CN113586019A - Fracturing optimization method and device for shale gas reservoir and computer storage medium - Google Patents
Fracturing optimization method and device for shale gas reservoir and computer storage medium Download PDFInfo
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- E21B43/25—Methods for stimulating production
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
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Abstract
The disclosure provides a fracturing optimization method and device for a shale gas reservoir and a computer storage medium, and belongs to the field of shale gas exploration and development. The fracturing optimization method comprises the following steps: determining the bedding development strength of a shale gas storage layer section to be evaluated, wherein the bedding development strength refers to the degree of formation, development and existence of a layered structure generated by the change of rocks along the vertical direction along with the change of time; determining the bedding joint development strength of the shale gas storage layer section to be evaluated, wherein the bedding joint development strength refers to the degree of formation, development and existence of various layer seams formed due to uneven rock structures along with time change; and optimizing the fracturing scheme of the shale gas storage interval to be evaluated based on the bedding development strength and the bedding seam development strength of the shale gas storage interval to be evaluated.
Description
Technical Field
The disclosure relates to the field of shale gas exploration and development, and in particular relates to a fracturing optimization method and device for a shale gas reservoir and a computer storage medium.
Background
In the field of petroleum, fracturing (also called hydraulic fracturing) refers to a method for forming cracks in oil and gas layers by utilizing the hydraulic action in the process of oil extraction or gas production. Fracturing is a stimulation and transformation means of shale gas reservoirs. In order to obtain good reservoir fracturing effect and avoid blind fracturing, the fracturing process parameters (including the amount of fracturing fluid and the number of perforation holes) of the shale gas reservoir must be explored first.
In the related art, the fracturing process parameters of shale gas reservoirs are mostly analyzed based on logging data (including rock tensile strength, pore pressure, horizontal minimum stress and the like).
With the strategic transition from shallow to deep of shale gas exploration and development, the shale gas hydraulic fracturing surface is faced with the difficult problems of complex geological conditions such as high stress, deep burial and the like, and the fracturing optimization method provided by the related technology has poor application effect under the complex geological conditions.
Disclosure of Invention
The embodiment of the disclosure provides a fracturing optimization method and device for a shale gas reservoir and a computer storage medium, which can adapt to the optimization of a fracturing scheme of the shale gas reservoir under complex geological conditions. The technical scheme is as follows:
in one aspect, a fracturing optimization method for a shale gas reservoir is provided, and the fracturing optimization method comprises the following steps:
determining the bedding development strength of a shale gas storage layer section to be evaluated, wherein the bedding development strength refers to the degree of formation, development and existence of a layered structure generated by the change of rocks along the vertical direction along with the change of time;
determining the bedding joint development strength of the shale gas storage layer section to be evaluated, wherein the bedding joint development strength refers to the degree of formation, development and existence of various layer seams formed due to uneven rock structures along with time change;
and optimizing the fracturing scheme of the shale gas storage interval to be evaluated based on the bedding development strength and the bedding seam development strength of the shale gas storage interval to be evaluated.
Optionally, the determining the bedding development strength of the shale gas reservoir section to be evaluated includes:
acquiring the weight of physical property data relative to the layering development strength, wherein the physical property data refers to data related to the appearance and the property of an object;
acquiring physical property data of the shale gas storage layer section to be evaluated;
and calculating the bedding development strength of the shale gas storage interval to be evaluated based on the weight of the physical data relative to the bedding development strength and the physical data of the shale gas storage interval to be evaluated.
Optionally, the obtaining of the weight of the physical property data relative to the intensity of the stratigraphic development comprises:
acquiring an image of a rock slice of each coring well sample, wherein the coring well sample is a rock sample in a coring well of a well zone where the shale gas reservoir section to be evaluated is located;
determining the bedding development strength of each core well sample based on the image of the rock slice of each core well sample;
obtaining physical property data of each core well sample;
determining a weight of the physical property data relative to the bedding development strength based on the bedding development strength of each cored well sample and the physical property data of each cored well sample.
Optionally, the determining the bedding development strength of each core well sample based on the image of the rock slice of each core well sample comprises:
determining the number of streaks of each of the core well samples based on the image of the rock slice of each of the core well samples;
determining the pixel mean value of the grayed images of the rock slices of the various core well samples based on the images of the rock slices of the various core well samples;
and calculating the bedding development strength of each core well sample based on the number of the striae of each core well sample and the pixel mean value of the grayed image of the rock slice of each core well sample.
Optionally, the determining the number of streaks for each of the core well samples based on the image of the rock slice for each of the core well samples comprises:
meshing the images of the rock slices of the core well samples according to the target mesh size;
graying the image of the rock slice of each core well sample;
counting the number of unit grids with pixel values larger than a target threshold value in each row of unit grids after graying, wherein the unit grids in the same row are parallel to the extending direction of a single rock stratum;
and when the number of the unit grids with the pixel values of two adjacent rows larger than the target threshold is respectively larger than and smaller than the target number, adding one to the number of the thread layers of the corresponding sample.
Optionally, the determining the bedding joint development strength of the shale gas storage interval to be evaluated includes:
acquiring the weight of the physical property data relative to the development strength of the bedding seams;
acquiring physical property data of the shale gas storage layer section to be evaluated;
and calculating the bedding seam development strength of the shale gas storage interval to be evaluated based on the bedding development strength of the shale gas storage interval to be evaluated, the weight of the physical property data relative to the bedding seam development strength and the physical property data of the shale gas storage interval to be evaluated.
Optionally, the obtaining of the weight of the physical property data relative to the development strength of the bedding joint comprises:
acquiring an image of a rock slice of each coring well sample, wherein the coring well sample is a rock sample in a coring well of a well zone where the shale gas reservoir section to be evaluated is located;
determining the bedding joint development strength of each core well sample based on the image of the rock slice of each core well sample;
obtaining physical property data of each core well sample;
and determining the weight of the physical property data relative to the bedding joint development strength based on the bedding development strength of the shale gas storage interval to be evaluated, the bedding joint development strength of each core well sample and the physical property data of each core well sample.
