subsequent analysis.

[0073] Please see Figure 2 or Figure 3 As shown in Figure S2, tectonic curvature inversion and stress azimuth calculation are performed on the micro-tectonic data to obtain the tectonic curvature perturbation value and stress anisotropy index, specifically including:

[0074] Based on the contour lines of the coal seam floor, extract the curvature extreme points of each contour line, and sequentially trace the tangent azimuth of each point along each contour line to obtain the turning sequence of each contour line;

[0075] The local extreme points of the rate of change of the angle in the angle sequence are used as the initial curvature extreme points;

[0076] Using the initial curvature extremum point as a reference, and combining the normal direction offset of adjacent contour lines in the same area, the initial curvature extremum points with offset deviations exceeding the threshold are filtered out, and the final curvature extremum points are obtained.

[0077] The offset deviation is defined as the ratio of the offset of the normal direction of adjacent contour lines at the same location to the straight-line distance between the two points. The threshold value is set to be no more than 0.15 for this ratio. This value is obtained by statistically analyzing the average deviation between the measured formation dip angle data of drilled wells in this block and the normal direction of the contour lines. Specifically, the angle between the measured formation dip angle direction of each drilled well in this block and the normal direction of the corresponding contour line is calculated, and the average value of the tangent of this angle is multiplied by 0.6 as the threshold value.

[0078] Using the curvature extremum points as seed points, the curves are expanded outward along the contour normal direction, and the boundary where the curvature decays to zero is traced layer by layer to define the disturbance influence radius corresponding to each curvature extremum point.

[0079] Specifically, starting from the location of the seed point, the system gradually advances outward in steps of 1 meter along the contour line normal. At each step, the curvature value at the current advancing position is extracted and compared with the curvature value of the seed point. When the curvature value at the current advancing position decays to less than 5% of the curvature value of the seed point, the straight-line distance between the advancing position and the seed point is marked as the decay boundary distance of the seed point in the normal direction.

[0080] After obtaining all attenuation boundary distances in all normal directions around the seed point, the average value of the attenuation boundary distances in each direction is taken as the disturbance influence radius corresponding to the seed point.

[0081] All curvature values ​​within the radius of influence of the disturbance are spatially superimposed with the curvature values ​​at each curvature extremum point, and the average value of the superimposed curvature field is used as the constructed curvature disturbance value of the target point.

[0082] Specifically, after determining the spatial coordinates of the target point, the target point is used as the center, and the weighted average of the perturbation influence radii of each curvature extremum point is used as the search radius. Within this search radius, the curvature values ​​of all grid nodes and the curvature values ​​at each curvature extremum point are extracted. The arithmetic mean of all extracted curvature values ​​is taken, and this arithmetic mean is the construction curvature perturbation value of the target point.

[0083] In the weighted average, the weight of each disturbance radius is determined based on the ratio of the absolute value of the curvature at that curvature extremum point to the sum of the absolute values ​​of the curvature at all curvature extremum points.

[0084] The calculation process for the above curvature field mean is determined by the following mathematical expression:

[0085] Assume that there are multiple targets within the target search radius. The curvature value sampling points, of which the first The curvature value of each sampling point is denoted as Then the construction curvature perturbation value of the target point Calculated using the following formula:

[0086] ;

[0087] in, For the search radius, For the first The radial distance from each sampling point to the target point This represents the total number of curvature value sampling points within the search radius. For the first The curvature value at each sampling point To construct the curvature perturbation value, this The value is used to characterize the intensity of the combined curvature field disturbance caused by the influence of local micro-structures on the target point.

[0088] The process of obtaining the stress anisotropy index is as follows:

[0089] Spatial orientation parameters of each fracture group were extracted based on the orientation and density of natural fractures.

[0090] Spatial vector clustering was performed on each natural fracture, and natural fractures with an azimuth difference of less than 15 degrees and a dip difference of less than 10 degrees were grouped into the same initial fracture group, thus obtaining multiple initial fracture groups and their corresponding spatial azimuth principal values.

