Impact of fracturing liquid absorption on the production and water-block unlocking for shale gas reservoir

Abstract

A large amount of liquid is pumped into the shale gas reservoir during hydraulic fracturing, and the fluid flowback ratio is usually low. However, field experience showed that the liquids did not cause severe damage to shale gas reservoir. It is urgent to clarify the water block unlocking mechanism of a shale gas reservoir. This work is to discuss the water block unlocking mechanism in shale gas reservoir. Based on the characteristic study of shale gas formation, the fracturing fluid absorption mechanism, absorption ability and impact on shale gas formation damage are systematically studied. Study shows that ultra-low water saturation, abundant micro-to nanotubulars and a huge contact area are the control factors for strong fluid absorption ability of gas-shale. The strong water absorption capacity of the shale gas formation matrix is a key factor in removing water block. Organic matter also has an important influence on absorption ability and gas production. A conceptual evaluation criterion for water block unlocking is proposed based on core absorption capacity, original water saturation and fracture density. The shut-in after hydraulic fracturing is beneficial to gas production and can reduce water production for certain shale gas reservoir.