A method for selecting a perforation position of a coal seam roof horizontal well for improving a coal seam fracturing reconstruction volume

Abstract

The present application relates to a kind of fracturing perforation position selection method, belong to a kind of coalbed gas horizontal well development technical field, specifically relates to a kind of coal seam roof horizontal well fracturing perforation position selection method.The present application provides new method and train of thought for the optimal perforation position of coal seam roof horizontal well, can reduce the problem of pump pressure being too high, sanding difficulty in reservoir reconstruction process, improve the reconstruction efficiency of coal seam.

Description

TECHNICAL FIELD

[0001] The application relates to a fracturing and perforating position selection method, and belongs to the technical field of coalbed methane horizontal well development. BACKGROUND

[0002] China's coal basins have experienced multiple tectonic actions, resulting in strong reformation of coal seam structures, and extensive development of broken soft coal seams, low pore-forming rate of horizontal well drilling, poor fracturing reconstruction effect, and serious influence on coalbed methane development effect. In order to improve the pore-forming rate and coal body reconstruction rate of the broken soft coal seam horizontal well, in 2012, the Xi'an Research Institute of China Coal Technology and Engineering Group Co., Ltd. proposed a coalbed methane development technology for the coal seam roof horizontal well in view of the characteristics of the broken soft coal seam of the No. 8 coal seam in the Luling minefield. After reservoir reconstruction, the daily maximum gas production of the horizontal well group was 10358m 3 , and good results were achieved. As of 2021, a total of about 10 broken soft low-permeability coal seam roof horizontal wells have been constructed nationwide, and the development technology is in the stage of continuous improvement. How to improve the extraction efficiency of the roof horizontal well and improve the coalbed methane extraction technology is a theoretical and technical problem that needs to be solved. Before the fracturing of the coalbed methane horizontal well, the perforating charge is used to communicate the production casing and the formation, and to establish a channel for the fracturing fluid to enter the formation. The different perforating positions of the horizontal well are directly related to the extension direction and distance of the subsequent hydraulic fractures. In the past, the perforating position of the coal seam roof horizontal well was selected according to the relative position of the horizontal section wellbore trajectory and the coal seam, the cementing quality of the horizontal section, and the principle of uniform perforation. In the actual production process, due to improper selection of the perforating position, the high elastic modulus and low Poisson's ratio of the mudstone and the swelling of the clay mineral when water is added, the pump pressure increases, sand addition is difficult, and other phenomena occur, which affect the reconstruction effect of the horizontal well. Based on this, the relative distance data of the horizontal section of the coal seam roof horizontal well and the coal seam, the mud content data of each point of the horizontal section, the cementing quality data of the horizontal section, and the data of the perforating position distance from the production casing coupling are used to establish a comprehensive evaluation index curve of the fracturing and perforating position of the coal seam roof horizontal well, so as to solve the problem of insufficient theoretical basis for the selection of the perforating position of the coal seam roof horizontal well. Through the application, the volume of the fracturing and reconstruction of the coal seam roof horizontal well is improved, the coalbed methane recovery rate is improved, and a new method for selecting the perforating position of the coal seam roof horizontal well is provided. SUMMARY

[0003] In order to solve the problem of the imperfect theory basis for optimizing the fracturing perforation position of the coal seam roof horizontal well in the prior art, the present application provides a method for selecting the perforation position of the coal seam roof horizontal well before fracturing reconstruction, which uses the relative distance data of the horizontal section of the horizontal well and the coal seam, the shale content data of the horizontal section, the cementing quality data, and the perforation position distance from the casing collar data to establish a comprehensive evaluation index prediction model for the fracturing perforation position of the coal seam roof horizontal well, and designs the fracturing perforation position of the horizontal well according to the comprehensive evaluation index curve of the perforation position and in combination with the fracturing section number.

