CN-117473691-B - Shale gas horizontal well temporary plugging steering cracking pressure and cracking time calculation method

CN117473691BCN 117473691 BCN117473691 BCN 117473691BCN-117473691-B

Abstract

The invention provides a calculation method for temporary plugging turning cracking pressure and cracking time of a shale gas horizontal well. The method comprises the steps of obtaining engineering and geological parameters, calculating net pressure in an initial joint before temporary plugging according to the engineering and geological parameters, establishing an induced stress field calculation model around a clustered fracture by using a corrected two-dimensional displacement discontinuous method, solving the width of a hydraulic fracture and the induced stress field around the clustered fracture, and establishing a clustered fracture tensile fracture initiation pressure calculation model according to the clustered fracture induced stress and combining an original ground stress field, so that the natural fracture tensile fracture initiation pressure and the temporary plugging fracture initiation time can be solved when the rock gas horizontal well is subjected to temporary plugging diversion fracturing. According to the method, the influence of the fluid loss of the fracturing fluid on the cracking pressure is considered, the calculation result is more accurate, the temporary plugging and steering cracking pressure and the cracking time of the horizontal well can be calculated rapidly, and a theoretical basis can be provided for the optimal design of the temporary plugging and steering fracturing of the shale gas horizontal well.

Inventors

LIU JUN
ZHU JUHUI
CHEN MINGZHONG
LIU WEI
WANG DAN

Assignees

中国石油天然气集团有限公司
中国石油集团川庆钻探工程有限公司

Dates

Publication Date: 20260508
Application Date: 20220720

Claims (10)