Optionally, the optimizing a fracturing scheme of the shale gas storage interval to be evaluated based on the bedding development strength and the bedding fracture development strength of the shale gas storage interval to be evaluated includes:
calculating a natural weak surface index of the shale gas storage layer section to be evaluated based on the bedding development intensity index and the bedding seam development intensity of the shale gas storage layer section to be evaluated;
when the natural weak surface index is lower than a first target value, enhancing the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated;
when the natural weak plane development strength is higher than the first target value and lower than a second target value, maintaining the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated, wherein the first target value is smaller than the second target value;
and when the development strength of the natural weak plane is higher than the second target value, weakening the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated.
In a second aspect, a fracture optimization device for a shale gas reservoir is provided, the fracture optimization device comprising:
the first determination module is used for determining the bedding development strength of the shale gas storage layer section to be evaluated, wherein the bedding development strength refers to the degree of the formation, development and existence of a layered structure generated by the change of rock along the vertical direction along with the change of time;
the second determination module is used for determining the bedding joint development strength of the shale gas storage layer section to be evaluated, wherein the bedding joint development strength refers to the degree of formation, development and existence of various layer internal joints formed due to uneven rock structure along with time change;
and the evaluation module is used for optimizing the fracturing scheme of the shale gas storage interval to be evaluated based on the bedding development strength and the bedding crack development strength of the shale gas storage interval to be evaluated.
In a third aspect, a fracturing optimization device for a shale gas reservoir is provided, the fracturing optimization device comprising: a memory, a processor and a computer program stored in the memory and executable on the processor, the processor being configured to implement the aforementioned method of fracture optimization of a shale gas reservoir when executing the computer program.
In a fourth aspect, a computer storage medium is provided, in which at least one instruction is stored, and the instruction is loaded and executed by a processor to implement the method for fracture optimization of a shale gas reservoir.
The technical scheme provided by the embodiment of the disclosure has the following beneficial effects:
the bedding development strength and the bedding joint development strength of the shale gas storage layer section to be evaluated are determined, the bedding development strength and the bedding joint development strength can represent the development strength of a natural weak surface, and the natural weak surface is an important characteristic of geology, so that the geological understanding of complex geological conditions (high stress, deep burying and the like) can be accurately realized; and optimizing the fracturing scheme of the shale gas reservoir section to be evaluated based on the bedding development strength and the bedding joint development strength of the shale gas reservoir section to be evaluated, so that the fracturing operation efficiency and the yield increasing effect are improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present disclosure, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
Fig. 1 is a flow chart of a method for fracture optimization of a shale gas reservoir provided by an embodiment of the present disclosure;
fig. 2 is a flow chart of a method for fracture optimization of a shale gas reservoir provided by an embodiment of the present disclosure;
FIG. 3 is a schematic diagram of an image processing flow provided by an embodiment of the present disclosure;
fig. 4 is a structural block diagram of a fracturing optimization device for a shale gas reservoir provided by an embodiment of the present disclosure;
fig. 5 is a structural block diagram of a fracturing optimization device for a shale gas reservoir provided by an embodiment of the present disclosure.
Detailed Description
To make the objects, technical solutions and advantages of the present disclosure more apparent, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.
First, explanations of terms related to the embodiments of the present invention will be described.
The weak surface, i.e., the stress-weakened surface, refers to a surface which is likely to be broken or slid when subjected to stress.
Bedding, refers to the layered structure resulting from the change of rock in the vertical direction.
The strength of the development of the laminae refers to the degree of formation, development and existence of the laminae over time.
Bedding joints, also known as interbedded joints, refer to various interbedded joints formed due to uneven rock structure.
The development strength of the bedding joint refers to the degree of formation, development and existence of the bedding joint along with the change of time.
Physical property data refers to data relating to the appearance and properties of a material, for example, physical property data of a shale gas reservoir interval includes siliceous mineral content, carbonate content, pyrite content, and Total Organic Carbon (TOC) content.
In order to meet shale gas reservoir evaluation under complex geological conditions (high stress, deep burying and the like), high-precision geological knowledge needs to be realized, wherein the geological knowledge comprises rules in various aspects such as determination of development characteristics (including development strength of a natural weak surface) of the natural weak surface, fracture mechanics of intersection of natural fractures and hydraulic fractures and the like. The developmental features of the natural facets have not been effectively predicted and identified. For example, the bedding is a natural weak surface, and there is no clear numerical calculation method to realize quantitative characterization, so that the analysis of the rule of the bedding (the form of the development strength of the bedding in the longitudinal direction) is lagged. Moreover, for natural fractures, the current geophysical measures can only predict natural fracture zones with the size of 20m or more, and natural fractures with the size of a meter or below which are actually intersected with hydraulic fractures can hardly be effectively predicted or characterized. Therefore, in the fracturing optimization method for the shale gas reservoir provided by the embodiment, the development strength (including the bedding development strength and the bedding fracture development strength) of the natural weak face in the shale gas reservoir can be effectively represented, and the method has great significance in the aspects of fracturing design optimization and the like.
Fig. 1 is a flowchart of a method for optimizing fracturing of a shale gas reservoir provided in an embodiment of the present disclosure. Referring to fig. 1, the fracture optimization method flow includes the following steps.
The shale gas reservoir section to be evaluated may be each shale gas reservoir section of a horizontal section in a shale gas horizontal well. The fracturing is one of well modification means of a horizontal section in a shale gas horizontal well.
And 102, determining the bedding seam development strength of the shale gas reservoir section to be evaluated.
And 103, optimizing a fracturing scheme for evaluating the shale gas storage interval to be evaluated based on the bedding development strength and the bedding crack development strength of the shale gas storage interval to be evaluated.
In the embodiment, the bedding development strength and the bedding joint development strength of the shale gas storage interval to be evaluated are determined, the bedding development strength and the bedding joint development strength can represent the development strength of a natural weak surface, and the natural weak surface is an important characteristic of geology, so that the geological understanding of complex geological conditions (high stress, deep burying and the like) can be accurately realized; and optimizing the fracturing scheme of the shale gas reservoir section to be evaluated based on the bedding development strength and the bedding joint development strength of the shale gas reservoir section to be evaluated, so that the fracturing operation efficiency and the yield increasing effect are improved.