[0004] To solve the above problems, the scheme of the present application is:

[0005] A method for selecting the perforation position of the coal seam roof horizontal well for improving the fracturing reconstruction volume of the coal seam, which comprises the following steps:

[0006] Step 1, collecting the logging data of the horizontal section of the coal seam roof horizontal well while drilling and the cementing quality logging data;

[0007] Step 2, collecting the logging data of the borehole (the well with a distance of less than 500 m from the horizontal well) around the coal seam roof horizontal well and the coal seam depth data;

[0008] Step 3, using the natural gamma data of the coal seam roof horizontal well while drilling, comparing with the natural gamma curves of the target coal seam and the top and bottom plates of the coal seam gas well near the horizontal well, further combining the contour map of the target coal seam bottom plate and the drilling cuttings identification data to determine the relative distance between the wellbore trajectory of the roof horizontal well and the target coal seam, and performing normalization processing;

[0009] Step 4, using the natural gamma data of the coal seam roof horizontal well while drilling, calculating the shale content size of each point of the horizontal section, and performing normalization processing;

[0010] Step 5, according to the cementing quality detection result of the coal seam roof horizontal well, performing value assignment processing on the cementing quality interpretation result of the horizontal section.

[0011] Step 6, checking the magnetic positioning data in the logging interpretation data of the coal seam roof horizontal well, and according to the production casing collar data of the horizontal section of the coal seam roof horizontal well, performing value assignment on the safety degree of the distance from the production casing collar during the fracturing reconstruction of each point of the horizontal section.

[0012] Step 7, according to the comprehensive evaluation index prediction model for the fracturing perforation of the coal seam roof horizontal well, calculating the comprehensive evaluation index of the perforation position of each point of the horizontal section of the coal seam roof horizontal well;

[0013] Step 8, drawing the curve of the well depth and the comprehensive evaluation index of the perforation position of the horizontal well through the calculated comprehensive evaluation index of the fracturing perforation position of the horizontal section of the coal seam roof horizontal well;

[0014] Step 9: Based on the comprehensive evaluation index curve of the perforation location and the number of fracturing sections in the horizontal well, design the perforation locations of each fracturing section in the horizontal well of the coal seam roof.

[0015] In step 4, since each drill pipe is approximately 10m long during horizontal well drilling, and the wellbore orientation and inclination are adjusted after each drill pipe is drilled, the data prediction point spacing for the perforation location comprehensive evaluation index curve is set to 10m to facilitate subsequent data calculation and application. The ideal formula for calculating the clay content is as follows:

[0016] SH = (GR - GR) min ) / (GR max -GR min (1)

[0017] V sh =(2 GCUR·SH -1) / (2 GCUR -1)×100% (2)

[0018] In the formula: GR is the response value of the natural gamma curve, API; GR min The natural gamma logging response values ​​(API and GR) are for pure sandstone near the target coal seam. max API is the natural gamma logging response value of pure mudstone near the target coal seam; SH is the relative value of the natural gamma curve, dimensionless; V sh , represents the mud content of the formation, in percent; GCUR is an empirical coefficient, dimensionless.

[0019] In step 5, C represents the quality of cementing near the perforated section of the horizontal well in the coal seam roof. Within 20m to the left and right of the perforation location in the horizontal section of the horizontal well, if the cementing quality is unsatisfactory, a value of 0 is assigned; if the cementing quality is satisfactory, a value of 1 is assigned.

[0020] In step 6, D represents the safety level of the distance between the perforation location of the horizontal well in the coal seam roof and the casing coupling. When the distance between the perforation location of the horizontal well in the coal seam roof and the production casing coupling is less than 1m, the value is 0; when the distance between the perforation location and the production casing coupling is greater than 1m, the value is 1.