[0091] A topological search is performed on the adjacent tangent relationships of each natural fracture within each initial fracture group, and natural fractures with tangent relationships are merged into the same fracture system.

[0092] The combination of the principal azimuth value, mean density value, and mean dip angle value of all natural fractures within each fracture system is used as the spatial attitude parameter corresponding to each fracture group.

[0093] Among them, the principal azimuth value is the circular average of the azimuth angles of all natural fractures in the initial fracture group, the average density value is the ratio of the number of natural fractures in the initial fracture group to the spatial distribution area of ​​the group, and the average dip angle is the arithmetic mean of the dip angles of all natural fractures in the initial fracture group.

[0094] Based on the spatial attitude parameters, the stress component differences of the geostress field in the normal and tangential directions of each fracture group are calculated.

[0095] Specifically, the triaxial principal stress values ​​at the target point are obtained, and these triaxial principal stress values ​​are projected onto the normal and tangential directions of each fracture group to obtain the normal effective stress and tangential effective stress. The difference between the normal effective stress and the tangential effective stress is calculated as the stress component difference of the fracture group.

[0096] The difference between the maximum and minimum values ​​of the stress components of each fracture group is taken as the anisotropic strength value of that fracture group.

[0097] The spatial weighted average of the anisotropic intensity values ​​of all crack groups is used as the stress anisotropy index of the target point.

[0098] Specifically, the product of the cumulative number of natural fractures in each fracture group and the spatial distribution area of ​​the fracture group is used as the spatial weight of the fracture group. The anisotropic intensity values ​​of all fracture groups are weighted and summed according to the spatial weight, and then divided by the sum of the spatial weights of all fracture groups. The resulting quotient is the stress anisotropy index.

[0099] The calculation process of the above spatially weighted mean is determined by the following mathematical expression:

[0100] Assume that there are common features around the target point. The first fracture group, of which the second... The anisotropic strength values ​​of each fracture group are denoted as follows: The spatial weight of this fracture group is denoted as Then the stress anisotropy index of the target point Calculated using the following formula:

[0101] ;

[0102] in, For the first Spatial weights of each fracture group For the first Anisotropic strength values ​​of each fracture group The total number of fracture groups around the target point. The stress anisotropy index is... The value is used to characterize the combined anisotropic intensity of geostress under the influence of multiple sets of fractures at the target point.

[0103] In S3, the structural curvature perturbation value and the stress anisotropy index are cross-matched using spatial vectors. Based on the gradient homogeneous superposition region and gradient anisotropic cancellation region within the matching domain, the reservoir is divided into fracture-dominated and stress-dominated modification domains, specifically including:

[0104] The process of obtaining the curvature disturbance vector components is as follows: with the target point as the center, the contour lines of the coal seam floor are divided into 24 radial sections at 15-degree azimuth intervals. Each radial section is a vertical section extending outward from the target point along a certain azimuth angle. This section intersects the contour lines at multiple intersection points.

[0105] The curvature value and radial distance of all intersection points of each radial section with the contour line are extracted. The radial distance is the horizontal projection distance from the intersection point to the target point.

[0106] Based on the curvature values ​​of all intersection points on each radial section, the rate of decay of the curvature values ​​with radial distance is taken as the radial rate of change of curvature of the radial section. The decay rate is calculated as follows: take the sequence of curvature values ​​and radial distances of all intersection points on the radial section, calculate the ratio of the difference in curvature values ​​between adjacent intersection points to the difference in radial distances from the near target point to the far target point, and take the arithmetic mean of all adjacent ratios as the radial rate of change of curvature of the radial section.

[0107] Radial sections with positive radial curvature change rates are retained, while those with zero or negative radial curvature change rates are discarded. The product of the radial curvature change rate of each retained radial section and the azimuth direction vector is used as the curvature disturbance vector component in the corresponding radial direction, where the azimuth direction vector is a unit vector and its direction is consistent with the azimuth of the radial section.