Fig. 2 is a flowchart of a method for optimizing fracturing of a shale gas reservoir provided by an embodiment of the present disclosure. Referring to fig. 2, the flow of the fracture optimization method includes the following steps.
The physical property data of the shale gas reservoir section to be evaluated comprises the siliceous mineral content, the carbonate content, the pyrite content and the Total Organic Carbon (TOC) content of the shale gas reservoir section to be evaluated. The siliceous mineral content may be equal to the sum of the quartz content and the feldspar content, and the carbonate content may be equal to the sum of the calcite content and the dolomite content.
The physical property data of the shale gas storage interval to be evaluated can be obtained from the logging interpretation data of the shale gas storage interval to be evaluated.
In this example, the weight is the degree of importance of the physical property data with respect to the intensity of the lamellar development or the intensity of the lamellar gap development. Optionally, the determining manner of the weight is not limited in this embodiment, and the weight may be preset in the computer by an engineer according to experience, or may be calculated by the computer through data of a large number of samples.
The embodiment provides a mode of respectively calculating the weight of the physical property data relative to the bedding development strength and the weight of the physical property data relative to the bedding seam development strength through a large number of coring well samples, and the coring well samples can be rock samples in a coring well of a well zone where the shale gas reservoir section to be evaluated is located. Typically, a well will have at least 1 core well, and most typically 2-5 core wells. The core well samples are typically taken along the depth of the core well, and different core well samples may correspond to different depths.
Calculating weights by coring a well sample may include the following steps.
Firstly, obtaining physical property data of each core well sample.
The physical property data of the core well sample comprises siliceous mineral content, carbonate content, pyrite content and total organic carbon content of the corresponding sample.
The physical property data of each core well sample can be obtained from the X-ray diffraction test data and the physical property test data of each core well sample. The X-ray diffraction test data of each coring well sample comprise the proportion (content) of mineral components such as quartz, feldspar, calcite, dolomite, pyrite, clay and the like; the physical property test data of each core well sample comprises porosity and total organic carbon content.
And secondly, acquiring an image of the rock slice of each core well sample.
In the second step, firstly, the rock slices obtained from each core well rock sample are collected, the slices are vertical slices, so that vertical streaks can be displayed, and the slices can ensure that lithological change and microcrack development characteristics can be identified after preparation (the streaks are related to the deposition process, each layer represents a stratum formed in a geological age, generally cracks develop along the layer, and the cracks are easy to observe by cutting in the direction vertical to the layer).
Alternatively, slices from individual samples from at least one entire core well may be selected for weight analysis, wherein a slice may be taken from one core well sample.
And secondly, observing the vertical thin slice (any side) by adopting a single-polarization microscope, and performing screenshot on the images under the scale of 500 mu m uniformly to obtain the images of the corresponding rock slices.
In order to facilitate the identification of the number of the striae and the unification of the pixel mean value reference, the image sizes of the rock slices are uniform, and may be unified to 2400 pixels × 1800 pixels, for example, the major axis is the bedding direction (extending direction of a single rock stratum), and the minor axis is the rock vertical evolution direction. The image size may be preset under the sheet mirror.
And thirdly, determining the weight of the physical property data relative to the bedding development strength based on the physical property data of each core well sample and the image of the rock slice of each core well sample.
The third step may include the following steps.
Step 1, determining the bedding development strength of each core well sample based on the image of the rock slice of each core well sample.
The bedding development strength of the core well sample can characterize the bedding development strength of the shale gas reservoir at the depth of the core well sample.
Step 1 may include the following steps.
And 11, determining the number of the striation layers of each core well sample based on the image of the rock lamella of each core well sample.
Step 11 may include the following steps.
And 11a, meshing the images of the rock slices of the core well samples according to the target mesh size.
The mesh division is to reduce the amount of calculation and improve the calculation efficiency. The single grid size may be 60 pixels by 60 pixels, equivalent in size to 0.125mm by 0.125mm, with the major and minor axes of each image comprising 40 and 30 grids, respectively, for an image of 2400 pixels by 1800 pixels.
And 11b, graying the image of the rock slice of each core well sample.
In order to reduce the influence of microcracks, the microcracks identified under the mirror may be wiped off before the image of the rock slice of each cored well sample is grayed out, and the microcracks are filled with a mineral tone in contact with the original crack wall surface after wiping off. And then graying the image.
And 11c, counting the number of the unit grids with the pixel values larger than the target threshold value in each row of unit grids after graying, wherein the arrangement direction of the unit grids in the same row is parallel to the extension direction of a single rock stratum.
And when the number of the unit grids with the pixel values larger than the target threshold value in two adjacent rows is respectively larger than and smaller than the target number (in two adjacent rows, the number of the unit grids with the pixel values larger than the target threshold value in one row is larger than the target number, and the number of the unit grids with the pixel values larger than the target threshold value in the other row is smaller than the target number), adding one to the number of the striae of the corresponding sample.
Step 11c comprises:
first, the grayed image is converted into a black-and-white image.
The conversion mode may include: setting 128 pixels as the target threshold, equating a grid with more than 128 pixels after graying to a grid with 255 (white) pixels, and equating a grid with less than 128 pixels after graying to a grid with 0 (black), an image with only black and white grids can be acquired.
In the grayed image, the pixel value of the bright white grid is 255, the pixel value of the black grid is 0, and the pixel value of the gray grid is an intermediate value between 0 and 255. In comparison with the target threshold, the average value of all pixels included in the unit grid may be compared with the target threshold, or any one pixel may be acquired from the unit grid and the acquired pixel value may be compared with the target threshold. Preferably, any one of the pixels is taken from the unit grid and the obtained pixel value is compared with the target threshold value, which can improve the calculation efficiency.
Second, the number of black grids in each line of the black-and-white image is determined.