[0021] In step 7, the comprehensive evaluation index prediction model for the location of the horizontal well fracturing perforation in the coal seam roof considers the following four aspects: (1) the mud content of the perforation section of the horizontal well: the mechanical properties of the high elastic modulus and low Poisson's ratio of mudstone and the effect of the expansion of clay minerals when exposed to water will lead to increased pump pressure and difficulty in sand addition when fracturing in the mudstone section; (2) the distance of the well trajectory from the coal seam: if the perforation location is far from the coal seam, the hydraulic fracture is not easy to extend from the roof to the coal seam; (3) the quality of cementing: when the cementing quality near the perforation section is poor, the hydraulic fracture is easy to extend from the channel between the casing and the annulus, increasing the risk of cross-contamination between fracturing sections and affecting the effect of horizontal well fracturing; (4) the distance of the perforation section from the production casing coupling: if the distance of the perforation section from the production casing coupling is less than 1m, during the fracturing process, the mechanical strength near the casing coupling is weaker than other places, making it easy to deform and break, affecting the subsequent stability of the wellbore; the calculation formula of the comprehensive evaluation index for the location of the horizontal well fracturing perforation is as follows:

[0022] Y = A + B + C + D (3)

[0023] in,

[0024] In the formula: d is the distance from the coal seam to the horizontal section of the horizontal well trajectory on the roof of the coal seam, in meters; d min The minimum distance (m) from the horizontal section of the wellbore trajectory to the coal seam in a horizontal section of a coal seam roof well; d max The maximum distance (in meters) between the horizontal section of the horizontal wellbore trajectory and the coal seam.

[0025]

[0026] In the formula: V sh Formation clay content, %; V shmin V represents the minimum clay content (%) in the formation near the wellbore trajectory of a horizontal section of a horizontal well in the coal seam roof. shmax The maximum value of clay content in the formation near the wellbore trajectory of the horizontal section of the coal seam roof horizontal well, %.

[0027] Step 9: Based on the principle of uniform perforation fracturing in the horizontal section of a horizontal well in the coal seam roof, and combined with the comprehensive evaluation index curve of the perforation location drawn in Step 8, select the perforation location in the horizontal section of the horizontal well. The selection of the perforation location follows... n represents the number of data points used to plot the comprehensive evaluation index curve of the horizontal well depth and perforation location in the coal seam roof; Y represents the comprehensive evaluation index of the fracturing perforation location in the horizontal well in the coal seam roof. n This represents the comprehensive evaluation index of the location of fracturing perforations in horizontal wells on the top of a coal seam when the number of data points is n.

[0028] Therefore, compared with the prior art, the present invention has the following advantages: the present invention provides a new method and idea for the optimal fracturing perforation location of horizontal wells in the roof of coal seams, which can reduce the problems of excessive pump pressure and difficulty in adding sand during reservoir stimulation, and improve the efficiency of coal seam stimulation. Attached Figure Description

[0029] Figure 1 This is a flowchart of the invention.

[0030] Figure 2 This is a schematic diagram of the horizontal shaft structure of a coal seam roof.

[0031] Figure 3 This is a well logging interpretation profile of a coalbed methane well near the X-05H horizontal well (within 500m).

[0032] Figure 4 This is the comprehensive evaluation index curve of the fracturing and perforation location in the horizontal section of the X-05H horizontal well.

[0033] Figure 5 This is the fracturing construction curve for the first stage of the X-05H horizontal well.

[0034] Figure 6 This is the fracturing operation curve for the second stage of the X-05H horizontal well.

[0035] Figure 7 This is the fracturing construction curve for the third stage of the X-05H horizontal well.

[0036] Figure 8 This is the fracturing operation curve for the fourth stage of the X-05H horizontal well.

[0037] Figure 9 This is the fracturing operation curve for the fifth stage of the X-05H horizontal well.

[0038] Figure 10 This is the fracturing operation curve for the 6th stage of the X-05H horizontal well.

[0039] Figure 11 This is the fracturing operation curve for the 7th stage of the X-05H horizontal well.

[0040] Figure 12 This is the fracturing operation curve for the 8th stage of the X-05H horizontal well.

[0041] Figure 13 This is a schematic diagram of the gas production of the X-05 horizontal well group.

