Method for characterizing balanced expansion degree of fractures of segmented multi-cluster fracturing of horizontal well

Abstract

The invention discloses a characterization method for the balanced expansion degree of horizontal well segmented multi-cluster fracturing fractures, and the characterization method is specifically implemented according to the following steps: step 1, obtaining reservoir geological parameters, obtaining fracturing design parameters or obtaining the liquid inlet amount and the sand inlet amount according to working conditions, the maximum value MAX of the single-cluster fracture length in fracturing of each section, the minimum value MIN of the single-cluster fracture length and the average value AVERAGE of the fracture length of each cluster are obtained; 2, the non-uniformity index Mi of fracturing of each section is calculated; and 3, according to the non-uniformity index Mi of the single-section fracturing obtained in the step 2, obtaining the segmented multi-cluster fracturing crack propagation equilibrium degree M'of the whole horizontal well. According to the characterization method, the equilibrium expansion degree of the multi-cluster fracturing cracks can be quantitatively evaluated, and the accuracy is high.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field exploration and development, and in particular relates to a method for characterizing the balanced expansion degree of staged multi-cluster fracturing cracks in a horizontal well. Background Art

[0002] Horizontal well segmented multi-cluster fracturing is the main technical means for the transformation of low permeability, tight oil, shale oil and other difficult-to-use reservoirs, and the balanced expansion degree of multi-cluster fractures is crucial to the evaluation of the transformation effect. At present, there are two main means to evaluate the balanced expansion degree of multi-cluster fractures. One is to use professional fracturing simulation software to simulate segmented multi-cluster fracturing, which can obtain the fracture length of each cluster and show the fracture extension through the fracture length of each cluster, but there is no quantitative indicator to evaluate its overall balanced expansion degree, and its evaluation accuracy is poor; the other is to use distributed optical fiber monitoring during the fracturing process to quantitatively interpret the liquid and sand inflow of each cluster under the condition of single-stage multi-cluster combined pressure in real time, and show the fracture extension of each cluster through the value of the liquid and sand inflow of each cluster. The limitation of this method is that even if the liquid and sand inflow of each cluster are obtained, there is still no quantitative indicator to evaluate its overall balanced expansion degree; in addition, affected by the heterogeneity of the reservoir, the amount of liquid and sand inflow of each cluster cannot accurately reflect the size of the fracture length of each cluster, so this method is not reliable and its evaluation accuracy is poor. Summary of the invention

[0003] The purpose of the present invention is to provide a method for characterizing the balanced expansion degree of multi-cluster hydraulic fracturing cracks in horizontal wells, which can quantitatively evaluate the balanced expansion degree of multi-cluster hydraulic fracturing cracks with high accuracy.

[0004] The technical solution adopted by the present invention is a method for characterizing the balanced expansion degree of multi-cluster fracturing cracks in horizontal wells, which is specifically implemented according to the following steps:

[0005] Step 1, obtaining reservoir geological parameters, obtaining fracturing design parameters or obtaining fluid injection volume and sand injection volume according to working conditions, and then obtaining the maximum value MAX of a single cluster fracture length in each stage of fracturing, the minimum value MIN of a single cluster fracture length, and the average value AVERAGE of each cluster fracture length;

[0006] Step 2, respectively calculating the heterogeneity index Mi of each stage of fracturing;

[0007] Step 3: According to the single-stage fracturing heterogeneity index Mi obtained in step 2, the overall segmented multi-cluster fracturing crack expansion equilibrium degree M' of the horizontal well is obtained.

[0008] The present invention is also characterized in that:

[0009] In step 1, the working conditions include a horizontal well without fiber optic testing during the fracturing process and a horizontal well with fiber optic testing during the fracturing process.

[0010] When a horizontal well is not equipped with fiber optic testing during the fracturing process, the reservoir geological parameters and fracturing design parameters of the fracturing well are input through professional fracturing simulation software, and then a segmented multi-cluster fracturing simulation is performed to obtain the fracture lengths of all clusters in each segment of the fracturing, thereby obtaining the maximum value MAX of the single cluster fracture length in each segment of the fracturing, the minimum value MIN of the single cluster fracture length, and the average value AVERAGE of the fracture lengths of each cluster.

