CN115354991B - A Method for Optimizing Favorable Fracturing Intervals in Coal Measure Gas Reservoirs - Google Patents

Abstract

The invention provides a coal-based gas reservoir favorable fracturing interval optimization method, which comprises the following steps of: drawing lithology superposition mode plates; determining the optimal fracturing position corresponding to each lithology stacking mode and sequencing the lithology stacking modes in order from good to bad; identifying lithology on the single well, comparing lithology combinations formed by the lithology combinations with lithology stacking modes according to the sequence from top to bottom by taking the gray/sandstone as a reference to determine actual lithology stacking modes corresponding to each gray/sandstone, screening out effective lithology stacking modes from the actual lithology stacking modes, and finally determining the optimal fracturing position of the single well according to the effective lithology stacking modes. According to the method provided by the invention, the lithology on a single well is finely depicted, so that the determination of the fracturing position is more accurate; on the other hand, a reproducible, clear-structured and well-purposed fracturing interval optimization method for the multi-lithology combined coal-based reservoir is formed, so that the time and money cost are saved.

Description

A Method for Optimizing Favorable Fracturing Intervals in Coal Measure Gas Reservoirs

technical field

The invention relates to the field of geological technology, in particular to a method for optimizing favorable fracturing intervals of coal-measure gas reservoirs.

Background technique

Coalbed methane, tight sandstone gas and shale gas all have development potential in coal-measure gas reservoirs, and the co-exploration and production technology of "two gases" or even "three gases" is an inevitable requirement for economical and efficient development of coal-measure gas reservoirs. However, due to the tight structure and low permeability of coal-measure gas reservoirs, they need to be developed by means of fracturing. However, coal-measure reservoirs are frequently interbedded with various lithologies, resulting in large vertical changes in the mechanical properties of reservoir rocks, making it difficult to select intervals for fracturing.

Early scholars believed that coalbed methane was the main gas source of coal-measure natural gas, and mostly directly used coal seams as fracturing intervals. In recent years, some scholars have constructed a multi-lithology symbiosis model for coal-measure reservoirs for the goal of multi-gas co-production in coal-measure reservoirs, and based on this basis, based on corresponding engineering constraints, excluded layers that are difficult to undergo engineering fracturing. Finally determine the coal-measure gas reservoir fracturing target interval. However, the current method is too simple to describe the symbiotic combination mode of coal-measure reservoirs, and cannot systematically characterize the lithology superimposition relationship of complex coal-measure reservoirs, resulting in inaccurate selection of fracturing intervals in coal-measure gas reservoirs. At the same time, due to the differences between different wells, the current method cannot form a set of fracturing interval optimization system applicable to the whole region, and needs to be analyzed well by well, which will consume a lot of time and financial resources.

Contents of the invention

The purpose of the present invention is to solve the above-mentioned defects in the prior art, and provide a method for optimizing favorable fracturing intervals of coal-measure gas reservoirs.

A method for optimizing favorable fracturing intervals of coal-measure gas reservoirs, comprising the following steps:

Step 100: drawing the corresponding lithological overlay pattern charts of all drilling wells in the research area;

Step 200: Determine the optimal fracturing position corresponding to each lithology superposition mode, and sort the development potential of each lithology superposition mode in order from good to poor;

Step 300: Identify the lithology of a single well in the research area one by one, so as to determine the quantity of ash/sandstone in the single well and the location of each ash/sandstone; the lithology includes: coal rock, mud shale , gray/sandstone;

Step 400: Based on each limestone/sandstone benchmark, determine the actual lithology combination 1 of the limestone/sandstone and its adjacent lithology composition above, and the actual lithology combination 2 of its adjacent lithology composition below it;

Step 500: Compare the actual lithology combination 1 and the actual lithology combination 2 with the preset lithology superposition modes one by one, and determine all the actual lithology superposition modes corresponding to each limestone/sandstone;

Step 600: Determine all effective actual lithological overlay modes corresponding to each limestone/sandstone;

Step 700: Determine the optimal lithology superposition mode corresponding to each lime/sandstone from all effective actual lithology superposition modes;

Step 800: Determine the optimal fracturing position corresponding to each lime/sandstone according to the optimal lithology superposition pattern corresponding to each lime/sandstone;

Step 900: Use the optimal fracturing position corresponding to each limestone/sandstone as the optimal fracturing position for the entire single well.