[0042] Figure 14 This is a schematic diagram of the gas production of the Y-01 horizontal well group. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to the embodiments.

[0044] In the No. 3 coal seam of the Shanxi X coalfield, during the fracturing and stimulation process of coalbed methane extraction via horizontal wells, the conventional perforation selection method frequently encounters difficulties in adding proppant, resulting in poor gas production in the later stages. New technologies are needed to improve the efficiency of fracturing and stimulation. The specific process is as follows:

[0045] Step 1: Collect logging-while-drilling data and cementing quality logging data for the horizontal section of the X-05H horizontal well;

[0046] Step 2: Collect logging data from boreholes surrounding the coalbed methane horizontal well (wells less than 500m from the horizontal well), as well as coal seam depth data.

[0047] Step 3: Using the natural gamma ray data from the X-05H horizontal well, compare it with the natural gamma ray curves of the No. 3 coal seam and the top and bottom plates of the nearby coalbed methane well. Figure 3 Further, by combining the contour map of the bottom plate of coal seam No. 3 and the drilling cuttings identification data, the relative distance between the horizontal well trajectory and coal seam No. 3 was determined (Table 1). Among them, the minimum distance between the horizontal section of the X-05H horizontal well trajectory and coal seam No. 3 was 0.01m, and the maximum distance between the horizontal section of the X-05H horizontal well trajectory and coal seam No. 3 was 1.53m. The distance between the horizontal section of the X-05H horizontal well trajectory and coal seam No. 3 was normalized, and the data are shown in Table 2.

[0048] Table 1. Prediction of the relative distance between the horizontal section and the coal seam in X-05H horizontal well.

[0049]

[0050]

[0051] Table 2. Normalized Relative Distances Between Horizontal Sections and Coal Seams in X-05H Horizontal Well

[0052]

[0053] Step 4: Based on the natural gamma data of the horizontal section of the X-05H horizontal well, determine the GR. min For 50 API, GR max The API value is 140, the formation age encountered by the horizontal well is Mesozoic, and the GCUR value is assigned to 2. Formulas 1 and 2 are used to calculate the clay content of the horizontal section of the X-05H horizontal well (Table 3). The minimum clay content of the formation near the wellbore trajectory of the horizontal section of the X-05H horizontal well is 1%, and the maximum clay content of the formation near the wellbore trajectory of the horizontal section is 88%. The clay content of each point in the horizontal section of the X-05H horizontal well is normalized, and the data are shown in Table 4.

[0054] Table 3 Prediction of mud content at various points in the horizontal section of X-05H horizontal well

[0055]

[0056] Table 4. Normalized treatment of clay content at various points in the horizontal section of X-05H horizontal well.

[0057]

[0058] Step 5: Review the cementing quality inspection report of the X-05H horizontal well. Based on the interpretation results of the cementing quality within 20m to the left and right of each predicted point in the horizontal section of the horizontal well, assign values ​​to the cementing quality of the predicted points (Table 5).

[0059] Table 5 Cementing Quality Assignment Table for Each Point in the Horizontal Section of X-05H Horizontal Well

[0060]

[0061]

[0062] Step 6: Review the magnetic positioning data in the X-05H logging interpretation report. Based on the coupling data of the production casing near each predicted point in the horizontal section of the horizontal well, assign values ​​to the safety level of each predicted point in the X-05H horizontal section relative to the production casing coupling (Table 6).

[0063] Table 6. Safety Values ​​for Distances from Production Casing to Various Points in the Horizontal Section of the X-05H Horizontal Well

[0064]

[0065] Step 7: Based on the normalized data of the relative distance between the horizontal section and the coal seam of the X-05H horizontal well (Table 2), the normalized data of the mud content at each point in the horizontal section (Table 4), the cementing quality assignment data at each point in the horizontal section (Table 5), and the data of the distance from the casing coupling safety at each point in the horizontal section (Table 6), the comprehensive evaluation index of the fracturing perforation location at each point in the horizontal section of the X-05H horizontal well is predicted according to Formula 3 (Table 7).

