The effect of the fracture geometries from different stratification angle on the imbibition recovery of Jimusar shale oil: A comprehensive experimental study

Abstract

Hydraulic fracturing technology is one of the most effective stimulation means in the development of shale oil. Due to the stratification structure of shale, the fracture geometries after hydraulic fracturing will be seriously affected by the stratification angle, which will further effect the imbibition recovery of shale oil. At present, scholars have carried out a large number of research on the influence of stratification angles on fracture morphology. However, few scholars have studied the influence of fracture morphology on imbibition recovery under different stratification angles. Based on the Jimsar shale, this paper comprehensively explored the fracture morphology under four stratification angles and its influence on imbibition recovery. Twelve shale cores were subjected to true triaxial compression test, non-destructive CT scan and NMR-based imbibition test to obtain acoustic emission signals and energy during fracturing, quantitative information of CT scan fracture morphology and corresponding imbibition recovery. The results showed that, first of all, shale rock samples with stratification angles below 30° have strong brittle failure characteristics under 0 MPa confining pressure. When the stratification angle is higher than 60°, the brittleness of the rock sample is weakened under 20 MPa confining pressure. Secondly, when the confining pressure is 0 MPa and 10 MPa, the fracture volume decreases first and then increases with the increase of stratification angle, showing a “V” shape change rule. When the confining pressure is 20 MPa, the fracture volume decreases with the increase of stratification angle. At the same time, the imbibition experiment verifies that the oil recovery of rock sample with dominant seepage channel is 47.61% higher than that without dominant seepage channel. Finally, for shale reservoirs, hydraulic fracturing perforation along the angle of stratification development can effectively improve the efficiency of energy utilization, increase the effective fracture volume of fracturing, and further improve oil recovery.