[0011] When a horizontal well is equipped with fiber optic testing during the fracturing process, the reservoir geological parameters of the fracturing well and the liquid and sand inflow of each cluster of fractures in each fracturing section obtained by fiber optic monitoring interpretation are input into the fracturing software based on the fiber optic monitoring interpretation results, and then the fracture lengths of all clusters in each fracturing section are simulated, and then the maximum value MAX of the single cluster fracture length in each fracturing section, the minimum value MIN of the single cluster fracture length, and the average value AVERAGE of the fracture lengths of each cluster are obtained.

[0012] In step 2, the expression of the heterogeneity index Mi of each stage of fracturing is:

[0013] Mi=(MAX-MIN) / AVERAGE,i=1,2,……,n

[0014] Where MAX is the maximum value of the single cluster fracture length in this section of fracturing; MIN is the minimum value of the single cluster fracture length in this section of fracturing; AVERAGE is the average value of the fracture lengths of each cluster in this section of fracturing; i represents the number of fracturing stages.

[0015] In step 3, the expression of the balanced degree M' of the fracture extension of the segmented multi-cluster fracturing of the horizontal well as a whole is:

[0016] M'=(M1+M2+……+Mn) / n

[0017] Where n is the total number of stages of horizontal well fracturing stimulation.

[0018] In step 3, when M'≤0.8, it indicates that the fracture expansion after horizontal well fracturing is relatively balanced and the reservoir reconstruction is relatively sufficient; when 0.8<M'≤1.2, it indicates that the fracture expansion balance after horizontal well fracturing is at a medium level; when M'>1.2, it indicates that the fracture expansion balance after horizontal well fracturing is poor and the reservoir reconstruction is insufficient.

[0019] The beneficial effects of the present invention are as follows: the characterization method of the balanced expansion degree of the horizontal well segmented multi-cluster fracturing cracks of the present invention can objectively and quantitatively reflect the balanced expansion degree of the horizontal well segmented multi-cluster fracturing cracks, and its characterization result has high accuracy and strong reliability, which adds a new evaluation method to the evaluation of the effect of the horizontal well segmented multi-cluster fracturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1It is a flow chart of the method for characterizing the balanced expansion degree of multi-cluster hydraulic fracturing cracks in horizontal wells of the present invention;

[0021] Figure 2 This is a simulation diagram of the expansion of multiple clusters of fractures in the second stage of the multi-cluster fracturing of a horizontal well in Example 4 of the present invention. DETAILED DESCRIPTION

[0022] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Example 1

[0024] The characterization method of the balanced expansion degree of the multi-cluster hydraulic fracturing in the horizontal well of the present invention is as follows: Figure 1 As shown, the specific implementation steps are as follows:

[0025] Step 1, obtaining reservoir geological parameters, obtaining fracturing design parameters or obtaining fluid injection volume and sand injection volume according to working conditions, and then obtaining the maximum value MAX of a single cluster fracture length in each stage of fracturing, the minimum value MIN of a single cluster fracture length, and the average value AVERAGE of each cluster fracture length;

[0026] The working conditions include horizontal wells that were not equipped with fiber optic testing during the fracturing process and horizontal wells that were equipped with fiber optic testing during the fracturing process;

[0027] When a horizontal well is not equipped with fiber optic testing during the fracturing process, the reservoir geological parameters and fracturing design parameters of the fracturing well are input through professional fracturing simulation software (such as Kinetix shale fracturing simulation software), and then a segmented multi-cluster fracturing simulation is performed to obtain the fracture lengths of all clusters in each segment of the fracturing, thereby obtaining the maximum value MAX of the single cluster fracture length in each segment of the fracturing, the minimum value MIN of the single cluster fracture length, and the average value AVERAGE of the fracture lengths of each cluster.

[0028] When a horizontal well is equipped with fiber optic testing during the fracturing process, the reservoir geological parameters of the fracturing well and the liquid and sand inflow of each cluster of fractures in each fracturing stage obtained by fiber optic monitoring interpretation are input into the fracturing software (such as Kinetix shale fracturing simulation software) based on the fiber optic monitoring interpretation results, and the fracture lengths of all clusters in each fracturing stage are simulated to obtain the maximum value MAX of the single cluster fracture length in each fracturing stage, the minimum value MIN of the single cluster fracture length, and the average value AVERAGE of the fracture lengths of each cluster.