[0066] Table 7. Comprehensive Evaluation Index Prediction Table for Perforation Location Selection at Various Points in the Horizontal Section of X-05H Horizontal Well

[0067]

[0068] Step 8: Based on the calculated comprehensive evaluation index of the fracturing and perforation locations at various points in the horizontal section of the X-05H horizontal well, plot the comprehensive evaluation index curve of the fracturing and perforation locations corresponding to the depth of the horizontal section of the X-05H horizontal well. Figure 4 );

[0069] Step 9: Based on the data from each predicted point (Table 7), the average comprehensive evaluation index for selecting the perforation location is 2.56. Therefore, when selecting the optimal fracturing perforation location in the horizontal section of the X-05H horizontal well, the selection of the comprehensive evaluation index should follow the principle of 2 < Y < 2.56. Referring to the comprehensive evaluation index curve of the fracturing perforation location in the horizontal section of the X-05H horizontal well, and combining the principle of uniform perforation in the eight fracturing sections of the X-05H horizontal well, the perforation locations in each fracturing section of the X-05H horizontal well are designed. Figure 4 ).

[0070] Beneficial effects:

[0071] In 2013, a horizontal well group (X-01) was deployed in the X coalfield of Shanxi. The stable production period of the X-01 horizontal well group was 3000-4000m. 3 In 2014-2016, three sets of horizontal coalbed methane wells, X-02, X-03, and X-04, were redeployed in the mining area, with a maximum daily gas production of 1500-2000 m³ / d. 3 / d, gas production declines rapidly, and production ceases after six months. In 2017, a group of horizontal wells (X-05) was deployed in the northern part of the mining area. During reservoir fracturing of the X-05 horizontal well group, the perforation location selection method for the coal seam roof horizontal well, as demonstrated in this patent, was used to select the perforation locations for eight fracturing sections. Figure 4 The fracturing operation with sand addition proceeded smoothly. Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 , Figure 10 , Figure 11 and Figure 12 The construction pressure was maintained between 22-27 MPa, the average sand ratio was 12%, the sand addition completion rate reached 110%, and the daily gas production of the horizontal well group exceeded 10,000 m³. 3 ( Figure 13 This technology has also been applied to the Y-01 horizontal well group in the Anhui Y well field, achieving good gas production results. Figure 14 ).

