Hydraulic fracture propagation behavior and diversion characteristic in shale formation by temporary plugging fracturing

Abstract

The exploitation of shale oil and gas has become commercial in the Sichuan basin, China. However, initial fracture closure will result in low production. Therefore, temporary plugging fracturing technology is proposed to create new fractures in alternate directions using a temporary plugging agent that blocks initial fractures, which will lead to a complex fracture morphology. The mechanism of temporary plugging and fracture propagation behavior remains ambiguous, even with many successful operations. Hence, five shale outcrops are used to conduct large-size true tri-axial temporary plugging fracturing simulation experiments to study the issues mentioned above. The effects of horizontal stress difference and temporary plugging agent amount on plugging effectiveness as well as fracture propagation behavior are discussed. The results reveal that the initial fractures are sealed successfully by a water soluble temporary plugging agent. Two plugging positions, fracture heel and tip, result in three main fracture diversion patterns: fracture diversion at the old fracture heel, fracture diversion inside the old fracture, and a new fracture induced at a new position. Based on the fracturing pressure curve, fracturing pressure in the second fracturing is higher than that of the first fracturing, which indicates effective plugging and fracture diversion. A large horizontal stress difference has prevented fracture diversion, and led to a small diversion angle. However, it has improved the induced fracture propagation length. Moreover, the temporary plugging agent amount determines the plugging position and fracture diversion pattern. Fracture diversion inside existing fractures is a result of a small amount sealing at the fracture tip. The other two patterns are created by a large amount of plugging at the fracture heel. Therefore, in order to achieve successful plugging effectiveness, it is necessary to conduct more experiments to optimize operation parameters according to the specific horizontal in-stress state.