[0108] The process of obtaining the stress anisotropy vector components is as follows: the stress anisotropy index is decomposed along the same 24 radial directions.

[0109] Specifically, for each radial direction, the projection coefficients of the normal directions of all crack groups in that radial direction are obtained, and the arithmetic mean of each projection coefficient is used as the stress distribution coefficient in that radial direction.

[0110] The stress anisotropy vector component in the radial direction is obtained by multiplying the stress anisotropy index of the target point by the stress distribution coefficient in the radial direction.

[0111] The stress distribution coefficient ranges from 0 to 1, and the sum of the stress distribution coefficients in all 24 radial directions equals 1.

[0112] The process of directional vector superposition and gradient region definition is as follows: In the same radial direction, the curvature disturbance vector component and the stress anisotropy vector component are superimposed directionally.

[0113] The operation of vector superposition is as follows: in the same radial direction, the magnitude of the curvature disturbance vector component is added to the magnitude of the stress anisotropy vector component, and the orientation of the superposition result is consistent with the radial direction.

[0114] If the curvature perturbation vector component and the stress anisotropy vector component point in the same direction in the radial direction, the superposition result will be in the same direction.

[0115] If the directions are opposite, the superposition result will be in the opposite direction. The radial direction in which the superposition result is in the same direction is defined as the gradient superposition region, and the radial direction in which the superposition result is in the opposite direction is defined as the gradient cancellation region.

[0116] The process of defining the planar distribution range of the modification domain is as follows: based on the vector superposition results in all 24 radial directions, the spatial connectivity boundary of the same-direction superposition area is traced around the target point and defined as the planar distribution range of the crack-dominated modification domain, and the spatial connectivity boundary of the opposite-direction offset area is traced and defined as the planar distribution range of the stress-dominated modification domain.

[0117] The method for tracking the spatial connectivity boundary is as follows: with the target point as the center, all 24 radial directions are traversed in order of increasing azimuth angle. Continuous radial directions that are determined to be in the same direction superposition area are assigned to the same same direction continuous segment, and continuous radial directions that are determined to be in the opposite direction cancellation area are assigned to the same opposite direction continuous segment.

[0118] The arithmetic mean of the radial distances in all radial directions within a continuous segment in the same direction is taken as the boundary radius of the segment. The fan-shaped area enclosed by this boundary radius and the starting and ending azimuth angles is taken as the planar distribution range of the dominant fissure modification domain.

[0119] The arithmetic mean of the radial distances in all radial directions within the non-directional continuous segment is taken as the boundary radius of the segment. The fan-shaped area enclosed by this boundary radius and the starting and ending azimuth angles is taken as the planar distribution range of the stress-dominant modification domain.

[0120] If the magnitude of the vector superposition result in a certain radial direction is 0, then that radial direction is not included in any continuous segment.

[0121] In S4, based on the planar distribution of the fracture-dominated and stress-dominated fracturing domains, volumetric fracturing with the first displacement of fluid is performed on the fracture-dominated domain, and directional fracturing with perforation phase adjustment is performed on the stress-dominated domain. Fracturing operations on reservoirs outside the matching domain are then terminated. Specifically, this includes:

[0122] The volumetric fracturing process of the fracture-dominant modification domain is as follows: based on the spatial distribution of fracture groups within the fracture-dominant modification domain, the fracture-dominant modification domain is divided into several sequentially initiating fracture segments along the fracture direction.

[0123] Centered on the target wellbore, the modified area is divided into the first fracture initiation segment, the second fracture initiation segment, and so on up to the Nth fracture initiation segment along the fracture direction with a segment length of 30 meters from the wellbore to the far well. The width of each fracture initiation segment on the plane is the normal span of the fracture group distribution trajectory within that segment.

[0124] Fracturing is initiated sequentially from the wellbore towards the distal well, with fracturing fluid injected in a stepped manner. Each level of fracturing continues until the wellhead pressure response stabilizes before the next level of fracturing is increased.

