Experimental investigation into hydraulic fracture geometry and proppant migration characteristics for southeastern Sichuan deep shale reservoirs

Abstract

Difficulties in fracture extension and proppants adding were two key factors that affected the stimulated volume of deep shale reservoir. To clarify the mechanism of hydraulic fracture (HF) propagation and proppants migration, several groups of large-scale true tri-axial fracturing tests with an ingenious method of sand adding were performed utilizing deep Longmaxi shale outcrops from southeastern Sichuan. The interaction behavior between vertical HF and bedding plane (BP) was discussed. The results showed that due to the low bonding strength, the BPs could be easily activated even under high vertical stress difference coefficient. Based on the different influenced degrees of BPs, four types of HF geometries in the vertical direction were observed, that is, transverse HF, horizontal HF, step-shaped HF with fissure opening, and multilateral step-shaped HF network. The migration distance of proppants was limited and almost all the proppants were distributed around the wellbore, thus inducing the formation of multiple secondary HFs. When there are natural fractures (NFs) with large aperture around the wellbore, proppants almost entirely distributed along the NFs. The main factor, causing the difficulty of fracture extension and proppants migration, was the complex HF geometry characterized by the multi-branched fractures with slippage of BPs.