1. The calculation method of the temporary plugging steering cracking pressure of the shale gas horizontal well is characterized by comprising the following steps of: S1, acquiring engineering and geological parameters, wherein the engineering and geological parameters comprise maximum horizontal main stress, minimum horizontal main stress, young modulus, poisson' S ratio, natural fracture tensile strength, natural fracture approach angle, fluid loss coefficient, hydraulic fracture length, hydraulic fracture height, fracturing fluid viscosity and pumping displacement; s2, calculating the net pressure in the initial joint before temporary plugging according to engineering and geological parameters; s3, establishing an induced stress field calculation model around the clustered cracks by using a modified two-dimensional displacement discontinuous method, and solving the width of the hydraulic cracks and the induced stress field around the clustered cracks, wherein the induced stress field calculation model around the clustered cracks comprises a crack unit stress balance equation, and the crack unit stress balance equation is as follows: wherein, (sigma n ) i is the normal stress of the i cell in the local coordinate system, pa; tangential strain of the j unit in a local coordinate system, m; The method comprises the steps of (1) setting a normal stress component of j units in a local coordinate system, wherein m is the normal stress component of j units caused by tangential displacement of the j units on an i unit, i is 1-N in value, i is the normal stress component of j units caused by discontinuous normal displacement of the j units on the i unit, i is 1-N in value, d ij is the distance between the i unit and the j unit of a crack, m is h f is the height of a hydraulic crack, m is a crack height correction coefficient, G ij is dimensionless, and i and j are any two discrete crack units; S4, according to the induced stress of the clustered cracks, combining an original ground stress field, establishing a clustered crack opening pressure calculation model, and calculating the natural crack opening pressure through a numerical calculation flow.
2. The method for calculating the temporary plugging and steering initiation pressure of the shale gas horizontal well according to claim 1, wherein in the step S3, the induced stress field calculation model around the clustered fracture further comprises an induced stress field solving equation, and the induced stress field solving equation is as follows: Wherein DeltaSigma xx is stratum induced stress component in x direction, deltaSigma yy is stratum induced stress component in y direction, pa, deltaSigma xy is stratum induced stress component in xy direction, pa, n j is the residual chord value of global coordinate z-axis and j unit local coordinate zeta-axis clamp angle, l j is the residual chord value of global coordinate x-axis and j unit local coordinate zeta-axis clamp angle, x and y represent global coordinates, zeta and zeta represent local coordinates corresponding to x and y coordinates respectively, F k is Papkovitch function bias equation, k epsilon { 3-6 }, G is shear modulus, pa.
3. The shale gas horizontal well temporary plugging turning initiation pressure calculation method according to claim 2, wherein the clustered fracture tenseness initiation pressure calculation model in step S4 comprises a fracture fluid net pressure calculation equation and a initiation pressure calculation equation, the fracture fluid net pressure calculation equation is as follows: Wherein p is the net pressure of fluid in the crack, pa, y is the coordinate value of the crack in the length direction, m, mu is the viscosity of the liquid, mPa.s, w f is the opening of the crack, m, q L is the fluid loss rate of the fracturing fluid, m/s, and t is the time, s; The fracture initiation pressure calculation equation is as follows: Wherein, the Sigma n is the normal stress of the natural fracture surface and MPa; The natural fracture unit positive stress at the intersection point of the natural fracture and the hydraulic fracture is MPa, and S t is the tensile strength of the natural fracture and MPa.
4. A method of calculating a shale gas horizontal well temporary plugging turning initiation pressure as claimed in claim 3, wherein step S4 comprises the sub-steps of: S41, determining the fluid loss rate of the fracturing fluid, and carrying out coupling solution on a net pressure calculation equation of the fluid in the fracture by combining the width of the hydraulic fracture determined in the step S3 to obtain the net pressure of the fluid in the fracture; S42, judging whether the net pressure of the fluid in the seam is converged, if so, calculating the volume of the pumped fluid, otherwise, returning the net pressure of the fluid in the seam obtained in the substep 41 to the step S3 for cyclic iterative calculation until the net pressure of the fluid in the seam is converged; S43, judging whether the seam flow is converged by setting a minimum error value of the seam flow, and when the difference between the pumping flow and the seam fluid flow and the fluid loss is smaller than the error value, namely the flow is converged, if not, changing the net pressure of the seam fluid and returning to the step S3 for cyclic iterative calculation until the seam flow is converged; S44, determining the normal stress of the natural fracture surface, substituting the normal stress into a fracture initiation pressure calculation equation by combining the natural fracture unit induced stress obtained in the step S3, and obtaining the natural fracture tensile fracture initiation pressure.
5. The method for calculating the temporary plugging-turning cracking pressure of the shale gas horizontal well according to claim 4, wherein the calculation equation of the net pressure in the initial joint is as follows: Wherein p 0 is the net pressure of fluid in the initial fracture, pa, h f is the height of the hydraulic fracture, m, mu is the viscosity of the fracturing fluid, mPa.s, L 0 is the length of the initial hydraulic fracture, m, v is the Poisson's ratio, dimensionless, E is Young's modulus, pa, q is the pumping displacement, and m 3 /s.
6. The method for calculating the temporary plugging and steering initiation pressure of the shale gas horizontal well according to claim 4, wherein in the substep S41, a joint fluid net pressure calculation equation is solved by adopting a backward implicit difference method, and a one-dimensional three-point difference format of the joint fluid net pressure calculation equation is as follows:
7. The method for calculating the temporary plugging turning initiation pressure of the shale gas horizontal well according to claim 4, wherein the intersection of the hydraulic fracture and the natural fracture is subjected to positive stress by a natural fracture unit: Wherein sigma H is the in-situ maximum horizontal main stress, MPa, sigma h is the in-situ minimum horizontal main stress, MPa, and theta is the included angle between the hydraulic fracture and the natural fracture.
8. The method for calculating the temporary plugging-turning initiation pressure of the shale gas horizontal well according to claim 4, wherein in the substep S43, the net pressure of the fluid in the seam is changed by increasing Δp, wherein Δp is a pressure increment.
9. The calculation method for the temporary plugging turning initiation time of the shale gas horizontal well is characterized by comprising the following steps of: determining the natural fracture tensile fracture initiation pressure by adopting the calculation method of the shale gas horizontal well temporary plugging steering fracture initiation pressure according to any one of claims 1-8; Judging whether the natural crack is cracked, if not, changing pumping time and recalculating the tensile cracking pressure of the natural crack, and if so, determining the current pumping time as the natural crack cracking time; the natural crack initiation judging expression is: wherein p is the fluid pressure at the intersection point of the hydraulic fracture and the natural fracture, and MPa; the natural fracture is the tensile fracture initiation pressure and MPa.
10. The method for calculating the temporary plugging-turning initiation time of the shale gas horizontal well according to claim 9, wherein the pumping time is changed by increasing Δt, wherein Δt is the pumping time increment.