[0029] Step 2, respectively calculating the heterogeneity index Mi of each stage of fracturing;

[0030] The expression of the heterogeneity index Mi of each stage of fracturing is:

[0031] Mi=(MAX-MIN) / AVERAGE,i=1,2,……,n

[0032] In the formula, MAX is the maximum value of the single cluster fracture length in this section of fracturing; MIN is the minimum value of the single cluster fracture length in this section of fracturing; AVERAGE is the average value of the fracture lengths of each cluster in this section of fracturing; i represents the number of fracturing sections;

[0033] Step 3, obtaining the overall segmented multi-cluster fracturing crack expansion equilibrium degree M' of the horizontal well according to the single-stage fracturing heterogeneity index Mi obtained in step 2;

[0034] The expression of the balanced degree of fracture expansion M' of the overall segmented multi-cluster fracturing in the horizontal well is:

[0035] M'=(M1+M2+……+Mn) / n

[0036] Where n is the total number of stages of horizontal well fracturing transformation;

[0037] When M'≤0.8, it indicates that the fracture expansion after horizontal well fracturing is relatively balanced and the reservoir reconstruction is relatively sufficient; when 0.8<M'≤1.2, it indicates that the degree of fracture expansion balance after horizontal well fracturing is medium; when M'>1.2, it indicates that the degree of fracture expansion balance after horizontal well fracturing is poor and the reservoir reconstruction is insufficient.

[0038] Example 2

[0039] The method for characterizing the balanced expansion degree of multi-cluster hydraulic fracturing in a horizontal well of the present invention is specifically implemented according to the following steps:

[0040] Step 1: A shale oil reservoir is developed by horizontal wells, and the reservoir geological parameters are: reservoir permeability 0.1 millidarcy, porosity 8.5%, Young's modulus 24000 MPa, Poisson's ratio 0.21, horizontal maximum principal stress 33 MPa, horizontal minimum principal stress 28 MPa, vertical stress 42 MPa;

[0041] The horizontal well was not equipped with optical fiber testing during the fracturing process, so the fracturing design parameters of the well are: the average horizontal section length of the horizontal well used to develop the oil reservoir is 1,200 meters, the oil layer drilling rate is 88.3%, and the design adopts a segmented multi-cluster fracturing transformation mode, with an average of 10 segments per well, 10 clusters of perforations in a single segment, 10 clusters of combined fracturing in each segment, sand addition intensity of 3.5 tons / meter, liquid injection intensity of 20 cubic meters / meter, and injection displacement of 14 cubic meters / minute; the reservoir geological parameters and fracturing design parameters of the fracturing well are input through professional fracturing simulation software, and then the segmented multi-cluster fracturing simulation is performed to obtain the fracture length of all clusters in each segment of the fracturing, and then the maximum value MAX of the single cluster fracture length in each segment of the fracturing, the minimum value MIN of the single cluster fracture length, and the average value AVERAGE of the fracture length of each cluster are obtained, such as Figure 2As shown, taking the second section as an example, there are 10 clusters in total in this section, among which the maximum value MAX of the single cluster seam length is 270 meters, the minimum value MIN of the single cluster seam length is 126 meters, and the average value AVERAGE of the seam length of each cluster is 185 meters.

[0042] Step 2, calculate the heterogeneity index M2 of the second stage fracturing = (270-126) / 185 = 0.78. The heterogeneity indexes of the 10 stages of fracturing in the horizontal well calculated by this formula are 0.93, 0.78, 1.12, 1.05, 1.25, 1.38, 1.24, 0.66, 1.48, and 0.75, respectively.

[0043] Step 3, the overall balanced degree of fracture expansion of the segmented multi-cluster fracturing of the horizontal well is M'=(M1+M2+...M10) / 10, then M'=(0.93+0.78+1.12+1.05+1.25+1.38+1.24+0.66+1.48+0.75) / 10=1.06. It can be seen that in the interval of 0.8<M'≤1.2, it indicates that the balanced degree of fracture expansion after fracturing of the horizontal well is at a medium level, and the degree of reservoir transformation is general.

