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CN-122014189-A - Deep coal seam gas fracturing design method

CN122014189ACN 122014189 ACN122014189 ACN 122014189ACN-122014189-A

Abstract

The invention discloses a deep coal seam gas fracturing design method which comprises the following steps of S100, adopting a low-displacement pump to fill earth acid to reduce fracturing pressure, wherein the displacement of the pumped earth acid is 1-2m 3 /min, S200, adopting a low-concentration surfactant fracturing fluid in a low-to-high variable displacement mode in a pre-fluid stage, adopting a low-to-high variable displacement mode in the pre-fluid stage, and adopting a displacement of 2-4-6-8-10m 3 /min, wherein the viscosity of the low-concentration surfactant fracturing fluid is 5-10 mPa.s under the ground condition, adopting 170S ‑1 to continuously shear for 2 hours under the formation temperature condition, the apparent viscosity is kept above 5 mPa.s, S300, adopting a continuous sand adding mode in a sand carrying stage, carrying a super-low density propping agent in a step sand ratio mode, filling a main crack, and then carrying a concretionable tectorial membrane propping agent in a high sand ratio mode, filling a seam mouth, S400, adopting active water displacement to ensure clean coal well, and improving the coal seam production and coal seam production.

Inventors

  • LIANG WENLONG
  • ZHU XINCHUN
  • HU AIGUO
  • CHANG HUI
  • LU JIAOPING
  • WANG ZIYU

Assignees

  • 中国石油化工股份有限公司
  • 中国石油化工股份有限公司华北油气分公司

Dates

Publication Date
20260512
Application Date
20241111

Claims (7)

  1. 1. A deep coal seam gas fracturing design method is characterized by comprising the following steps: S100, adopting a low-displacement pump to inject earth acid to reduce the cracking pressure; s200, pumping low-concentration surfactant fracturing fluid from a low-to-high displacement mode in a pre-fluid stage, adopting a pulse sand adding mode, and adding an ultralow-density proppant slug; S300, injecting medium-concentration surfactant fracturing fluid by a large displacement pump in a sand-carrying fluid stage, adopting a continuous sand adding mode, carrying an ultra-low density propping agent by a stepped sand ratio, filling a main crack, carrying a concretionary tectorial membrane propping agent by a high sand ratio, and filling a crack; S400, adopting active water to displace in a large displacement mode, and ensuring the cleanness of a shaft.
  2. 2. The method for designing deep coal seam gas fracturing according to claim 1, wherein in the step S100, the displacement of the pumping earth acid is 1-2m 3 /min.
  3. 3. The method for designing deep coal seam gas fracturing according to claim 1, wherein in the step S200, the displacement is 2-4-6-8-10m 3 /min in a low-to-high displacement mode in the pre-fluid stage.
  4. 4. The deep coal seam gas fracturing design method according to claim 1, wherein the viscosity of the low-concentration surfactant fracturing fluid is 5-10 mPa.s under the ground condition, 170s -1 are adopted for continuous shearing for 2 hours under the formation temperature condition, and the apparent viscosity is kept above 5 mPa.s.
  5. 5. The method for designing deep coal seam gas fracturing according to claim 1, wherein in the step S300, the medium concentration surfactant fracturing fluid has a viscosity of >40 mPa-S under ground conditions, is continuously sheared for 2 hours by 170S -1 under formation temperature conditions, the apparent viscosity is maintained above 20 mPa-S, and the residue content is <10mg/l.
  6. 6. The method according to claim 1, wherein in the step S300, the surface coating material of the curable coating proppant is softened and adhered under the formation temperature and pressure conditions.
  7. 7. The method according to claim 1, wherein in the step S400, the active water is 2% potassium chloride active water, and the displacement of the potassium chloride active water may be similar to a step displacement design.