Description

Shale gas horizontal well temporary plugging steering cracking pressure and cracking time calculation method Technical Field The invention relates to the technical field of unconventional oil and gas yield improvement, in particular to a calculation method of temporary plugging steering cracking pressure of a shale gas horizontal well and a calculation method of temporary plugging steering cracking time of the shale gas horizontal well. Background Shale gas is a huge reserve of unconventional natural gas resources, mainly reserved in shale reservoirs. Shale reservoirs usually have low-pore, low-permeability and other characteristics, so that the shale reservoirs are very unfavorable for oil and gas migration, and the shale gas exploitation difficulty is huge. Therefore, the shale gas natural yield is extremely low and has little commercial exploitation value without taking any effective stimulation measures. Compared with American sea shale, the shale reservoir in China has the characteristics of complex geological structure, strong heterogeneity, large ground stress difference and the like, and the fracture network difficulty is high. Due to the brittleness of shale, the stratum usually develops a large number of unactivated natural cracks, and temporary plugging steering is assisted to activate the natural cracks, so that the fracture network transformation is realized. The temporary plugging diversion fracturing is performed by adopting a temporary plugging agent to plug the crack by adopting a low-viscosity slick water pump in a horizontal well and matching with a temporary plugging diversion fracturing technology with high discharge capacity and low sand ratio, so that natural cracks can be effectively activated, and a high-diversion crack network system is formed. When the shale gas horizontal well is subjected to temporary plugging turning fracturing construction, the natural cracks are cracked under the action of fluid pressure in the cracks and hydraulic crack induced stress, so that a fracture network is formed. Therefore, the calculation of the crack initiation pressure and the determination of the temporary plugging turning initiation time are critical to the formation of a fracture network and the improvement of the yield increase effect of the temporary plugging turning fracture of the shale gas horizontal well. Therefore, calculation of the temporary plugging turning and cracking time of the shale gas horizontal well not only has theoretical references for forming a fracture network by temporary plugging turning and cracking of the shale gas horizontal well, but also has important guiding function for site construction. However, at present, theoretical research is still lacking in calculation of temporary plugging steering cracking pressure and cracking time of a shale gas horizontal well. For example, patent documents with publication number CN107609258a and published in 2018, 01 and 19 disclose a calculation method of a shale repeated fracturing turning crack initiation pressure, and a calculation method of shale repeated fracturing turning crack initiation pressure, which uses a two-dimensional displacement discontinuous method to obtain induced stress of a turning crack by dispersing shale gas repeated fracturing cracks, so as to calculate the initiation pressure, but the method does not consider the influence of the crack height on the induced stress. The invention name disclosed in 2018, 01 and 19 is a method for judging temporary plugging and cracking in a repeated fracturing well seam, and patent literature with publication number of CN106869892A describes a method for judging temporary plugging and cracking in a repeated fracturing well seam, and the method uses an analytic solution method to calculate induced stress at each point of a hydraulic fracture, but the method has low calculation precision. Because shale is relatively brittle, a large number of natural fractures are usually developed, the natural fractures are activated in the fracturing process, and the fracturing fluid flows into the activated natural fractures to cause a large amount of fluid loss. Therefore, the influence of the fracturing fluid loss is not negligible. Neither of the above methods takes into account the influence of the fluid loss of the fracturing fluid on the fracture initiation pressure, and the above methods cannot determine whether the diverted fracture initiates a fracture and the diverted fracture initiation time. Disclosure of Invention The present invention aims to address at least one of the above-mentioned deficiencies of the prior art. For example, the invention provides a calculation method for temporary plugging steering cracking pressure of a shale gas horizontal well, which aims to overcome the defect that the conventional calculation method for the cracking pressure does not consider the influence of fluid loss of fracturing fluid on the cracking pressure. In order to achieve the aim, t