LARGE-VOLUME ACID TREATMENT METHOD FOR CARBONATE BED Russian patent published in 2014 - IPC E21B43/27 

FIELD: oil and gas industry.

SUBSTANCE: large-volume acid treatment method for carbonate bed includes surveys and identification of the bed areas with different permeability, running-in of filters with different density of perforation at the tubing string to a horizontal well, injection of acid into open horizontal wellbore, acid displacement, washing of the well and its starting-up. At that each section with permeability differing per more than 20% of the neighbouring section, and isolated by the packers installed at filters. Density of the filter perforation at each section is identified on the basis of the following ratio: , where C₁, C₂, C_n are coefficients of the well hydrodynamic efficiency as per origin of opening along horizontal bore of the well; R₁, R₂, R_n is designed depth of acid penetration to the rock, m; k₂, k_n is permeability of the bed section, m²; h_n is thickness of the section bed, m; r_c is filter radius, m. Alkali is injected to tubular annulus up to the productive stratum roof to neutralise acid or a packer is set at the productive stratum roof, at that tubular annulus is filled with process water. Alkali or water volume V is defined as per the formula V=π·H·(R²-r²), m³, where H is well depth up to the productive stratum roof, m; R² is internal radius of the production casing, m; r² is outer radius of the tubing string, m; hydrochloric acid is injected to the tubing string with concentration of 10-20% at wellhead pressure P_w=(0.009-0.01)·H, MPa, in volume V_c equal to V_c=(0.007-0.008)·L·h, m³, where L is length of the horizontal wellbore, m; h is thickness of the bed, m; acid displacement is made by oil in the volume equal to volume of inner space of the tubing string with filters.

EFFECT: higher yield owing increased higher coverage.

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