[0125] The first fracturing section was injected with fracturing fluid at a rate of 6 cubic meters per minute. During the injection process, the wellhead pressure was continuously monitored. When the fluctuation of the wellhead pressure within 5 consecutive minutes did not exceed 0.5 MPa, it was determined that the wellhead pressure response at this rate had stabilized, and the rate was increased to 8 cubic meters per minute.

[0126] The second fracture section was injected at a rate of 8 cubic meters per minute, and the rate was increased to 10 cubic meters per minute after the wellhead pressure response stabilized.

[0127] The displacement is increased step by step according to this pattern, with each level increasing by 2 cubic meters per minute. The amount of fluid injected at each level is the product of the spatial distribution area of ​​the fracture group in the fracture initiation section and the standard value of the amount of fluid to be injected per square meter. The standard value of the amount of fluid to be injected per square meter is set at 0.8 cubic meters based on the statistical results of previous fracturing operations in this block.

[0128] Once the displacement reaches 16 cubic meters per minute and the wellhead pressure response at that displacement level stabilizes, 16 cubic meters per minute will be used as the final displacement level, and no further increases will be made.

[0129] The final stage displacement is used as the first displacement, and the liquid volume under the first displacement is used to complete the pumping of the entire modified area.

[0130] The liquid volume corresponding to the final stage displacement is the product of the total area of ​​the fracture-dominant modification domain and the standard value of the liquid volume required per square meter, minus the sum of the liquid volumes already injected in each fracture initiation segment. The difference is the liquid volume required to be injected under the final stage displacement.

[0131] The liquid is continuously injected at a rate of 16 cubic meters per minute until the entire area of ​​the fracture-dominant modification zone is pumped.

[0132] The directional fracturing process in the stress-dominated modification domain is as follows: based on the anisotropic stress vector components in each radial direction within the stress-dominated modification domain, the orientation of the minimum value of the vector component is used as the reference for perforation phase adjustment.

[0133] Within the planar distribution range of the stress-dominated modification domain, the amplitudes of all 24 radial stress anisotropic vector components are extracted, and the amplitudes are arranged in ascending order. The radial direction with the smallest amplitude is taken as the reference orientation for perforation phase adjustment.

[0134] If there are multiple radial directions with equal amplitude and all at the minimum value, the direction with the middle azimuth angle is taken as the reference azimuth.

[0135] After the perforation holes are arranged at a predetermined angle away from the reference orientation, cracks are induced to propagate along the second smallest value of the stress anisotropic vector component.

[0136] The predetermined angle is determined based on the angle between the reference azimuth and the second smallest value azimuth of the stress anisotropic vector component. In the ascending order of the amplitudes of the stress anisotropic vector components in all radial directions, the radial direction corresponding to the second smallest amplitude is selected, and the angle between the reference azimuth and the second smallest value azimuth is calculated. This angle is used as the predetermined angle by which the perforation hole deviates from the reference azimuth.

[0137] During perforation operations, a cable is used to transport the perforating gun. After positioning the perforating gun in the target layer, the phase angle of the perforating gun is set according to the perforation phase adjustment benchmark and the predetermined angle, so that the perforation holes are arranged on the well wall in a direction that deviates from the benchmark orientation by a predetermined angle.

[0138] When fracturing occurs, fracturing fluid is ejected from the orifice. After the orifice is set off from the reference orientation, the direction of fracturing initiation is pulled by the orifice direction, deviating from the original principal stress direction, and extending along the second smallest value of the stress anisotropic vector component.

[0139] During the diversion and expansion process, the pumping rate and fluid volume are maintained after the perforation phase adjustment. After the perforation phase adjustment, a constant pumping rate of 12 cubic meters per minute is used as the constant pumping rate for diversion fracturing. The total pumping volume is the product of the total area of ​​the stress-dominant modified domain and the standard value of the required injection volume per square meter. The constant pumping rate is maintained until the total pumping volume is fully injected.

[0140] Fracturing operations terminated for reservoirs outside the matching domain: Fracturing operations are terminated for reservoirs outside the matching domain in S3 that are not classified into the fracture-dominated or stress-dominated modification domains.