Further, in the above-mentioned method for optimizing coal-measure gas reservoir favorable fracturing intervals, step 100 includes the following steps:

Step 110: Obtain the logging data, mud logging data, and drilling coring data corresponding to all wells in the study area;

Step 120: Determine the lithology of the research area according to the logging data, mud logging data, and drilling coring data corresponding to all drilling; the lithology includes: lime/sandstone, mud shale, coal;

Step 130: Classify the lime/sandstone, mud shale, and coal into reservoir lithology and non-reservoir lithology according to electrical characteristics, lithological characteristics, physical characteristics and gas-bearing characteristics;

Step 140: Determine the thickness corresponding to the non-reservoir lithology;

Step 150: When the thickness corresponding to the non-reservoir lithology is greater than 3 meters, classify the non-reservoir lithology as an interlayer; if the thickness corresponding to the non-reservoir lithology is less than 3 meters Next, the non-reservoir lithology is divided into interlayers;

Step 160: Taking all the lithologies between the two interlayers as a lithology combination, drawing a lithology superimposition pattern map corresponding to the lithology combination.

Further, in the method for optimizing favorable fracturing intervals of coal-measure gas reservoirs as described above, the lithology superimposition pattern chart corresponding to all drilling includes 6 kinds of lithology superposition patterns, and the 6 kinds of lithology superposition patterns are arranged according to the The order from top to bottom is:

Mode 1: gray/sandstone, mud shale, coal;

Mode 2: coal, ash/sandstone, mud shale;

Mode 3: mud shale, coal, ash/sandstone;

Mode 4: coal, mud shale, gray/sandstone;

Mode 5: gray/sandstone, coal, mud shale;

Mode 6: mud shale, gray/sandstone, coal.

Furthermore, the method for optimizing favorable fracturing intervals of coal-measure gas reservoirs as described above is sorted according to the order of fracturing positions from good to bad:

Mode 5 > Mode 3 > Mode 1 > Mode 4 > Mode 6 > Mode 2.

Further, in the above-mentioned method for optimizing the favorable fracturing interval of the coal-measure gas reservoir, the step 600 specifically includes the following steps:

Step 610: Determine the distance between the optimal fracturing position and the coal seam for all actual lithological superposition modes corresponding to each limestone/sandstone;

Step 620: When the distance is greater than a certain preset value, the lithology superposition mode is valid; otherwise, the lithology superposition mode is invalid;

Step 630: Screen out effective lithology superimposition patterns from all the actual lithology superposition patterns as all effective actual lithology superposition patterns corresponding to each limestone/sandstone.

Further, in the above-mentioned method for optimizing coal-measure gas reservoir favorable fracturing intervals, the step 200 includes:

According to the gas-bearing distribution characteristics, the fracturing ranking of various lithologies, and the mineral distribution characteristics of lithology combinations, the optimal fracturing position corresponding to each lithology superposition mode is determined.

Further, in the above-mentioned method for optimizing coal-measure gas reservoir favorable fracturing intervals, the fracturing ranking of various lithologies includes:

According to the elastic modulus and Poisson's ratio corresponding to each type of lithology, the fracturing properties of each type of rock are arranged in order from high to low, and the following is obtained:

The fracturing properties of lime/sandstone>the fracturing properties of mud shale>the fracturing properties of coal rocks.

Beneficial effect:

The method for optimizing favorable fracturing intervals of coal-measure gas reservoirs provided by the present invention, on the one hand, determines the optimal fracturing pattern of each lithology superposition mode according to the corresponding lithology superposition mode charts of all drillings in the entire research area. The location of fractures and the optimal lithology superposition mode, and then the lithology combination on the single well is compared with the lithology superposition mode chart one by one, so as to determine the optimal lithology superposition mode on the single well, and According to the optimal lithology superposition mode on a single well, the optimal fracturing position on a single well is determined. This method makes a fine description of the lithology on a single well, so that the determination of the fracturing position is more accurate; on the other hand , the present invention directly locks the optimal fracturing position through various lithological superposition modes, so that the optimal fracturing position in the entire region becomes the choice of lithological superposition mode on a single well, and this method forms a multi-lithology combination A reproducible, well-organized, and purposeful approach to fracturing interval optimization for coal-measure reservoirs, saving time and money.

