Improving the efficiency of hydraulic fracturing in wells with depleted gas reservoirs

Abstract

The reasons for the low production rate of gas wells in depleted gas reservoirs are presented, including low natural permeability of productive formations and contamination of the bottomhole zone with solid phase and liquid. The methods of gas inflow stimulation to the bottom of wells are presented, among which hydraulic fracturing (HF) is worthy of attention for low permeability formations and deterioration of the bottomhole zone. The essence of hydraulic fracturing is described. Conventional and high-power hydraulic fracturing, its technology, scope, materials and chemicals used, and technological efficiency are characterized. During hydraulic fracturing in wells at depths of more than 600 m, to which the main proven gas reserves are confined, vertical and near-vertical fractures will mainly form. With a small reservoir thickness, vertical fractures can damage the cement stone behind the production casing, which in depleted gas reservoirs will help create conductive channels from the gas reservoir to the upper horizons. With a vertical fracture, gas flow to the well will be in one direction along the fracture and other volumes of the wellbore zone within the fracture radius will not be fully covered by filtration. To improve the efficiency of hydraulic fracturing in wells in depleted gas reservoirs, it is proposed to create a horizontal fracture in thin formations or several vertical fractures in formations of large thickness by preliminary hydraulic sandblasting perforation (HSP) or gas hydrosandblasting perforation (GHBP). When preliminary creating horizontal channels in the bottomhole zone, tubing with a perforator is gradually rotated to a certain angle, and when creating vertical channels, they are gradually raised to a certain height. After the perforation channels are created, hydraulic fracturing is performed. With the sequential use of hydraulic sandblasting perforation and hydraulic fracturing, it is possible to create a grid of cracks of increased length in the bottomhole zone in the specified directions. Using known analytical dependences, the length of individual perforation channels during gas-hydro-sandblasting perforation with a nozzle diameter of 4.5 and 6 mm in the perforator and the fracture radius during hydraulic fracturing were determined. The degree of increase in gas flow rate separately from hydraulic fracturing and hydraulic fracturing from their sequential implementation is estimated