[0044] Example 3

[0045] The method for characterizing the balanced expansion degree of multi-cluster hydraulic fracturing in a horizontal well of the present invention is specifically implemented according to the following steps:

[0046] Step 1: A shale gas reservoir is developed by horizontal wells, and the reservoir geological parameters are: reservoir permeability 0.15 millidarcy, porosity 9.2%, Young's modulus 22000MPa, Poisson's ratio 0.22, horizontal maximum principal stress 35MPa, horizontal minimum principal stress 31MPa, vertical stress 43MPa;

[0047] The horizontal well was not equipped with optical fiber testing during the fracturing process, so the fracturing design parameters of the well were as follows: the average horizontal section length of a single well for the development of the reservoir was 600 meters, the oil layer drilling rate was 78.5%, and the design adopted a segmented multi-cluster fracturing transformation mode, with an average of 6 segments of single well fracturing, 5 clusters of perforation in a single segment, 5 clusters of combined fracturing in each segment, sand addition intensity of 3.2 tons / meter, liquid injection intensity of 25 cubic meters / meter, and injection displacement of 10 cubic meters / minute; the reservoir geological parameters and fracturing design parameters of the fracturing well were input through professional fracturing simulation software, and then the segmented multi-cluster fracturing simulation was performed to obtain the fracture lengths of all clusters in each segment of the fracturing, and then the maximum value MAX of the single cluster fracture length in each segment of the fracturing, the minimum value MIN of the single cluster fracture length, and the average value AVERAGE of the fracture length of each cluster were obtained, as shown in Table 1.

[0048] Step 2, use the formula Mi = (MAX-MIN) / AVERAGE, i = 1, 2, ..., 6 to calculate the non-uniformity index Mi of each segment.

[0049] Table 1 Detailed calculation table of heterogeneity index of each section of a shale gas horizontal well

[0050]

[0051] Step 3: The overall balanced degree of fracture expansion of the horizontal well segmented multi-cluster hydraulic fracturing is M' = (M1 + M2 + ... M6) / 6.

[0052] M'=(0.37+0.67+0.46+0.19+0.61+0.38) / 6=0.45

[0053] It can be seen that M'<0.8, which indicates that the fracture expansion after horizontal well fracturing is more balanced and the reservoir transformation is more sufficient.

[0054] Example 4

[0055] The method for characterizing the balanced expansion degree of multi-cluster hydraulic fracturing in a horizontal well of the present invention is specifically implemented according to the following steps:

[0056] Step 1: A certain ultra-low permeability reservoir is developed by horizontal wells, and the reservoir geological parameters are: reservoir permeability 0.35 millidarcy, porosity 11.2%, Young's modulus 21500MPa, Poisson's ratio 0.23, horizontal maximum principal stress 31MPa, horizontal minimum principal stress 27MPa, vertical stress 35MPa;

[0057] The horizontal wells in this reservoir have an average horizontal section length of 500 meters and an oil layer drilling rate of 73.5%. The segmented multi-cluster fracturing transformation mode is adopted, with an average of 4 sections per well, 3 clusters of perforation in a single section, and 3 clusters per section. The horizontal well is equipped with fiber optic testing during the fracturing process, and the amount of liquid and sand in each cluster of fractures in each section of the fracturing is obtained through fiber optic monitoring interpretation. The reservoir geological parameters of the fracturing well and the amount of liquid and sand in each cluster of fractures in each section of the fracturing obtained by fiber optic monitoring interpretation are input into the Kinetix fracturing software, and then the length of all clusters in each section of the fracturing is simulated, and then the maximum value MAX of the single cluster fracture length in each section of the fracturing, the minimum value MIN of the single cluster fracture length, and the average value AVERAGE of the fracture length of each cluster are obtained, as shown in Table 2.

[0058] Step 2, use the formula Mi = (MAX-MIN) / AVERAGE, i = 1, 2, 3, 4 to calculate the non-uniformity index Mi of each segment.