[0141] Before fracturing operations, based on the two types of modified domain planar distribution ranges defined in S3, identify the azimuth and radial distance ranges of the modified domains around the target point that are not covered. Within this range, no perforation operations, no fracturing fluid injection, and no fracturing operations are performed.

[0142] In S5, the fracturing reservoir is drained and exploited, specifically including:

[0143] In the initial stage of drainage, the pump hanger is lowered at the first liquid reduction rate to establish the first pressure reduction funnel in the fracture-dominated transformation zone.

[0144] The first fluid reduction rate is set based on the development density of natural fractures in the fracture-dominated modification zone. Specifically, the cumulative number of natural fractures per meter of well section in the fracture-dominated modification zone is counted, and the integer value is obtained by dividing the cumulative number by 10. The product of this integer value and 5 meters per day is used as the first fluid reduction rate.

[0145] During the pump lowering process, the expansion status of the pressure reduction funnel is tracked by monitoring the bottom hole pressure daily. When the bottom hole pressure drops to 1.2 times the coal seam desorption pressure, it is determined that the first pressure reduction funnel has been established in the fracture-dominated stimulation domain.

[0146] When the first pressure-reducing funnel expands to the boundary of the stress-dominant modification domain, the liquid drop rate is switched to a second liquid drop rate, which is lower than the first liquid drop rate.

[0147] Specifically, a pressure monitoring point is set at the boundary of the stress-dominant modification zone. This monitoring point is a downhole pressure gauge placed at the boundary to collect the fluid pressure value at that location in real time.

[0148] When the fluid pressure measured at the monitoring point drops to 85% of the initial pressure, it is determined that the first pressure-reducing funnel has expanded to the boundary of the stress-dominant modification domain. At this point, the liquid reduction rate is switched to the second liquid reduction rate. The value of the second liquid reduction rate is 60% of the first liquid reduction rate, rounded down to the nearest integer.

[0149] Continue drainage at the second liquid rate, and establish a second pressure-reducing funnel within the stress-dominant transformation domain, so that the first pressure-reducing funnel and the second pressure-reducing funnel are connected at the boundary.

[0150] The pump hanger continues to be lowered at the second liquid reduction rate, and the range of the second pressure reduction funnel is gradually expanded within the stress-dominated modification zone. The pressure monitoring point at the boundary of the stress-dominated modification zone is continuously monitored. When the difference between the fluid pressure measured at the monitoring point and the bottom hole flowing pressure is less than 0.1 MPa, it is determined that the first pressure reduction funnel and the second pressure reduction funnel have been connected at the boundary.

[0151] During the connection maintenance period, the gas production is controlled by a constant casing pressure to complete the extraction.

[0152] During the connection maintenance period, the constant casing pressure value is determined based on the difference between the coal seam desorption pressure and the bottom hole flowing pressure. Specifically, on the first day of connection maintenance, the difference between the current coal seam desorption pressure and the bottom hole flowing pressure is obtained, and 85% of this difference is used as the constant casing pressure value.

[0153] The casing pressure is kept constant by adjusting the opening of the wellhead throttle valve. The gas production is monitored daily. When the gas production decreases by more than 5% for three consecutive days, the constant casing pressure is lowered by 0.1 MPa and then kept constant again until production is completed.

[0154] The working principle of this invention is as follows: Micro-structural data of the target reservoir is collected, including coal seam floor contour lines, fracture and fissure distribution, and the orientation and density of natural fractures. Based on the micro-structural data, structural curvature inversion and geostress orientation calculation are performed to obtain structural curvature perturbation values ​​and stress anisotropy indices. The structural curvature perturbation values ​​and stress anisotropy indices are then spatially vector cross-matched. Based on the gradient superposition zone and gradient anisotropy cancellation zone within the matching domain, the reservoir is divided into fracture-dominated and stress-dominated fracturing domains. Based on the planar distribution of the fracture-dominated and stress-dominated fracturing domains, volumetric fracturing with a first-volume flow rate is performed on the fracture-dominated fracturing domain, and directional fracturing with perforation phase orientation adjustment is performed on the stress-dominated fracturing domain. Fracturing operations on reservoirs outside the matching domain are terminated. The fractured reservoir is then drained and exploited.