Description of drawings

Fig. 1 is the flow chart of the method for optimizing the favorable fracturing intervals of coal-measure gas reservoirs provided by the present invention;

Fig. 2 is the intersection curve diagram of non-reservoir lithological single-layer thickness and frequency of occurrence;

Fig. 3 is the intersection curve of non-reservoir lithological single-layer thickness and total hydrocarbon content;

Fig. 4 is a schematic diagram of the layout of lithology superimposition mode of different lithology combinations;

Fig. 5 is the intersection diagram of shale brittle mineral content and distance from limestone/sandstone;

Fig. 6 is the intersection diagram of clay mineral content of mud shale and the distance from the coal seam;

Fig. 7 is a diagram of the lithology superposition mode in the mud-sand/ash-coal lithology combination;

Fig. 8 is a cross-sectional view of the lithology superposition mode of the lithology combination in Well X1.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention are clearly and completely described below. Apparently, the described embodiments are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

The invention mainly solves the problem of optimal fracturing position of coal-measure reservoirs with diverse lithology, thin single layer and complex superimposed relationship. According to the characteristics of coal-measure reservoirs, by clarifying the properties of each lithologic reservoir and non-reservoir in the area, the non-reservoir is divided into interlayer and interlayer according to the thickness limit; on this basis, all lithology between interlayers Treat it as a lithology combination and conduct statistical analysis on the lithology superposition relationship of all lithology combinations in the area, and draw the lithology superposition mode chart of the lithology combination in the whole area.

On the basis of the above, the in-depth analysis of the gas-bearing distribution characteristics of the lithology combination, combined with the test results of the mechanical properties of each lithology in the area and the distribution of minerals in the lithology combination, determined the gas under various lithology superposition modes. The optimal fracturing location; considering the gas distribution characteristics of the lithologic combination and the gas flow law after fracturing, a method for judging the validity of the lithological superimposition modes in the region is given and the advantages and disadvantages of various lithological superposition modes are analyzed. Finally, based on the sandstone/limestone with a thickness of less than 3 meters in a single well, an effective lithology stacking model is constructed from top to bottom, and the optimal lithology stacking model is selected The corresponding optimal fracturing position of the setting model is used as the last fracturing interval.

The method provided by the present invention is further elaborated below:

Fig. 1 is a flowchart of a method for optimizing favorable fracturing intervals of coal-measure gas reservoirs provided by the present invention, the method comprising the following steps:

Step 100: Draw the corresponding lithological overlay pattern charts for all wells drilled in the study area.

Wherein, the drawing of described lithology superimposition model plate comprises the following steps:

Step 110: Obtain well logging data, mud logging data, and drilling coring data corresponding to all wells in the study area.

Step 120: Determine the lithology of the study area according to the logging data, mud logging data, and drilling coring data corresponding to all drilling; the lithology includes: lime/sandstone, mud shale, coal;

Step 130: Classify the lime/sandstone, mud shale and coal into reservoir lithology and non-reservoir lithology according to electrical properties, lithology, physical properties and gas-bearing characteristics.

Specifically, obtain the corresponding electrical characteristics, lithological characteristics, physical characteristics and gas-bearing characteristics of the lime/sandstone, mud shale, and coal, and compare these characteristics with relevant national reservoir and non-reservoir standards , so as to determine whether lime/sandstone, mud shale, and coal are reservoirs or non-reservoirs. Among them, gray/sandstone is a non-reservoir, and coal and mud shale are reservoirs.

Step 140: Determine the thickness corresponding to the non-reservoir lithology.

Step 150: When the thickness corresponding to the non-reservoir lithology is greater than 3 meters, classify the non-reservoir lithology as an interlayer; if the thickness corresponding to the non-reservoir lithology is less than 3 meters Next, the non-reservoir lithology is divided into interbeds.