Claims

1. A method for selecting the location of perforations in a horizontal well in a coal seam roof, characterized in that, include: The steps for determining the distance to the coal seam are as follows: Based on the logging-while-drilling data of the horizontal section of the horizontal well and the natural gamma data during drilling, determine the relative distance between the wellbore trajectory of the roof horizontal well and the target coal seam; Steps for calculating clay content: Calculate the clay content at each point in the horizontal section of the horizontal well using natural gamma data from the drilling of the horizontal well in the coal seam roof. Evaluation index determination steps: Based on the comprehensive evaluation index prediction model for perforation of horizontal wells in the coal seam roof, calculate the comprehensive evaluation index of the perforation location at each point in the horizontal section of the horizontal well in the roof. Evaluation curve plotting steps: Based on the comprehensive evaluation index of the perforation location at each point in the horizontal section of the horizontal well, plot the comprehensive evaluation index curve of the horizontal well depth versus the perforation location; Perforation location determination steps: Based on the comprehensive evaluation index curve of horizontal well depth and perforation location and the number of fracturing sections of the horizontal well, design the perforation locations of each fracturing section of the horizontal well in the coal seam roof; In the evaluation index determination step, a comprehensive evaluation index for horizontal well perforation location is constructed based on the following formula: Y = A + B + C + D (3) in: In the formula, V sh Formation clay content, %; V shmin V represents the minimum clay content (%) in the formation near the wellbore trajectory of a horizontal section of a horizontal well in the coal seam roof. shmax d represents the maximum clay content of the formation near the horizontal section of the wellbore trajectory of the horizontal well on the coal seam roof, in %; d represents the distance from the coal seam to the horizontal section of the wellbore trajectory, in meters. min The minimum distance (m) from the horizontal section of the wellbore trajectory to the coal seam in a horizontal section of a coal seam roof well; d max The maximum distance, in meters, is the wellbore trajectory of the horizontal section of a horizontal well on the roof of the coal seam from the coal seam. d represents the distance (in meters) from the horizontal section of the wellbore trajectory to the coal seam in the horizontal section of the coal seam roof. min The minimum distance (m) from the horizontal section of the wellbore trajectory to the coal seam in a horizontal section of a coal seam roof well; d max The maximum distance, in meters, is the wellbore trajectory of the horizontal section of a horizontal well on the roof of the coal seam from the coal seam. C represents the quality of cementing near the perforated section of the horizontal well in the coal seam roof. Within 20m to the left and right of the perforation location in the horizontal section of the horizontal well, if the cementing quality is unsatisfactory, a value of 0 is assigned; if the cementing quality is satisfactory, a value of 1 is assigned. D represents the safety level of the distance between the perforation location of the horizontal well in the coal seam roof and the casing coupling. When the distance between the perforation location of the horizontal well in the coal seam roof and the production casing coupling is less than 1m, the value is 0; when the distance between the perforation location and the production casing coupling is greater than 1m, the value is 1. In the step of determining the perforation location, the perforation location is selected according to... n represents the number of data points on the comprehensive evaluation index curve of horizontal well depth and perforation location; Y represents the comprehensive evaluation index of horizontal well perforation location. n The evaluation index is the number of data points in the comprehensive evaluation index curve of horizontal well depth and perforation location.

2. The method for selecting the perforation location of a horizontal well in a coal seam roof according to claim 1, characterized in that, In the coal seam distance determination step, logging-while-drilling data and cementing quality logging data of the horizontal section of the horizontal well in the coal seam roof are collected, as well as logging data of boreholes around the horizontal well in the coal seam roof and coal seam depth data. The natural gamma ray data of the horizontal well in the coal seam roof is compared with the natural gamma ray curves of the target coal seam and the top and bottom plates of the coalbed gas wells near the horizontal well. The relative distance between the wellbore trajectory of the horizontal well in the roof and the target coal seam is further determined by combining the contour map of the bottom plate of the target coal seam and the drilling cuttings identification data, and then normalized.

3. The method for selecting the location of perforations in a horizontal well in a coal seam roof according to claim 1, characterized in that, In the step of calculating the clay content, the upward gamma value is taken for the well trajectory at the top of the coal seam, the average gamma value is taken for the well trajectory in the coal seam, and the downward gamma value is taken for the well trajectory at the bottom of the coal seam. Furthermore, the clay content is calculated based on the following formula: SH=(GR-GR min ) / (GR max -GR min ) (1) V sh ＝(2 GCUR·SH -1) / (2 GCUR -1) (2) In the formula: GR is the response value of the natural gamma curve; GR min The natural gamma logging response value for pure sandstone near the target coal seam; GR max SH represents the natural gamma logging response value in pure mudstone near the target coal seam; SH is the relative value of the natural gamma curve; V sh The value represents the mud content of the formation; GCUR is an empirical coefficient.

4. The method for selecting the location of perforations in a horizontal well in the roof of a coal seam according to claim 1, characterized in that, In the evaluation index determination step, the interpretation results of the cementing quality of the horizontal section are assigned values ​​based on the cementing quality test results of the horizontal well in the coal seam roof. By examining the magnetic positioning data in the well logging interpretation data of the horizontal well in the coal seam roof, and based on the production casing coupling data of the horizontal section of the horizontal well in the coal seam roof, values ​​are assigned to the safety level of the distance from the production casing coupling during fracturing and stimulation at each point in the horizontal section.

Images