[0155] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for adaptive volumetric fracturing stimulation and exploitation of coalbed methane reservoirs, characterized in that, Includes the following steps: S1, collect micro-structural data of the target reservoir, including coal seam floor contour lines, fault and fracture distribution, and the orientation and density of natural fractures; S2, perform tectonic curvature inversion and geostress orientation calculation on the micro-tectonic data respectively, and obtain the tectonic curvature disturbance value and stress anisotropy index accordingly; S3, the structural curvature perturbation value and the stress anisotropy index are cross-matched in space vectors. Based on the gradient homogeneous superposition zone and gradient anisotropic cancellation zone in the matching domain, the reservoir is divided into fracture-dominated modification domain and stress-dominated modification domain. S4. Based on the planar distribution of the fracture-dominated modification domain and the stress-dominated modification domain, volumetric fracturing with the first displacement of liquid is carried out in the fracture-dominated modification domain, and directional fracturing with perforation phase orientation adjustment is carried out in the stress-dominated modification domain, and fracturing operation on the reservoir outside the matching domain is terminated. S5 is used for drainage and extraction of the fracturing reservoir.

2. The adaptive volumetric fracturing stimulation and exploitation method for coalbed methane reservoirs according to claim 1, characterized in that, The process for obtaining the constructed curvature perturbation value is as follows: Based on the contour lines of the coal seam floor, extract the extreme points of curvature of each contour line; Using the curvature extremum points as seed points, we expand outward along the contour line normal direction, and trace the boundary where the curvature decays to zero layer by layer to define the disturbance influence radius corresponding to each curvature extremum point. All curvature values ​​within the radius of influence of the disturbance are spatially superimposed with the curvature values ​​at each curvature extremum point, and the average value of the superimposed curvature field is used as the constructed curvature disturbance value of the corresponding target point.

3. The adaptive volumetric fracturing stimulation and exploitation method for coalbed methane reservoirs according to claim 2, characterized in that, The extraction of the curvature extrema points of each contour line specifically includes: By sequentially tracing the tangent azimuth of each point along each contour line, the turning sequence of each contour line is obtained; The local extreme points of the rate of change of the angle in the angle sequence are used as the initial curvature extreme points; Using the initial curvature extremum point as a reference, and combining the normal direction offset of adjacent contour lines in the same area, the initial curvature extremum points with offset deviations exceeding the threshold are filtered out, and the final curvature extremum points are obtained.

4. The adaptive volumetric fracturing stimulation and exploitation method for coalbed methane reservoirs according to claim 1, characterized in that, The process for obtaining the stress anisotropy index is as follows: Based on the orientation and density of natural fractures, the spatial orientation parameters of each fracture group were extracted; Based on the spatial attitude parameters, the stress component difference of the geostress field in the normal and tangential directions of each fracture group is calculated, and the difference between the maximum and minimum values ​​of the stress component difference of each fracture group is taken as the anisotropic strength value of the fracture group. The spatial weighted average of the anisotropic intensity values ​​of all crack groups is used as the stress anisotropy index of the target point.

5. The adaptive volumetric fracturing stimulation and exploitation method for coalbed methane reservoirs according to claim 4, characterized in that, The extraction process of the spatial attitude parameters is as follows: Based on the orientation and density of natural fractures, spatial vector clustering is performed on each natural fracture to obtain multiple initial fracture groups and their corresponding principal values ​​of spatial orientation. A topological search is performed on the adjacent tangent relationships of each natural fracture within each initial fracture group, and natural fractures with tangent relationships are merged into the same fracture system. The combination of the principal azimuth value, mean density value, and mean dip angle value of all natural fractures within each fracture system is used as the spatial attitude parameter corresponding to each fracture group.