It should be noted that due to the poor physical properties of the non-reservoir, the flow of gas in it is difficult, but as long as it is not too thick, the gas can still pass through; if it is too thick, it cannot pass through, so the non-reservoir that is too thick Divided into interlayers, non-reservoir divisions with small thickness are called interlayers. Moreover, all lithologies between two interlayers are regarded as a lithology combination, and the interlayer and other lithologies together constitute a lithology combination. The determination of whether a non-reservoir layer is an interlayer or an interlayer is based on a thickness limit. The method for determining this limit is: counting the frequency of non-reservoir (sand/ash) single-layer thickness in the study area (Fig. 2), It can be seen that the frequency has an obvious turning point at 3 meters, indicating that most non-reservoir lithology thicknesses are less than 3 meters. The total hydrocarbon content is a parameter that can characterize the gas-bearing property. It is found that the thickness of the non-reservoir lithology is more than 3 meters, and the total hydrocarbon content is at a low level (the lithology combination is not connected and is separated by sandstone/limestone). Therefore, 3 meters is determined as the thickness limit of non-reservoir lithology as interlayer or interlayer.

Step 160: Taking all the lithologies between the two interlayers as a lithology combination, drawing a lithology superimposition pattern map corresponding to the lithology combination.

Specifically, all lithologies in the two interlayers are regarded as a lithology combination, and the lithology superimposition relationship of each lithology combination in the work area is counted, and the lithology superposition relationship of the lithology combinations that can cover all situations in the work area is drawn. Set up the pattern layout. As shown in Figure 4, the lithology superimposition pattern charts corresponding to all drilling wells include 6 lithology superposition patterns, and the 6 lithology superposition patterns are in order of lithology from top to bottom, respectively: Mode 1: Gray/sandstone, mud shale, coal; mode 2: coal, gray/sandstone, mud shale; mode 3: mud shale, coal, gray/sandstone; mode 4: coal, mud shale, gray/sandstone; mode 5: gray/sandstone, coal, mud shale; mode 6: mud shale, gray/sandstone, coal.

Step 200: Determine the optimal fracturing position corresponding to each lithology superposition mode, and rank the development potential of each lithology superposition mode in order from good to poor.

Specifically, the determination of the optimal fracturing position for each lithology superposition mode is based on three factors: (1) the distribution characteristics of gas-bearing properties of lithology combinations (gas-bearing properties are high near coal seams); Sorting of fracturing properties of rocks; (3) Mineral distribution characteristics of lithological assemblages. Combined to determine the optimal fracturing location for each lithologic overlay pattern.

At the same time, rock mechanical properties were measured for different lithologies in the study area. Based on parameters such as elastic modulus and Poisson's ratio, it is considered that the fracturing properties in the study area are ranked as limestone/sandstone fracturing >mud shale fracturing > Coal rock fracability. At the same time, considering the distribution characteristics of minerals based on the lithological combination as a whole, it is found that the shale intervals near the limestone/sandstone layer and far away from the coal seam have high brittle mineral content and better brittleness, which is conducive to subsequent fracturing (Fig. 5, Fig. 6). Accordingly, as shown in Figure 7, when the lime/sandstone and mud shale are distributed on both sides of the coal seam, the reservoir where the lime/sandstone is located is selected as the optimal fracturing location (model 3 and model 5 in the figure ). If the lime/sandstone and mud shale are distributed on the same side of the coal seam, the junction of lime/sandstone and mud shale is selected as the optimal fracturing location (as shown in model 1, model 2, model 4, and model 6). In the case of mode 3 and mode 5, since the gas flows upward, the development potential of coal-measure gas in mode 5 is relatively higher. In Mode 1, Mode 2, Mode 4, and Mode 6, although sand/limestone has the smallest gas supply capacity, it is more conducive to subsequent fracturing when sand/limestone is in the upper part of coal seam or mud shale. Based on the above analysis, the best crack initiation horizons corresponding to the coal-sand/lime-mud coexistence lithology superposition model are: model 1 and model 2 suggest that cracks should be initiated at the top of sand/limestone and mud shale in the lithological combination section , Model 4 and Model 6 suggest that the cracks should be initiated at the bottom of sand/limestone and mud shale in the lithological combination section, and models 3 and 5 should be selected to initiate cracks in the middle of the lithological combination sand/limestone.