Description

Deep coal seam gas fracturing design method Technical Field The invention relates to the technical field of coal bed gas exploration and development, in particular to a deep coal bed gas fracturing design method. Background Coal bed gas is a kind of natural gas which is self-generated and self-stored in coal-forming stratum and is non-conventional, and its main component is CH 4, accounting for above 90%. Coalbed methane is produced in the coal seam and stored in an adsorbed, free state in the coal seam and adjacent rock formations. The production of coalbed methane must establish effective communication channels between the coal bed and the wellbore, and the most effective way to create such communication channels is to hydraulically fracture the coal bed. Compared with conventional sandstone fracturing, the fracturing of the coal-bed gas well has the advantages that a coal-bed cutting system is developed, the fluid loss is serious, long seams are difficult to form, the coal bed is easy to adsorb and damage, the reservoir protection difficulty is high, and the pressed coal dust is easy to return out of a shaft along with the coal-bed gas. Coal beds generally exceeding 1500m are called deep layers, the technical difficulty of fracturing construction is far greater than that of conventional coal bed gas wells, and the development effect is generally not ideal. In the prior art, aiming at the fracturing of coal bed gas, there are various different patent technologies, such as patent publication number CN102562022A, CN108533241A, CN107288610A, CN106869889A and other patents. The technology mainly adopts large-displacement construction such as guanidine gum fracturing fluid, active water or slickwater, adopts a pulse or whole-course sand adding mode to carry propping agents with different particle diameters for carrying out fracturing design, and is not greatly different from conventional sandstone fracturing in the design method. In addition, the problem of coal dust spitting back after coal bed gas fracturing is not specifically designed. The patent with the publication number of CN112267867A mainly adopts an acidification sand adding mode, the whole process adopts acid liquor to reduce the construction pressure, the cost is high, a continuous sand adding mode is adopted in the sand adding process, the crack expansion is complex due to strong coal seam heterogeneity, the continuous sand adding difficulty is high, and meanwhile, the targeted design of the later pulverized coal and propping agent return is not carried out. Disclosure of Invention The invention aims to provide a deep coal seam gas fracturing design method which is used for solving the problems in the background technology, and the aims of reducing the fracture pressure of a stratum, improving the length of a supporting seam and avoiding returning pulverized coal after pressing are achieved through a pumping program and a propping agent design. The invention discloses a deep coal seam gas fracturing design method, which comprises the following steps: S100, adopting a low-displacement pump to inject earth acid to reduce the cracking pressure; s200, pumping low-concentration surfactant fracturing fluid from a low-to-high displacement mode in a pre-fluid stage, adopting a pulse sand adding mode, and adding an ultralow-density proppant slug; S300, injecting medium-concentration surfactant fracturing fluid by a large displacement pump in a sand-carrying fluid stage, adopting a continuous sand adding mode, carrying an ultra-low density propping agent by a stepped sand ratio, filling a main crack, carrying a concretionary tectorial membrane propping agent by a high sand ratio, and filling a crack; S400, adopting active water to displace in a large displacement mode, and ensuring the cleanness of a shaft. Further, in the step S100, the displacement of the pumping earth acid is 1-2m 3/min; Further, in the step S200, the displacement is 2-4-6-8-10m 3/min from low to high in the liquid-front stage; Further, the viscosity of the low-concentration surfactant fracturing fluid under the ground condition is 5-10 mPas, 170s -1 is adopted for continuous shearing for 2 hours under the formation temperature condition, and the apparent viscosity is kept above 5 mPas; further, in the step S300, the viscosity of the medium-concentration surfactant fracturing fluid under the ground condition is more than 40mpa·s, 170S -1 are adopted to continuously shear for 2 hours under the stratum temperature condition, the apparent viscosity is kept above 20mpa·s, the fracturing fluid has good gel breaking performance, the residue content is less than 10mg/l, and various indexes meet industry standards. Further, in the step S300, the surface coating material of the curable coated propping agent can be softened and adhered under the formation temperature and pressure conditions, and larger pores still exist between the curable coated propping agent after the curing. Further, in the s