When the number of the long-axis black grids in a certain row is more than 20, the row is determined to be black carbon and clay layers, otherwise, the row is a white brittle layer. When the number of the long-axis black grids in the adjacent rows is larger than 20, the black carbon and clay layers are continuously deposited according to the number of the rows, and the black carbon and clay layers are white brittle layers on the contrary. When two adjacent rows of long-axis black grids are respectively larger than 20 and smaller than 20, the number of read lines is increased by 1 layer according to a deposition environment change surface between the two rows, so that the number of lines in the longitudinal unit thickness (0.125mm multiplied by 30 which is 3.75cm) of the picture is obtained and is a uniform unit, and finally the number of lines in the standard unit thickness (1m) is integrated as a result.
And step 12, determining the pixel mean value of the grayed image of the rock slice of each core well sample based on the image of the rock slice of each core well sample.
The pixel mean value is the pixel mean value, the higher the pixel mean value is, the higher the bright white layer proportion is, namely, the content of the brittle components is high, and the lower the pixel mean value is, the higher the black layer proportion is, namely, the content of the carbonaceous and clay components is high. Alternatively, after the image is grayed (step 11b), the pixel values of each unit grid in the whole image are read, and the average value is taken as the pixel average value of the corresponding sample of the image.
And step 13, calculating the bedding development strength of each core well sample based on the number of the striations of each core well sample and the pixel mean value of the grayed rock slice image of each core well sample.
And multiplying the number of the striations of each core well sample by the pixel mean value of the grayed image of the rock slice of the corresponding core well sample to obtain the bedding development strength of each core well sample.
And 2, determining the weight of the physical property data relative to the bedding development strength based on the bedding development strength of each core well sample and the physical property data of each core well sample.
And pre-establishing a weight relation between different physical property data and the bedding development strength so as to represent the bedding development strength. The weight relationship is shown in equation (1).
LoPo＝a1fSi+b1fCa+c1fPy+d1fToc+f1 (1)
In the formula:
Lo-number of layers, layers/m;
Po-pixel average, 0-255;
fSi、fCa、fPy、fToc-siliceous (quartz + feldspar), carbonate (calcite + dolomite), pyrite, total organic carbon content,%;
a1、b1、c1、d1、f1-a weighting factor related to the intensity of the bedding development.
The data of all the coring well rock slices collected by the well zone are expressed according to the equation (1), and the weight a is carried out by combining the equation (1) of each coring well rock slice1、b1、c1、d1、f1And (4) calculating.
And fourthly, determining the weight of the physical property data relative to the bedding joint development strength based on the bedding development strength of the shale gas storage layer section to be evaluated, the physical property data of each core well sample and the image of the rock slice of each core well sample.
The fourth step may include the following steps.
And step A, determining the bedding seam development strength of each core well sample based on the image of the rock slice of each core well sample.
The bedding crack development strength comprises the number of cracks and the width of the cracks, and the step A can comprise the following steps: the number of fracture lines and fracture width for each of the core well samples is determined based on the image of the rock slice for each of the core well samples.
The vertical thin section of the rock was observed under a single-polarization microscope, the number of cracks per unit thickness (0.125mm × 30 ═ 3.75cm) and the width of the cracks were observed and counted in the picture of the untreated microcracks (which were not erased) (the cracks were clearly visible under the microscope due to the large magnification of the microscope), and the number of cracks was integrated into the number of cracks per standard unit thickness (1m) as a result. Optionally, the width of the crack under the mirror is 20-50 μm at most.
The number of fractures and fracture width for each cored well sample may be read in advance and set into a computer.
And step B, determining the weight of the physical property data relative to the bedding seam development strength based on the bedding development strength of the shale gas storage layer section to be evaluated, the bedding seam development strength of each core well sample and the physical property data of each core well sample.
And (3) pre-establishing a weight relation among different physical property data, bedding development strength and bedding seam development strength to characterize the bedding seam development strength, wherein the weight relation is shown as an equation (2).
FoWo＝a2fSi+b2fCa+c2fPy+d2fToc+e2LoPo+f2 (2)
In the formula:
Fo-number of cracks, strips/m;
Wo-crack width, mm;
Lo-number of layers, layers/m;
Po-pixel average, 0-255;
fSi、fCa、fPy、fToc-siliceous (quartz + feldspar), carbonate (calcite + dolomite), pyrite, total organic carbon content,%;
a2、b2、c2、d2、f2-a weighting factor related to the development intensity of the lamellar seams.
The data of all the coring well rock slices collected by the well zone are expressed according to equation (2), and the weight a is carried out by combining the equation (2) of each coring well rock slice2、b2、c2、d2F 2.
And (3) respectively substituting the weight of the physical property data relative to the bedding development strength and the physical property data of the shale gas storage layer section to be evaluated into the equation (1), and calculating to obtain the bedding development strength of the shale gas storage layer section to be evaluated.
And 204, calculating the bedding joint development strength of the shale gas storage layer section to be evaluated based on the weight of the physical property data relative to the bedding joint development strength and the physical property data of the shale gas storage layer section to be evaluated.
And (3) respectively substituting the weight of the physical property data relative to the bedding joint development strength and the physical property data of the shale gas storage layer section to be evaluated into the equation (2), and calculating to obtain the bedding joint development strength of the shale gas storage layer section to be evaluated.
And step 205, calculating the natural weak surface index of the shale gas storage interval to be evaluated based on the bedding development strength and the bedding joint development strength of the shale gas storage interval to be evaluated.
Step 205 may include the following steps.
Step 205a, determining a bedding development strength index based on the bedding development strength of the shale gas storage interval to be evaluated.
The index of the bedding development strength is calculated according to the following equation (3).
In the formula:
Ln-intensity of bedding development, dimensionless;
LoPobedding development strength of shale gas reservoir section to be evaluated, (L)oPo)max、(LoPo)min-maximum and minimum values of the bedding development strength, layer/m, calculated on the basis of the images of the individual rock slices.
And step 205b, determining a bedding joint development strength index based on the bedding joint development strength of the shale gas storage layer section to be evaluated.