The gas-bearing distribution characteristics of the lithological combination in the study area are studied, and it is found that coalbed methane is the main gas source of coal-measure reservoirs, so the closer to the coal seam, the higher the gas-bearing property. However, considering the distribution characteristics of minerals in the overall lithology combination, the comparison of the gas-bearing properties of different lithological intervals in a single well in the study area shows that although the gas-bearing properties are high near the coal seam, it cannot be directly fractured in the coal seam, because the coal seam can be Low fracturing. Considering the influence of seepage at the same time, during the fracturing process, the gas will diffuse upward along the fractures, so the fracturing interval (sand/limestone) above the main gas supply interval (coal seam/mud shale) is more conducive to follow-up fracture. Therefore, the order of development potential of each lithologic superimposition model from good to poor is: model 5> model 3> model 1> model 4> model 6> model 2.

Step 300: Identify the lithology of a single well in the research area one by one, so as to determine the quantity of ash/sandstone in the single well and the location of each ash/sandstone; the lithology includes: coal rock, mud shale , Ash/Sandstone.

As shown in Figure 8, the lithology of a single well is identified from top to bottom, wherein the lithology combination corresponding to the section lithology is the result of the lithology identification of the single well. It can be seen from the figure that there are four gray/sandstone layers, namely: gray/sandstone layer ①, gray/sandstone layer ②, gray/sandstone layer ③, and gray/sandstone layer ④. The location of each lime/sandstone and its adjacent lithologies can be determined from the depth of a single well.

Step 400: Based on each lime/sandstone benchmark, determine the actual lithological combination 1 of the lime/sandstone and its adjacent lithological composition above, and the actual lithological combination 2 of its adjacent lithological composition below it.

Step 500: Compare the actual lithology combination 1 and the actual lithology combination 2 with the preset lithology superposition modes one by one, and determine all the actual lithology superposition modes corresponding to each limestone/sandstone.

It can be seen from Fig. 8 that the lime/sandstone layer ① and its adjacent lithology constitute the actual lithology combination 1, and the lithology adjacent to its lower layer constitute the actual lithology combination 2. Comparing the actual lithology combination 1 with all lithology superposition modes (mode 1-mode 6), it is found that the actual lithology combination 1 is consistent with the lithology combination of mode 6; the actual lithology combination 2 is compared with all Comparing the lithological superimposition modes (mode 1-mode 6) one by one, it is found that the actual lithological combination 2 is consistent with the lithological combination of mode 5. It can be seen that the actual lithological superposition corresponding to the lime/sandstone layer ① There are two modes, namely: Mode 6 and Mode 5. In the same way, determine all the actual lithological superposition modes corresponding to the lime/sandstone layer ②, and finally determine that there is one actual lithological superposition mode corresponding to the lime/sandstone layer ②, which is mode 6. There are two actual lithological superposition modes corresponding to the gray/sandstone layer ③, namely: Mode 1 and Mode 2. There are three actual lithological superposition modes corresponding to the lime/sandstone layer ④, namely: mode 4, mode 5 and mode 6.

Step 600: Determine all valid actual lithological overlay patterns corresponding to each limestone/sandstone.

The following describes in detail how to determine whether the lithology overlay mode is valid:

Firstly, determine the distance from the optimal fracturing position to the coal seam for all actual lithological superposition modes corresponding to each limestone/sandstone. Secondly, when the distance is greater than a certain preset value, the lithology overlay mode is valid; otherwise, the overlay mode is invalid; finally, effective lithology is selected from all the actual lithology overlay modes Overlay patterns are all valid actual lithological overlay patterns corresponding to each gray/sandstone.

Specifically, since the optimal fracturing position in various lithological superimposition modes is close to the coal seam, and the coal seam is the worst in fracturing, the thin layer to which the optimal fracturing position belongs will make the fracture directly to the softer The extension of coal seam is not conducive to the formation of complex fracture network and the embedding of proppant in coal seam will greatly reduce the effectiveness of fractures. Therefore, the optimal fracturing position should be kept at a certain distance from the coal seam but not too far away. Based on the gas distribution law of lithologic combination, fracture extension law and fracturing properties of each lithology, it is considered that the optimal fracturing position and coal seam distance should be within 1-2m in each lithologic superimposition mode, and the distance less than 1m does not constitute a fracture. Effective lithology overlay mode. Assuming that in the lithology superposition mode corresponding to the sandstone layer ④, the optimal fracturing position corresponding to mode 5 is less than 1m away from the coal seam, then delete mode 5, then only mode 4 remains in the actual lithology superposition mode corresponding to the sandstone layer ④ and mode 6.