[0059] Table 2 Detailed calculation table of heterogeneity index of each section of horizontal well in an ultra-low permeability reservoir

[0060]

[0061]

[0062] Step 3, the overall staged multi-cluster fracturing fracture expansion balance degree of the horizontal well is M'=(M1+M2+...M4) / 4, then M'=(1.42+1.33+1.26+0.98) / 4=1.25;

[0063] It can be seen that M'>1.2, indicating that the fracture expansion balance after horizontal well fracturing is poor and the reservoir reconstruction is insufficient.

Claims

1. A method for characterizing the balanced expansion degree of multi-cluster fracturing in horizontal wells, characterized in that: Follow the steps below to implement it: Step 1, obtaining reservoir geological parameters, obtaining fracturing design parameters or obtaining fluid injection volume and sand injection volume according to working conditions, and then obtaining the maximum value MAX of a single cluster fracture length, the minimum value MIN of a single cluster fracture length, and the average value AVERAGE of each cluster fracture length in each stage of fracturing; Step 2, respectively calculating the heterogeneity index Mi of each stage of fracturing; Step 3: According to the single-stage fracturing heterogeneity index Mi obtained in step 2, the overall segmented multi-cluster fracturing crack expansion equilibrium degree M' of the horizontal well is obtained.

2. The method for characterizing the balanced expansion degree of multi-cluster hydraulic fracturing in horizontal wells according to claim 1, characterized in that: In step 1, the working conditions include a horizontal well without fiber optic testing during the fracturing process and a horizontal well with fiber optic testing during the fracturing process.

3. The method for characterizing the balanced expansion degree of multi-cluster hydraulic fracturing in horizontal wells according to claim 2, characterized in that: When a horizontal well is not equipped with fiber optic testing during the fracturing process, the reservoir geological parameters and fracturing design parameters of the fracturing well are input through professional fracturing simulation software, and then a segmented multi-cluster fracturing simulation is performed to obtain the fracture lengths of all clusters in each segment of the fracturing, thereby obtaining the maximum value MAX of the single cluster fracture length in each segment of the fracturing, the minimum value MIN of the single cluster fracture length, and the average value AVERAGE of the fracture lengths of each cluster.

4. The method for characterizing the balanced expansion degree of multi-cluster fracturing in horizontal wells according to claim 2, characterized in that: When a horizontal well is equipped with fiber optic testing during the fracturing process, the reservoir geological parameters of the fracturing well and the liquid and sand inflow of each cluster of fractures in each fracturing section obtained by fiber optic monitoring interpretation are input into the fracturing software based on the fiber optic monitoring interpretation results, and then the fracture lengths of all clusters in each fracturing section are simulated, and then the maximum value MAX of the single cluster fracture length in each fracturing section, the minimum value MIN of the single cluster fracture length, and the average value AVERAGE of the fracture lengths of each cluster are obtained.

5. The method for characterizing the balanced expansion degree of multi-cluster fracturing in horizontal wells according to claim 1, characterized in that: In step 2, the expression of the heterogeneity index Mi of each stage of fracturing is: Mi=(MAX-MIN) / AVERAGE,i=1,2,……,n Where MAX is the maximum value of the single cluster fracture length in this section of fracturing; MIN is the minimum value of the single cluster fracture length in this section of fracturing; AVERAGE is the average value of the fracture lengths of each cluster in this section of fracturing; i represents the number of fracturing stages.

6. The method for characterizing the balanced expansion degree of multi-cluster hydraulic fracturing in horizontal wells according to claim 5, characterized in that: In step 3, the expression of the balanced degree M' of the fracture extension of the segmented multi-cluster fracturing of the horizontal well as a whole is: M'=(M1+M2+……+Mn) / n Where n is the total number of stages of horizontal well fracturing stimulation.

7. The method for characterizing the balanced expansion degree of multi-cluster fracturing in horizontal wells according to claim 1, characterized in that: In step 3, when M'≤0.8, it indicates that the fracture expansion after horizontal well fracturing is relatively balanced and the reservoir reconstruction is relatively sufficient; when 0.8<M'≤1.2, it indicates that the fracture expansion balance after horizontal well fracturing is at a medium level; when M'>1.2, it indicates that the fracture expansion balance after horizontal well fracturing is poor and the reservoir reconstruction is insufficient.

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