The bedding seam development strength index is calculated according to the following equation (4).
In the formula:
Fnthe development strength of the bedding joint is dimensionless;
FoWothe bedding joint development strength of the shale gas reservoir section to be evaluated, (F)oWo)max、(FoWo)min-maximum and minimum values of bedding joint development strength, bar mm/m, calculated on the basis of the images of the individual rock slices.
And step 205c, calculating the natural weak surface index of the shale gas reservoir section to be evaluated based on the bedding development strength index and the bedding joint development strength.
The natural weak plane index can be calculated according to the following equation (5).
In the formula:
Innatural weak plane index, dimensionless.
And step 206, optimizing the fracturing scheme of the shale gas storage interval to be evaluated based on the natural weak surface index of the shale gas storage interval to be evaluated.
Step 206 may include: when the natural weak surface index is lower than the first target value, enhancing the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated; when the development strength of the natural weak surface is higher than a first target value and lower than a second target value, maintaining the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated, wherein the first target value is smaller than the second target value; and when the development strength of the natural weak surface is higher than a second target value, weakening the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated.
In addition, when the natural weak surface index is equal to the first target value, the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated can be enhanced, and the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated can also be kept; when the development strength of the natural weak surface is equal to the second target value, the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated can be kept, and the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated can also be weakened.
Optionally, the fracturing schemes of the shale gas reservoir interval to be evaluated refer to the main fracturing processes of shallow (<3500m) and deep (>3500m) shale gas reservoir. The fracturing main processes of the shale gas reservoir with the shallow layer (<3500m) and the deep layer (>3500m) can be obtained from a fracturing design book of a single well which is subjected to fracturing construction nearby the well.
Illustratively, the first target value is 0.4 and the second target value is 0.6, when In<When the pressure is 0.4, the development strength of the natural weak face of the shale gas reservoir section is low, the fracturing fluid liquid consumption amount can be increased, the number of perforation holes can be increased, and the temporary blocking steering technology can be implemented to promote the maximum steering expansion of the water conservancy cracks on the basis of the main fracturing process of the shale gas reservoir corresponding to the depth of the natural weak face, so that a large reservoir reconstruction volume is formed; when 0.4<In<When the pressure is 0.6, the development degree of the natural weak surface is high, and the shale gas reservoir fracturing main body process corresponding to the depth can be matched to realize more sufficient transformation; when I isn>0.6 time, it means that the natural weak face has too high development degree, and the fluid loss behavior of the fracturing fluid to the weak face is increasedThe construction risk is increased, at the moment, the number of perforation holes can be reduced on the basis of the shale gas reservoir fracturing main body process corresponding to the depth, the high-concentration sand carrying of glue liquid and the low-concentration sand carrying of slickwater are pumped in stages, effective supporting and effective crack forming are respectively realized, more fracturing liquid is used for forming new cracks, the liquid efficiency is increased, and sand blocking and pressure abnormal risks are reduced.
The shale gas reservoir fracturing main process corresponding to the depth of the shale gas reservoir section to be evaluated is taken as a shallow layer (<3500m) shale gas reservoir fracturing main process for example.
The main process of the shallow shale gas reservoir comprises the following steps: the length of the single section is 60-80 m, the number of clusters is 3 clusters, and the amount of single-section fracturing fluid is 1800m3Mainly low-viscosity slick water, the amount of single-section sand is 120t, wherein 70/140-mesh quartz sand accounts for 36t, 40/70-mesh ceramsite accounts for 84t, and the construction discharge amount is 12-14 m3And/min, wherein the number of the single-section perforation holes is 36-40.
When I isn<And when the first target value (such as 0.4) is obtained, the development strength of the natural weak surface of the shale gas reservoir section is low, and the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated is enhanced. Illustratively, the amount of large fracturing fluid is increased to 2000m3Increasing the number of the perforation holes to 40-48 holes, and implementing a temporary blocking steering technology to promote the maximum steering expansion of the water conservancy cracks, so as to form a larger reservoir transformation volume.
When the first target value (e.g. 0.4)<In<And when the second target value (such as 0.6) is higher, the development degree of the natural weak face is high, and the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated is maintained. Illustratively, fracturing is performed according to shallow or deep shale gas reservoir bulk processes.
When I isn>And when the second target value (such as 0.6) is higher than the natural weak plane development degree, weakening the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated. Illustratively, the number of the perforation holes is reduced to 30, the high-concentration sand carrying of the glue solution and the low-concentration sand carrying of the slickwater are mixed and pumped in stages to realize effective support and effective crack creation respectively, more fracturing fluids are guaranteed to be used for creating new cracks, the liquid efficiency is increased, sand blockage and abnormal pressure wind are reducedAnd (5) risking.
Step 205 and step 206 realize that the fracturing scheme of the shale gas storage interval to be evaluated is optimized based on the bedding development strength and the bedding crack development strength of the shale gas storage interval to be evaluated.
An example application scenario of the method for optimizing the fracturing of the shale gas reservoir provided by the embodiment is described below.
Step 1, taking a well A as an example and taking the well A as a coring well, acquiring X-ray diffraction test data and physical property test data, and comprising the following steps: 1) the mineral components such as quartz, feldspar, calcite, dolomite, pyrite, clay and the like account for the proportion; 2) total organic carbon content; and collecting the rock slices.
And 2, sorting the slices collected by the well A, carrying out high-density sampling and grinding on longitudinal slices, carrying out 2400 pixel × 1800 pixel image size processing, dividing 60 pixel × 60 pixel unit grids, smearing micro cracks, carrying out full-mirror image gray processing, reading unit grid pixel values, judging a threshold value, dividing all the grids into black and white, finally identifying a pattern layer changing picture, reading the number of the pattern layers, and converting the number into the number of the pattern layers with the thickness of 1 m. The process is shown in fig. 3 (the middle part of fig. 3 is grayed out to form the boundary of the stripe layer by the dotted line in the grayed image).
