Laboratory analysis of liquid injection method on hydraulic fracturing initiation and propagation in deep shale formation

Abstract

Compared with the middle-shallow shale gas reservoirs, deep shale formation often reveals lower fracture complexity, smaller effective stimulated volumes, lower conductivity, and faster declined when the same injection model and technical parameters were used. Therefore, it is necessary to research a special injection model for the deep shale formation. In this paper, a series of laboratory stimulated experiments were carried to analyze the injection method on hydraulic fracturing initiation and propagation in the deep shale formation. The outcrop shale of Longmaxi formation in Sichuan Basin was selected and three different injection methods (constant, stepped-rise and cyclic progressive uplift pump rate) were used in these experiments. The test results showed that the stepped-rise pump rate is conductive to opening the pre-existing natural fracture and bedding planes, the fracture complexity of this injection method is the highest. Meanwhile, the fracturing pressure and total injection volume are the lowest. In contrast, the cyclic-uplift injection method can only form a transverse fracture, and the fracturing pressure is the highest. The research results have an important theoretical guiding value for deep shale hydraulic fracturing operation.