Step 700: Determine the optimal lithology superposition mode corresponding to each lime/sandstone from all the effective actual lithology superposition modes, and the optimal lithology superposition mode is the rock with the best fracturing position. sexual overlay mode.

Step 800: Determine the optimal fracturing position corresponding to each lime/sandstone according to the optimal lithology superposition pattern corresponding to each lime/sandstone;

Step 900: Use the optimal fracturing position corresponding to each limestone/sandstone as the optimal fracturing position for the entire single well.

Specifically, taking Fig. 8 as an example, after deleting mode 5 in the actual lithology superposition mode corresponding to the gray/sandstone layer ④, mode 4 and mode 6 remain, and the fracturing positions according to the lithology superposition mode range from good to poor The order is: Mode 5>Mode 3>Mode 1>Mode 4>Mode 6>Mode 2, then Mode 4 and Mode 6 are preferred to Mode 4, so the fracturing position corresponding to the gray/sandstone layer ④ is the optimal fracturing position corresponding to Mode 4. crack location. In the same way, the actual lithological superimposition mode corresponding to the gray/sandstone layer ① is preferred to mode 5 from mode 6 and mode 5, so the optimal fracturing position corresponding to the gray/sandstone layer ① is the optimal fracturing position corresponding to mode 5 ; The actual lithological superposition mode corresponding to the gray/sandstone layer ② is: mode 6, but mode 6 is the inferior mode, therefore, the gray/sandstone layer ② has no optimal fracturing position. The actual lithological superposition mode corresponding to the gray/sandstone layer ③ is: Mode 1. Then, in the end, there are three optimal fracturing positions for a single well corresponding to Figure 8, from top to bottom: gray/sandstone layer ① corresponding to model 5, gray/sandstone layer ③ corresponding to model 1, gray/sandstone Layer ④ corresponds to mode 4 (at this time, it is assumed that the fracturing position of mode 5 is less than 1m away from the coal seam). It can be obtained directly, and finally, it can be determined that sand ①, sand ③ and sand ④ are the most favorable for fracturing in this single well lithology combination.

The method provided by the present invention is described in detail below, and the method specifically includes the following steps:

(1) Acquire well logging data, mud logging data, and drilling coring data corresponding to all wells drilled in the target research area;

(2) Determine the lithology of the study area according to the logging data, mud logging data, and drilling coring data corresponding to all drilling; the lithology includes: lime/sandstone, mud shale, coal;

(3) According to electrical characteristics, lithological characteristics, physical characteristics and gas-bearing characteristics, the lime/sandstone, mud shale, and coal are divided into reservoir lithology and non-reservoir lithology;

(4) Determine the thickness of the reservoir corresponding to the non-reservoir lithology; when the thickness is greater than 3 meters, divide the reservoir as a barrier; when the thickness is less than 3 meters, dividing the reservoir into interlayers;

(5) taking all the lithology between the two interlayers as a lithology combination, drawing the corresponding lithology superimposition pattern plate of the lithology combination;

(6) Determine the optimal fracturing position corresponding to each lithology superposition mode according to the gas-bearing distribution characteristics, fracturing ranking of various lithologies, and mineral distribution characteristics of lithology combinations; The development potential of configuration modes is ranked from best to worst;

(7) On the single well, the lithology on the single well is identified one by one, thereby determining the quantity of lime/sandstone on the single well and the position of each lime/sandstone; the lithology includes: coal rock, mud sheet rock, lime/sandstone;

(8) With each lime/sandstone benchmark, determine the actual lithology combination 1 of said lime/sandstone and its upper adjacent lithology formation, and the actual lithology combination 2 of its adjacent lithology formation below;

(9) comparing the actual lithology combination 1 and the actual lithology combination 2 with the preset lithology superimposition patterns one by one, to determine all the actual lithology superposition patterns corresponding to each limestone/sandstone;