And 3, performing weight calculation on the data of all the coring well rock slices collected in the research area, wherein the weight formula of the well zone where the well A is located is shown as an equation (1). Optionally, a is calculated1、b1、c1、d1、f1Respectively as follows: 0.48, 2.07, 0.12, 0.32, 42.
And 4, taking the well A as an example, identifying the number of the microcracks and the crack width of the thin sheet cored and ground by the well A, and converting the number of the microcracks into 1m of thickness, wherein the crack width is 20-50 μm under a mirror.
Step 5, characterizing the development strength of the bedding joints, and calculating the weight of the data of all the core well rock slices collected in the research area according to the equation (2), and optionally calculating the obtained a2、b2、c2、d2、f2Comprises the following steps: 0.34, 1.41, 0.07, 2.2, 0.32, 55.
And 6, establishing a natural weak surface evaluation index, and optimizing fracturing process parameters. Taking the well B as an example, the well B is a production well in a well zone of the well A, and the physical property parameters are shown in the following table 1.
TABLE 1
| Fracturing sub-section (segment number) | Carbonate rock (%) | Siliceous mineral (%) | Pyrite (%) | TOC(％) |
| 1 | 11.2 | 58.6 | 0.2 | 2.5 |
| 2 | 12.6 | 52.6 | 0.4 | 3.2 |
| 3 | 12.8 | 53.4 | 0.6 | 4.4 |
| 4 | 13.5 | 51.5 | 0.5 | 3.5 |
| 5 | 14.6 | 65.5 | 0.4 | 3.4 |
| 6 | 15.4 | 61.6 | 0.2 | 3.2 |
| 7 | 16.1 | 61.4 | 0.3 | 2.8 |
| 8 | 13.1 | 58.4 | 0.3 | 3.6 |
| 9 | 12.8 | 62.3 | 0.5 | 2.7 |
| 10 | 12.9 | 66.5 | 0.5 | 2.5 |
| 11 | 11.2 | 62.5 | 0.6 | 3.1 |
| 12 | 10.5 | 63.5 | 0.4 | 2.8 |
| 13 | 9.7 | 61.5 | 0.4 | 3.4 |
| 14 | 8.2 | 54.4 | 0.3 | 4.1 |
| 15 | 7.7 | 56.2 | 0.5 | 4.6 |
| 16 | 6.5 | 57.8 | 0.6 | 4.2 |
| 17 | 4.3 | 56.3 | 0.4 | 4.5 |
| 18 | 5.7 | 55.4 | 0.5 | 5.2 |
| 19 | 6.2 | 61.6 | 0.6 | 4.8 |
| 20 | 6.1 | 60.5 | 0.5 | 5.4 |
| 21 | 6.4 | 57.7 | 0.4 | 6.1 |
| 22 | 6.1 | 56.9 | 0.5 | 6.3 |
| 23 | 7.3 | 57.6 | 0.6 | 5.7 |
| 24 | 6.4 | 55.5 | 0.6 | 5.9 |
| 25 | 6.2 | 56.2 | 0.6 | 5.6 |
Combining equations (1) - (5), the weights obtained from well a are applied to well B to obtain the calculation parameters, see table 2 below.
TABLE 2
Calculating and comparing according to each shale gas reservoir section of the well B, wherein for 1-13 sections, the natural weak surface evaluation index is 0.4-0.6, so that construction is carried out by using fracturing design process parameters; in 14-25 sections, the evaluation index of the natural weak surface is less than 0.4, so the development degree of the natural weak surface is low, and the liquid amount of the fracturing fluid needs to be increased, the number of perforation holes needs to be increased, and the temporary blocking steering technology needs to be implemented to promote the maximum steering expansion of the hydraulic fracture.
In the embodiment, the bedding development strength and the bedding joint development strength of the shale gas storage interval to be evaluated are determined, the bedding development strength and the bedding joint development strength can represent the development strength of a natural weak surface, and the natural weak surface is an important characteristic of geology, so that the geological understanding of complex geological conditions (high stress, deep burying and the like) can be accurately realized; and optimizing the fracturing scheme of the shale gas reservoir section to be evaluated based on the bedding development strength and the bedding joint development strength of the shale gas reservoir section to be evaluated, so that the fracturing operation efficiency and the yield increasing effect are improved.
In addition, experimental analysis data and logging-while-drilling interpretation data obtained based on conventional interpretation means respect objective rules, summarize the interrelation and weight coefficient between various factors related to the formation and development of the natural weak surface and the development scale of the natural weak surface, establish a non-equivalent linear regression equation, realize the evaluation and characterization of the development strength of the natural weak surface, provide optimization basis for the fracturing scheme and design of the shale gas horizontal well, improve the original real-time adjustment means based on artificial experience, accurately identify the development scale of the natural weak surface near the shaft before fracturing, and enable the optimization of the fracturing scheme design to have quantitative effect.
Fig. 4 is a structural block diagram of a fracturing optimization device for a shale gas reservoir provided by an embodiment of the present disclosure, and referring to fig. 4, the fracturing optimization device includes: a first determining module 401, a second determining module 402 and an evaluating module 403.
The first determination module 401 is configured to determine that the bedding development of the shale gas storage interval to be evaluated is strong.
And a second determining module 402, configured to determine the development strength of the bedding joint of the shale gas reservoir interval to be evaluated.
The evaluation module 403 is configured to optimize a fracturing scheme of the shale gas storage interval to be evaluated based on the bedding development strength and the bedding fracture development strength of the shale gas storage interval to be evaluated.
Optionally, the first determining module 401 is configured to obtain a weight of the physical property data relative to the intensity of the bedding development; acquiring physical property data of a shale gas storage layer section to be evaluated; and calculating the bedding development strength of the shale gas storage layer section to be evaluated based on the weight of the physical property data relative to the bedding development strength and the physical property data of the shale gas storage layer section to be evaluated.
Optionally, the first determining module 401 is configured to obtain an image of a rock slice of each coring well sample, where the coring well sample is a rock sample in a coring well of a well region where the shale gas reservoir section to be evaluated is located; determining the bedding development strength of each core well sample based on the image of the rock slice of each core well sample; obtaining physical property data of each core well sample; determining a weight of the physical property data relative to the bedding development strength based on the bedding development strength of each cored well sample and the physical property data of each cored well sample.
