Supercritical CO₂-driven intersections of multi-well fracturing fracture network and induced microseismic events in naturally fractured reservoir

Abstract

PurposeSupercritical CO2 (SC–CO2) fracturing is a potential technology that creates a complex fracturing fracture network to improve reservoir permeability. SC–CO2-driven intersections of the fracturing fracture network are influenced by some key factors, including the disturbances generated form natural fractures, adjacent multi-wells and adjacent fractures, which increase the challenges in evaluation, control and optimization of the SC–CO2 fracturing fracture networks. If the evaluation of the fracture network is not accurate and effective, the risk of oil and gas development will increase due to the microseismicity induced by multi-well SC–CO2 fracturing, which makes it challenging to control the on-site engineering practices.Design/methodology/approachThe numerical models considering the thermal-hydro-mechanical coupling effect in multi-well SC–CO2 fracturing were established, and the typical cases considering naturally fracture and multi-wells were proposed to investigate the intersections and connections of fracturing fracture network, shear stress shadows and induced microseismic events. The quantitative results from the typical cases, such as fracture length, volume, fluid rate, pore pressure and the maximum and accumulated magnitudes of induced microseismic events, were derived.FindingsIn naturally fractured reservoirs, SC–CO2 fracturing fractures will deflect and propagate along the natural fractures, eventually intersect and connect with fractures from other wells. The quantitative results indicate that SC–CO2 fracturing in naturally fractured reservoirs produces larger fractures than the slick water as fracturing fluid, due to the ability of SC–CO2 to connect macroscopic and microscopic fractures. Compared with slick water fracturing, SC–CO2 fracturing can increase the length of fractures, but it will not increase microseismic events; therefore, SC–CO2 fracturing can improve fracturing efficiency and increase productivity, but it may not simultaneously lead to additional microseismic events.Originality/valueThe results of this study on the multi-well SC–CO2 fracturing may provide references for the fracturing design of deep oil and gas resource extraction, and provide some beneficial supports for the induced microseismic event disasters, promoting the next step of engineering application of multi-well SC–CO2 fracturing.