CN-122014190-A - Hydraulic sand fracturing combined depressurization design method for carbonate rock

CN122014190ACN 122014190 ACN122014190 ACN 122014190ACN-122014190-A

Abstract

The invention discloses a hydraulic sand-adding fracturing combination depressurization design method for carbonate rock, which comprises the steps of firstly pretreating by adopting low-displacement injection conventional acid, secondly injecting high-viscosity fracturing fluid, starting and extending artificial cracks, thirdly injecting gelled acid, reducing the construction pressure at the far end of the cracks by utilizing the characteristics of low reaction rate of the gelled acid and a carbonate rock reservoir, fourthly injecting high-viscosity fracturing fluid and carrying small-particle-size propping agent slugs, reducing fracturing fluid loss, and simultaneously promoting main seam extension, fifth, injecting high-viscosity fracturing fluid carrying large-particle-size propping agent, improving the diversion capacity of the artificial cracks, sixth, injecting high-viscosity fracturing fluid to replace sand-carrying fluid in the well, avoiding sand setting in the well, and further reducing the construction pressure at the far end of the cracks by adopting the combined depressurization design method, so that the smooth sand adding of the carbonate rock reservoir is ensured.

Inventors

JIANG YANFANG
ZHU XINCHUN
LI LINGCHUAN
LI XIAOMING
LI YANGYANG
ZHANG LIWEN

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 (10)

1. A hydraulic sand fracturing combined depressurization design method for carbonate rock is characterized by comprising the following steps of Step one, injecting conventional acid with low discharge capacity for pretreatment, and reducing construction pressure near a near-wellbore; injecting high-viscosity fracturing fluid, and starting and extending artificial cracks; Injecting gelled acid, and reducing the construction pressure of the far end of the crack by utilizing the characteristics of low reaction rate and the like of the gelled acid and the carbonate reservoir; Injecting high-viscosity fracturing fluid and carrying small-particle-size propping agent slugs, reducing the fluid loss of the fracturing fluid and simultaneously promoting the extension of main joints; Injecting high-viscosity fracturing fluid to carry a large-particle-size propping agent, and improving the diversion capacity of the artificial fracture; and step six, injecting high-viscosity fracturing fluid to replace sand-carrying fluid in the shaft, so as to avoid sand setting of the shaft.
2. The hydraulic sand fracturing combination depressurization design method for carbonate rock is characterized in that conventional acid in the first step is hydrochloric acid, the mass fraction of the conventional acid is 20%, and the injection displacement of the conventional acid is 1.5-2 square/min.
3. The method for designing the hydraulic sand fracturing combination depressurization of the carbonate rock according to claim 2, wherein a slow auxiliary agent is further added in the first step, and the auxiliary agent comprises an etching agent, an iron ion stabilizer and an acid fracturing cleanup additive.
4. The hydraulic sand fracturing combination depressurization design method for carbonate rock, which is disclosed in claim 1, is characterized in that the amount of the fracturing fluid in the second step is required to be referred to the effective distance, the seam length and the displacement of the action of gelled acid.
5. The method for designing the hydraulic sand fracturing combination depressurization of carbonate rock according to claim 4, wherein the dosage of the fracturing fluid is calculated by following a volume balance equation by adopting the following formula Wherein Q (t) is injection amount, t is construction time, delta, A is crack area, w is crack width, C is fluid loss coefficient, error compensation function of erfc (x) is obtained by checking function table.
6. The hydraulic sand fracturing combination depressurization design method for carbonate rock according to claim 5, characterized in that the action distance of gelled acid in the third step is calculated by adopting the following convective diffusion partial differential equation according to the experimental test result of the reaction rate of acid rock Wherein, C is C (x, y), acid concentration at any position in the crack, u x is acid liquor velocity component in x direction, u y is acid liquor velocity component in y direction, and D H+ is effective mass transfer coefficient.
7. The method for designing the hydraulic sand fracturing combination depressurization of the carbonate rock according to claim 6, wherein a boundary condition is given according to an actual flow reaction condition by using a convective diffusion partial differential equation, and the boundary condition of the reaction of the hydrochloric acid and the rock is as follows:
8. the carbonate hydraulic sand fracturing combination depressurization design method is characterized in that under the boundary condition of the formula (4), the partial differential equation (1) is drawn into a layout form by using the analytical solution given by the heat conduction field under the same boundary condition.
9. The method for designing the hydraulic sand fracturing combination depressurization of carbonate rock according to claim 8, wherein in a layout form, the ordinate is the Pickering number without the influence of the hydraulic sand fracturing combination depressurization The abscissa is free of the distance Each curve corresponds to a different no-therefore acid concentration C D ＝C/C 0 .
10. The hydraulic sand fracturing combination depressurization design method for the carbonate rock is characterized in that in the fourth step, 70/140-mesh ceramsite is adopted as the medium-and-large-particle-size propping agent, 40/70-mesh ceramsite is adopted as the medium-and-large-particle-size propping agent, 30/50-mesh propping agent is adopted at a seam, the seam flow conductivity is improved, the displacing liquid in the sixth step is 10 square Gao Nianye, and the remaining flowback liquid is used, so that the cost is reduced.