Optionally, the first determining module 401 is configured to determine the number of streaks for each of the core well samples based on the image of the rock slice for each of the core well samples; determining the pixel mean value of the grayed images of the rock slices of the various core well samples based on the images of the rock slices of the various core well samples; and calculating the bedding development strength of each core well sample based on the number of the striae of each core well sample and the pixel mean value of the grayed image of the rock slice of each core well sample.
Optionally, the first determining module 401 is configured to perform meshing on the image of the rock slice of each cored well sample according to the target mesh size; graying the image of the rock slice of each core well sample; counting the number of unit grids with pixel values larger than a target threshold value in each row of unit grids after graying, wherein the unit grids in the same row are parallel to the extending direction of a single rock stratum; and when the number of the unit grids with the pixel values of two adjacent rows larger than the target threshold is respectively larger than and smaller than the target number, adding one to the number of the thread layers of the corresponding sample.
Optionally, the second determining module 402 is configured to obtain a weight of the physical property data relative to a development intensity of the bedding joint; acquiring physical property data of a shale gas storage layer section to be evaluated; and calculating the bedding seam development strength of the shale gas storage layer section to be evaluated based on the bedding development strength of the shale gas storage layer section to be evaluated, the weight of the physical property data relative to the bedding seam development strength and the physical property data of the shale gas storage layer section to be evaluated.
Optionally, the second determining module 402 is configured to obtain an image of a rock slice of each coring well sample, where the coring well sample is a rock sample in a coring well of a well region where the shale gas reservoir section to be evaluated is located; determining the bedding joint development strength of each core well sample based on the image of the rock slice of each core well sample; obtaining physical property data of each core well sample; and determining the weight of the physical property data relative to the bedding joint development strength based on the bedding development strength of the shale gas storage interval to be evaluated, the bedding joint development strength of each core well sample and the physical property data of each core well sample.
Optionally, the second determining module 402 is configured to determine a fracture number and a fracture width for each of the core well samples based on the image of the rock slice of each of the core well samples; and calculating the bedding crack development strength of each core well sample based on the number and width of the cracks of each core well sample.
Optionally, the evaluation module 403 is configured to calculate a natural weak surface index of the shale gas storage interval to be evaluated based on the bedding development intensity index and the bedding joint development intensity of the shale gas storage interval to be evaluated; when the natural weak surface index is lower than the first target value, enhancing the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated; when the development strength of the natural weak surface is higher than a first target value and lower than a second target value, maintaining the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated, wherein the first target value is smaller than the second target value; and when the development strength of the natural weak surface is higher than a second target value, weakening the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated.
Fig. 5 shows a block diagram of a fracture optimization device for a shale gas reservoir according to an exemplary embodiment of the present invention. The fracturing optimization device 300 for shale gas reservoirs may be a computer.
The fracture optimization apparatus 300 includes a Central Processing Unit (CPU)301, a system memory 304 including a Random Access Memory (RAM)302 and a Read Only Memory (ROM)303, and a system bus 305 connecting the system memory 304 and the central processing unit 301. The fracture optimization apparatus 300 also includes a basic input/output system (I/O system) 306 to facilitate the transfer of information between the various devices within the computer, and a mass storage device 307 for storing an operating system 313, application programs 314, and other program modules 315.
The basic input/output system 306 comprises a display 308 for displaying information and an input device 309, such as a mouse, keyboard, etc., for a user to input information. Wherein a display 308 and an input device 309 are connected to the central processing unit 301 through an input output controller 310 connected to the system bus 305. The basic input/output system 306 may also include an input/output controller 310 for receiving and processing input from a number of other devices, such as a keyboard, mouse, or electronic stylus. Similarly, an input-output controller 310 may also provide output to a display screen, a printer, or other type of output device.
The mass storage device 307 is connected to the central processing unit 301 through a mass storage controller (not shown) connected to the system bus 305. The mass storage device 307 and its associated computer-readable media provide non-volatile storage for the fracture optimization apparatus 300. That is, the mass storage device 307 may include a computer-readable medium (not shown) such as a hard disk or CD-ROM drive.
Without loss of generality, computer readable media may comprise computer storage media and communication media. Computer storage 13 media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer storage media includes RAM, ROM, EPROM, EEPROM, flash memory or other solid state memory technology, CD-ROM, DVD, or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices. Of course, those skilled in the art will appreciate that computer storage media is not limited to the foregoing. The system memory 304 and mass storage device 307 described above may be collectively referred to as memory.
According to various embodiments of the invention, the fracture optimization device 300 may also be operated by a remote computer connected to a network via a network, such as the internet. That is, the fracture optimization apparatus 300 may be connected to the network 312 through the network interface unit 311 connected to the system bus 305, or may be connected to other types of networks or remote computer systems (not shown) using the network interface unit 311.
The memory further includes one or more programs, and the one or more programs are stored in the memory and configured to be executed by the CPU. The one or more programs include instructions for performing the fracture optimization methods provided by embodiments of the present invention.
It should be noted that: when the fracturing optimization device for the shale gas reservoir provided by the embodiment is used for fracturing optimization of the shale gas reservoir, the division of the functional modules is only used for illustration, and in practical application, the functions can be distributed by different functional modules according to needs, that is, the internal structure of the equipment is divided into different functional modules, so that all or part of the functions described above can be completed. In addition, the fracturing optimization device for the shale gas reservoir provided by the embodiment and the fracturing optimization method for the shale gas reservoir belong to the same concept, and specific implementation processes are detailed in the method embodiment and are not repeated herein.
It will be understood by those skilled in the art that all or part of the steps for implementing the above embodiments may be implemented by hardware, or may be implemented by a program instructing relevant hardware, where the program may be stored in a computer-readable storage medium, and the above-mentioned storage medium may be a read-only memory, a magnetic disk or an optical disk, etc.
