RECOVERY METHOD FOR SOLID CARBONATE RESERVOIRS Russian patent published in 2017 - IPC E21B43/27 E21B43/18 E21B43/30 

FIELD: oil and gas industry.

SUBSTANCE: method includes drilling of horizontal wells, cementing of the annular space between the production casing and the reservoir in the horizontal shaft, the secondary penetration of the field with the orientation direction of perforation holes, conduction of multistage hydraulic fracturing, application of packers for separation of horizontal shaft to the sections, and product selection from the horizontal wells. According to the invention, the oil-saturated reservoir is selected with the average thickness H≥50 m and the average absolute permeability of less than 2 mD, the collector is drilled with parallel horizontal wells, the horizontal shafts of which are directed perpendicular to the main maximum collector voltage vector. Horizontal shafts are arranged vertically in three rows at the equal distances from one another h = (0.25-0.45) H. The horizontal shafts of the middle row are disposed in the plane between horizontal shafts of the upper and lower rows at the distance x = (1-5) h along the horizontal line. The length of each horizontal shaft is performed to be equal to 1 ≥ 8 h. In the wells of the upper row along the horizontal shaft the casing string and the cement stone lower half of the circumference is perforated, in the wells of the lower row - the upper, in the middle row wells the horizontal shafts are perforated along the whole area. All wells are subjected to the acid multistage hydraulic fracturing with the distance between the stages of not more than 50 m. Moreover, the location of each corresponding stage of the fracturing in the neighboring wells is performed in the staggered order. The rate and the volume of the pumped acid are determined according to the conditions, firstly, the formation of the carbonate dissolving structure, representing the branched hollows; secondly, the half-length of the fractures a = (0.5-1.0)·x and the half-height of the fractures c = (0.5-1.0)·h. After the multistage hydraulic fracturing, the wells of upper and lower rows - the production wells are completed and commissioned into production. At each reduction of the oil production rate of the production wells to the values lower than economically reasonable, such wells are stopped, and the middle row wells - injection wells are pumped by gas until the injection pressure increases at least in three times, and then the stopped production wells are allowed to work.

EFFECT: oil recovery of thick solid carbonate oil reservoirs increase.

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