Experimental study on plugging performance and diverted fracture geometry during different temporary plugging and diverting fracturing in Jimusar shale

Abstract

Temporary plugging and diverting fracturing (TPDF) is one promising technology to form complex fracture networks in unconventional oil and gas resources, such as Jimusar shale in China. The key to the success of this technology depends on two processes: creating a tight plug within previously-created fractures using temporary plugging agents (TPA), and then forming diverted fractures after plugging. Many scholars have studied the plugging law of TPA under different channels aiming at the first process. However, the second process of fracture re-direct to form fracture networks after effective plugging has not been investigated clearly, especially in shale formations. Based on Jimusar shale, this paper investigated the plugging performance of fibers and particles and diverting fracturing behavior under three different TPDF application scenarios: near-wellbore in-plane TPDF, multistage TPDF in the horizontal wellbore, and far-field TPDF within fractures. A series of experiments were carried out under different stress difference conditions and TPA types using true tri-axial fracturing system. Experimental results show that: firstly, in near-wellbore TPDF experiments, the plugging pressure peaks would be increased with horizontal stress difference (HSD) while the deflection angle between the diverted fracture and the initial fracture would decrease with HSD. Once the HSD is over 7.5 MPa, the diverted fractures would be nearly parallel to the initial fractures. Secondly, in far-field TPDF within 2 mm propped fractures, 1 wt% pure fibers cannot form the effective plug in any fractures regardless of the HSD, while the combination of 1 wt% fibers and 1 wt% particles could effectively plug all fractures. The diverted fractures could be only created as branch fractures at the middle of the initial fractures, but the diverted fractures would be merged into the initial fractures when HSD is over 7.5 MPa. Thirdly, in multistage TPDF in the horizontal wellbore, the initial fracture almost initiates from only one slot and becomes one transverse fracture, but multiple parallel transverse fractures after plugging could happen but not always occur. The diverted fracture may also form a longitudinal fracture under low HSD because the slots have been plugged by TPAs. In addition, influenced by bedding and natural fractures, more bedding fractures are activated after plugging, which forms a more complex fracture network. Our experimental results could deepen the understanding of TPDF in Jimusar shale reservoir and also provide fundamental for field design in similar shale reservoirs.