Description

Hydraulic sand fracturing combined depressurization design method for carbonate rock Technical Field The invention relates to the technical field of low-permeability compact carbonate reservoir reconstruction, in particular to a hydraulic sand fracturing combined depressurization design method for carbonate. Background At present, aiming at carbonate reservoirs, acid fracturing technology is mainly adopted at home and abroad to communicate with a fracture hole, and meanwhile, a high-conductivity artificial fracture channel is formed through non-uniform etching, so that the yield of a single well is improved. Aiming at a hypotonic compact carbonate reservoir, the fracture and cavity development heterogeneity degree is high, and in order to further improve the transformation volume and the probability of communicating the fracture and cavity, the hydraulic sand fracturing technology is adopted in the current test. However, the Young modulus and the extension pressure gradient of the carbonate reservoir are higher than those of the sandstone reservoir, the seam width is narrow, the sand adding is difficult, and the crack extension difficulty is high, so that how to reduce the construction pressure and smoothly sand adding are key to guaranteeing the fracturing construction effect of the compact carbonate reservoir. At present, the prior art discloses various methods for reducing construction pressure, such as a method for reducing the fracturing fracture pressure and the extending pressure of dry thermal rock disclosed in a Chinese patent with the publication number of CN113062732A and application thereof, cold fluid is injected into the mixture through variable displacement pulse to reduce the fracturing fracture pressure and the extending pressure of the dry thermal rock, the method can reduce the fracturing pressure by more than 20 percent and reduce the extending fracture pressure of the fracture by more than 10 percent, a prepositive acid liquid and an acid pretreatment method for deep shale gas horizontal well fracturing disclosed in a Chinese patent with the publication number of CN107446566A, the construction pressure near perforation blastholes is reduced by 10-20 percent of earth acid, the crack expansion form is controlled and the staged fracturing effect is improved, and a Chinese patent with the publication number of CN107842353A discloses a method for optimizing shale reservoir fracturing pretreatment acid liquid, and a corrosion rate test, an acidification permeability improvement test and a tensile strength reduction test are carried out, preferably a system with the highest fracturing pressure reduction capability is carried out on a specific shale reservoir, and further requirements on construction equipment power and bearing capacity are reduced. In summary, the prior art mainly reduces the construction pressure in the fracturing construction process of dry-hot rock and shale reservoirs, and no research on reducing the hydraulic sand fracturing construction pressure of carbonate reservoirs is seen. Disclosure of Invention The invention aims to provide a hydraulic sand fracturing combination depressurization design method for carbonate reservoirs, and aims to solve the problem that the hydraulic sand fracturing pressure and the remote extension pressure of artificial cracks of a carbonate reservoir are not effectively reduced, and smooth sand adding is guaranteed. The invention is realized by a hydraulic sand fracturing combination depressurization design method of carbonate rock, which comprises the following steps of The method comprises the steps of firstly, pretreating by injecting conventional acid with low discharge capacity, and reducing construction pressure near a near-well shaft; injecting high-viscosity fracturing fluid, and starting and extending artificial cracks; Injecting gelled acid, and reducing the construction pressure of the far end of the crack by utilizing the characteristics of low reaction rate and the like of the gelled acid and the carbonate reservoir; Injecting high-viscosity fracturing fluid and carrying small-particle-size propping agent slugs, reducing the fluid loss of the fracturing fluid and simultaneously promoting the extension of main joints; Injecting high-viscosity fracturing fluid to carry a large-particle-size propping agent, and improving the diversion capacity of the artificial fracture; and step six, injecting high-viscosity fracturing fluid to replace sand-carrying fluid in the shaft, so as to avoid sand setting of the shaft. Preferably, the conventional acid in the first step is hydrochloric acid, the mass fraction of which is 20%, and the injection displacement of the conventional acid is 1.5-2 square/min. Preferably, a slow aid is further added in the first step, wherein the slow aid comprises an etching agent, an iron ion stabilizer and an acid pressure discharge aid. Preferably, the dosage of the fracturing fluid in the second step is referred