(10) Determine whether all lithology superimposition patterns corresponding to each limestone/sandstone are valid; when the optimal fracturing position is more than 1 meter away from the coal reservoir, the lithology superposition pattern is valid; otherwise, delete the corresponding The lithology overlay pattern plate;

(11) On the premise that the lithology superimposition pattern chart is valid, determine the optimal lithology superposition pattern corresponding to each lime/sandstone according to the order of the lithology superposition patterns;

(12) Determine the optimal fracturing position corresponding to each lime/sandstone according to the optimal lithology superposition mode corresponding to each lime/sandstone;

(13) Take the optimal fracturing position corresponding to each lime/sandstone as the optimal fracturing position for the entire single well.

Experimental example:

Using the method provided by the present invention to carry out example analysis on a single well. Taking Well X1 in the study area as an example, Fig. 5 shows the lithology superimposition model diagram of mud-sand-coal lithology combination in Well X1. A total of 4 sets of sandstone layers with a thickness of less than 3m developed in the mud-sand-coal lithology combination of Well X1. Comparing with the lithology superposition pattern diagram in Fig. 1, there are 5 lithology superposition patterns. Among them, sand ① corresponds to the two lithological superposition models of Model 5 and Model 6; sand ② only corresponds to Model 6; sand ③ corresponds to the two lithological superposition models of Model 1 and Model 2; sand ④ corresponds to Model 4, Model 5 and Model 6 Three kinds of lithology superposition modes. It is judged that each lithology superimposition mode satisfies the effectiveness. According to the ranking of the advantages and disadvantages of the lithology superposition modes, the final sand ① is preferred to mode 5, the sand ③ is preferred to mode 1, and the sand ④ is preferred to mode 5. To sum up, in these four sets of sandstones, the lithology superposition mode corresponding to sand ①, sand ③ and sand ④ is the dominant mode, and the one corresponding to sand ② is the inferior mode. Therefore, the mud-sand-coal lithology combination in Well X1 It is most favorable to choose sand ①, sand ③ and sand ④ for fracturing.

The present invention describes in detail the lithology superimposition mode map in the region for coal-measure reservoirs, deepens the understanding of coal-measure reservoirs; clarifies the optimal fracturing position of each mode, and provides a single well lithology superposition mode The optimal solution is to select the fracturing location based on the analysis results of the single well lithology superposition mode, which greatly reduces the difficulty of implementing optimal fracturing intervals and is applicable to the entire area, which greatly saves time and money costs.

For the coal-measure reservoirs with diverse lithology, thin single layer and complex superposition relationship, the lithology superposition relationship is comprehensively described and the relevant lithology superposition model chart is drawn.

Through the in-depth analysis of the gas-bearing distribution characteristics of lithological combinations, combined with the test results of mechanical properties of each lithology in the area and the distribution of minerals in lithological combinations, the optimal fracturing positions under various lithological superposition modes are determined. Finally, the method of judging the effectiveness of lithology superimposition mode and the ranking of advantages and disadvantages are given, and the selection method of lithology superposition mode on a single well is provided, which reduces the difficulty of implementing optimal fracturing intervals and is applicable to the entire region.

Aiming at the characteristics of frequent alternation and co-occurrence of multiple lithologies in coal-measure reservoirs, the present invention establishes a lithology superposition mode, deeply analyzes and directly locks the optimal fracturing position under various lithology superposition modes, and divides the Preference is given to switching to the selection of the best lithology overlay mode on a single well. Finally, the basis for selection of effective lithology superposition modes is provided and the pros and cons of each lithology superposition mode are sorted. It can be directly applied to a single well and is applicable to the entire area, which brings great convenience to the optimization of fracturing intervals.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be Modifications are made to the technical solutions described in the foregoing embodiments, or equivalent replacements are made to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims (5)