6. The adaptive volumetric fracturing stimulation and exploitation method for coalbed methane reservoirs according to claim 1, characterized in that, The process of performing spatial vector cross-matching is as follows: Centered on the target point, the constructed curvature perturbation value is anisotropically decomposed along each radial direction to obtain the curvature perturbation vector components in each radial direction. The stress anisotropy index is decomposed along the same radial direction to obtain the stress anisotropy vector components in each radial direction. In the same radial direction, the curvature disturbance vector component and the stress anisotropy vector component are superimposed in each direction. The radial direction in which the vector superposition result is in the same direction is defined as the gradient in the same direction superposition region, and the radial direction in which the vector superposition result is in the opposite direction is defined as the gradient in opposite direction cancellation region. Based on the vector superposition results in each radial direction, the spatial connectivity boundary of the same-direction superposition zone is traced around the target point and defined as the planar distribution range of the crack-dominated transformation domain. The spatial connectivity boundary of the opposite-direction offset zone is traced and defined as the planar distribution range of the stress-dominated transformation domain.

7. The adaptive volumetric fracturing stimulation and exploitation method for coalbed methane reservoirs according to claim 6, characterized in that, The process of obtaining the curvature perturbation vector components is as follows: Centered on the target point, the contour lines of the coal seam floor are divided into radial sections at azimuth intervals. The curvature value and radial distance of all intersections between each radial section and the contour lines are then extracted. Based on the curvature values ​​of all intersection points on each radial tangent, the rate of decay of the curvature values ​​with radial distance is taken as the radial rate of change of curvature of the radial tangent. The radial sections with positive curvature radial change rates are retained, and the product of the curvature radial change rate of each retained radial section and the azimuth direction vector is used as the curvature perturbation vector component in the corresponding radial direction.

8. The adaptive volumetric fracturing stimulation and exploitation method for coalbed methane reservoirs according to claim 1, characterized in that, The volumetric fracturing of the fracture-dominant modification domain with a first-volume flow rate specifically includes: Based on the spatial distribution of fracture groups within the fracture-dominant modification domain, the modification domain is divided into several sequentially initiating fracture segments along the fracture direction. Fracturing is initiated sequentially from the wellbore towards the distal well, and fracturing fluid is injected in a stepped manner with increasing flow rate. Each flow rate is continuously used to fracture until the wellhead pressure response is stable, and then the flow rate is increased to the next level. The final stage displacement is used as the first displacement, and the liquid volume under the first displacement is used to complete the pumping of the entire modified area.

9. The adaptive volumetric fracturing stimulation and exploitation method for coalbed methane reservoirs according to claim 1, characterized in that, The aforementioned directional fracturing, which involves adjusting the perforation phase orientation in the stress-dominant modification domain, specifically includes: Based on the anisotropic vector components of stress in each radial direction within the stress-dominant modification domain, the location of the minimum value of the vector component is used as the reference for perforation phase adjustment. After the perforation holes are laid out at a predetermined angle away from the reference orientation, cracks are induced to propagate along the second smallest value of the stress anisotropic vector component. During the steering and expansion process, the pumping volume and flow rate are maintained after the perforation phase adjustment to complete the injection.

10. The adaptive volumetric fracturing stimulation and exploitation method for coalbed methane reservoirs according to claim 1, characterized in that, The aforementioned process of draining and exploiting the fracturing reservoir specifically includes: In the initial stage of drainage, the pump hanger is lowered at the first liquid reduction rate to establish the first pressure reduction funnel in the fracture-dominated modification zone. When the first pressure-reducing funnel expands to the boundary of the stress-dominant modification domain, the liquid drop rate is switched to the second liquid drop rate, which is lower than the first liquid drop rate. Continue drainage at the second liquid rate, and establish a second depressurization funnel in the stress-dominant transformation zone, so that the first depressurization funnel and the second depressurization funnel are connected at the boundary. During the connection maintenance period, the gas production is controlled by a constant casing pressure to complete the extraction.

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