Multi-Scale Hydraulic Fracturing of Horizontal Wells in Deep Shale Gas Plays

Shale gas resources are abundant in shale plays deeper than 3500m in China.They have not been commercially developed yet due to high treatment pressure,difficulty in sand pumping and low post-frac production.Rock mechanics tri-axial tests were conducted under simulated reservoir conditions.Testing results showed that the deep shale plays presented obvious nonlinear deformation feature,which would lead to narrow fracture widths after fracturing.Combining our fracturing experiences in deep shale gas wells fracturing,we put forward the technique of multi-scale fracturing in horizontal wells of deep shale gas plays.This technique adopts acid pretreatment,or acid injection during the treatment,and slit slugging and grinding to reduce treatment pressure;step pump with varied pumping rate and multi-stage alternative pump injection mode with varied frac fluid viscosity to stimulate multi-scale fractures;and increases the portion of small size proppant to realize long-term and effective prop of multi-scale fractures.This technique has been applied in a well in Southeastern Sichuan Basin and achieved encouraging fracturing result.It demonstrates the feasibility and availability of this technique in deep shale gas wells,and fracturing results can be improved from this technique’s application in deep shale plays.