1. A coal-measure gas reservoir favorable fracturing interval optimization method, is characterized in that, comprises the following steps: Step 100: drawing the corresponding lithological overlay pattern charts of all drilling wells in the research area; Step 200: Determine the optimal fracturing position corresponding to each lithology superposition mode, and sort the development potential of each lithology superposition mode in order from good to poor; Step 300: Identify the lithology of a single well in the research area one by one, so as to determine the quantity of ash/sandstone in the single well and the location of each ash/sandstone; the lithology includes: coal rock, mud shale , gray/sandstone; Step 400: Based on each limestone/sandstone benchmark, determine the actual lithology combination 1 of the limestone/sandstone and its adjacent lithology composition above, and the actual lithology combination 2 of its adjacent lithology composition below it; Step 500: Compare the actual lithology combination 1 and the actual lithology combination 2 with the preset lithology superposition modes one by one, and determine all the actual lithology superposition modes corresponding to each limestone/sandstone; Step 600: Determine all effective actual lithological overlay modes corresponding to each limestone/sandstone; Step 700: Determine the optimal lithology superposition mode corresponding to each lime/sandstone from all effective actual lithology superposition modes; Step 800: Determine the optimal fracturing position corresponding to each lime/sandstone according to the optimal lithology superposition pattern corresponding to each lime/sandstone; Step 900: Use the optimal fracturing position corresponding to each limestone/sandstone as the optimal fracturing position for the entire single well; Step 100 includes the following steps: Step 110: Obtain the logging data, mud logging data, and drilling coring data corresponding to all wells in the study area; Step 120: Determine the lithology of the research area according to the logging data, mud logging data, and drilling coring data corresponding to all drilling; the lithology includes: lime/sandstone, mud shale, coal; Step 130: Classify the lime/sandstone, mud shale, and coal into reservoir lithology and non-reservoir lithology according to electrical characteristics, lithological characteristics, physical characteristics and gas-bearing characteristics; Step 140: Determine the thickness corresponding to the non-reservoir lithology; Step 150: When the thickness corresponding to the non-reservoir lithology is greater than 3 meters, classify the non-reservoir lithology as an interlayer; if the thickness corresponding to the non-reservoir lithology is less than 3 meters Next, the non-reservoir lithology is divided into interlayers; Step 160: Taking all the lithologies between the two interlayers as a lithology combination, drawing the corresponding lithology superimposition mode chart of the lithology combination; The lithology superimposition pattern chart corresponding to all drilling wells includes 6 kinds of lithology superposition patterns, and the 6 kinds of lithology superposition patterns are according to the order of lithology from top to bottom, respectively: Mode 1: gray/sandstone, mud shale, coal; Mode 2: coal, ash/sandstone, mud shale; Mode 3: mud shale, coal, ash/sandstone; Mode 4: coal, mud shale, gray/sandstone; Mode 5: gray/sandstone, coal, mud shale; Mode 6: mud shale, gray/sandstone, coal. 2. The method for optimizing favorable fracturing intervals of coal-measure gas reservoirs according to claim 1, characterized in that, the fracturing positions are sorted according to the sequence from good to bad: Mode 5 > Mode 3 > Mode 1 > Mode 4 > Mode 6 > Mode 2. 3. The method for optimizing favorable fracturing intervals of coal-measure gas reservoirs according to claim 1, wherein the step 600 specifically comprises the following steps: Step 610: Determine the distance between the optimal fracturing position and the coal seam for all actual lithological superposition modes corresponding to each limestone/sandstone; Step 620: When the distance is greater than a certain preset value, the lithology superposition mode is valid; otherwise, the lithology superposition mode is invalid; Step 630: Screen out effective lithology superposition patterns from all the actual lithology superposition patterns as all valid actual lithology superposition patterns corresponding to each limestone/sandstone. 4. The method for optimizing favorable fracturing intervals of coal-measure gas reservoirs according to claim 1, characterized in that, the step 200 comprises: According to the gas-bearing distribution characteristics, the fracturing ranking of various lithologies, and the mineral distribution characteristics of lithology combinations, the optimal fracturing position corresponding to each lithology superposition mode is determined. 5. The method for optimizing favorable fracturing intervals of coal-measure gas reservoirs according to claim 4, wherein the fracturing order of the various lithologies comprises: According to the elastic modulus and Poisson's ratio corresponding to each type of lithology, the fracturing properties of each type of rock are arranged in order from high to low, and the following is obtained: The fracturing properties of lime/sandstone>the fracturing properties of mud shale>the fracturing properties of coal rocks.