Fracturing Pressure Reducing Technique for Shale Gas Well in the Southeastern Sichuan

In order to effectively stimulate the ultra-deep shale reservoirs in southeastern Sichuan and minimize the fracturing pressure,some technical solutions were proposed,such as optimization of perforation parameters,acid pretreatment before fracturing,design of slick water system with high friction reducing rate,and application of lead silt slug techniques.Through analysis and calculation,it was decided to use the φ89 mm perforating gun with type SDP40HMX28-8 charges for perforation at 18 shots/m and phase 60°.Based on core dissolution tests and characteristics of such ultra-deep shale reservoirs,a formula of 15.0% HCl+1.5% HF+2.0% HT corrosion inhibitor+1.5% ferric ion stabilizer was determined.According to the stratigraphic characteristics,a laboratory experiment was performed and it revealed a slick water system consisting of 0.2% efficient friction reducer SRFR-1+0.3% compound anti-swelling agent+0.1% compound synergist + 0.02% defoamer,which is stable and easy to flowback,with viscosity of about 9-12 mPa·s,friction reducing rate than 75% and formation damage less than 10%.Field application showed that the optimized perforation parameters could meet the requirement for perforation friction reduction;acid pretreatment before fracturing enabled the pressure reduced by 10-15 MPa;the lead silt slug technique could effectively reduce the friction due to fractures curvature,thereby reducing the fracturing pressure.It showed that these technical solutions could help to reduce the fracturing pressure in ultra-deep shale gas wells in the southeastern Sichuan.