Drilling and Completion Technologies for of Geothermal Wells with Medium and Low Temperatures

To enhance the engineering quality of geothermal wells and to obtain desirable single well productivity,geothermal drilling and completion technologies have been optimized,and developed casing program with two sections suitable for geothermal development in sandstone formations and three sections suitable for matrix formations.Hanger connections,together with sealing by cementing slurry in overlapping sections have been developed to eliminate possibility of water channeling in bottom sections of the pumping chamber.In addition,design parameters for perforated PVC pipe,wire-wrapped screens and slotted liners are optimized to satisfy the demand of completion in different formations and different areas.Four drilling techniques,including mud circulation drilling,freshwater circulation drilling,gas-charged water circulation drilling and gas-lifting reverse circulation drilling,have been developed for thermal reservoir susceptible to lost-circulation.According to the requirement of production,logging parameters,cementing and integral flushing technologies in geothermal wells have been specified.The newly developed technologies have been deployed on site of the Well Qingfeng XBXZ-1,with multistage pump testing water for 24 h,flow rate of 120 m3/h,water temperature of 68℃,the static liquid level being 15.50 m,the dynamic liquid level being 48.00 m.Successful drilling and completion technologies for geothermal wells at medium or low temperatures can effectively eliminate severe lost circulation,fast drop in water levels,undesirable settling of cuttings,channeling of water between target formation and surface layer,etc.It has bright prospects in promotionand application.