The above description is intended to be exemplary only and not to limit the present disclosure, and any modification, equivalent replacement, or improvement made without departing from the spirit and scope of the present disclosure is to be considered as the same as the present disclosure.
Claims (11)
1. A fracturing optimization method for a shale gas reservoir is characterized by comprising the following steps:
determining the bedding development strength of a shale gas storage layer section to be evaluated, wherein the bedding development strength refers to the degree of formation, development and existence of a layered structure generated by the change of rocks along the vertical direction along with the change of time;
determining the bedding joint development strength of the shale gas storage layer section to be evaluated, wherein the bedding joint development strength refers to the degree of formation, development and existence of various layer seams formed due to uneven rock structures along with time change;
and optimizing the fracturing scheme of the shale gas storage interval to be evaluated based on the bedding development strength and the bedding seam development strength of the shale gas storage interval to be evaluated.
2. The fracturing optimization method according to claim 1, wherein the determining the bedding development strength of the shale gas reservoir interval to be evaluated comprises:
acquiring the weight of physical property data relative to the layering development strength, wherein the physical property data refers to data related to the appearance and the property of an object;
acquiring physical property data of the shale gas storage layer section to be evaluated;
and calculating the bedding development strength of the shale gas storage interval to be evaluated based on the weight of the physical data relative to the bedding development strength and the physical data of the shale gas storage interval to be evaluated.
3. The method of claim 2, wherein obtaining the weight of the physical property data relative to the strength of bedding development comprises:
acquiring an image of a rock slice of each coring well sample, wherein the coring well sample is a rock sample in a coring well of a well zone where the shale gas reservoir section to be evaluated is located;
determining the bedding development strength of each core well sample based on the image of the rock slice of each core well sample;
obtaining physical property data of each core well sample;
determining a weight of the physical property data relative to the bedding development strength based on the bedding development strength of each cored well sample and the physical property data of each cored well sample.
4. The fracture optimization method of claim 3, wherein determining the bedding development strength of each of the core well samples based on the image of the rock slice of each of the core well samples comprises:
determining the number of streaks of each of the core well samples based on the image of the rock slice of each of the core well samples;
determining the pixel mean value of the grayed images of the rock slices of the various core well samples based on the images of the rock slices of the various core well samples;
and calculating the bedding development strength of each core well sample based on the number of the striae of each core well sample and the pixel mean value of the grayed image of the rock slice of each core well sample.
5. The fracture optimization method of claim 4, wherein determining the number of streaks for each of the core well samples based on the image of the rock slice for each of the core well samples comprises:
meshing the images of the rock slices of the core well samples according to the target mesh size;
graying the image of the rock slice of each core well sample;
counting the number of unit grids with pixel values larger than a target threshold value in each row of unit grids after graying, wherein the unit grids in the same row are parallel to the extending direction of a single rock stratum;
and when the number of the unit grids with the pixel values of two adjacent rows larger than the target threshold is respectively larger than and smaller than the target number, adding one to the number of the thread layers of the corresponding sample.
6. The fracturing optimization method according to claim 1, wherein the determining the development strength of the bedding joint of the shale gas reservoir interval to be evaluated comprises:
acquiring the weight of the physical property data relative to the development strength of the bedding seams;
acquiring physical property data of the shale gas storage layer section to be evaluated;
and calculating the bedding seam development strength of the shale gas storage interval to be evaluated based on the bedding development strength of the shale gas storage interval to be evaluated, the weight of the physical property data relative to the bedding seam development strength and the physical property data of the shale gas storage interval to be evaluated.
7. The method of claim 6, wherein obtaining the weight of the physical property data relative to the development strength of the bedding joint comprises:
acquiring an image of a rock slice of each coring well sample, wherein the coring well sample is a rock sample in a coring well of a well zone where the shale gas reservoir section to be evaluated is located;
determining the bedding joint development strength of each core well sample based on the image of the rock slice of each core well sample;
obtaining physical property data of each core well sample;
and determining the weight of the physical property data relative to the bedding joint development strength based on the bedding development strength of the shale gas storage interval to be evaluated, the bedding joint development strength of each core well sample and the physical property data of each core well sample.
8. The fracturing optimization method according to claim 1, wherein the optimizing the fracturing plan of the shale gas reservoir section to be evaluated based on the bedding development strength and the bedding fracture development strength of the shale gas reservoir section to be evaluated comprises:
calculating a natural weak surface index of the shale gas storage layer section to be evaluated based on the bedding development intensity index and the bedding seam development intensity of the shale gas storage layer section to be evaluated;
when the natural weak surface index is lower than a first target value, enhancing the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated;
when the natural weak plane development strength is higher than the first target value and lower than a second target value, maintaining the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated, wherein the first target value is smaller than the second target value;
and when the development strength of the natural weak plane is higher than the second target value, weakening the fracturing degree corresponding to the fracturing scheme of the shale gas reservoir section to be evaluated.
9. A fracturing optimization device for shale gas reservoirs, comprising:
the first determination module is used for determining the bedding development strength of the shale gas storage layer section to be evaluated, wherein the bedding development strength refers to the degree of the formation, development and existence of a layered structure generated by the change of rock along the vertical direction along with the change of time;
the second determination module is used for determining the bedding joint development strength of the shale gas storage layer section to be evaluated, wherein the bedding joint development strength refers to the degree of formation, development and existence of various layer internal joints formed due to uneven rock structure along with time change;
and the evaluation module is used for optimizing the fracturing scheme of the shale gas storage interval to be evaluated based on the bedding development strength and the bedding crack development strength of the shale gas storage interval to be evaluated.
10. A fracturing optimization device for shale gas reservoirs, comprising: a memory, a processor and a computer program stored in the memory and executable on the processor, the processor being configured to implement the method of fracture optimization of a shale gas reservoir as claimed in any one of claims 1 to 8 when executing the computer program.
11. A computer storage medium having stored therein at least one instruction, the instruction being loaded and executed by a processor to implement the method of fracture optimization of a shale gas reservoir as claimed in any one of claims 1 to 8.
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