Lost circulation prevention and plugging technology for test wells at low pressure fractured formations of the Xiangguosi Underground Gas Storage

Xiangguosi Gas Storage is the first underground gas storage(UGS)in Sichuan and Chongqing area,which is transformed from a depleted carbonate gas reservoir.Due to tectonic activity and erosion,the Lower Triassic Jialingjiang and the Lower Permian Maokou Fms limestones started to expose at the surface;and because of the depleted Permian and Carboniferous gas reservoirs,the formation pressure coefficient is so low and longitudinal pressure system is so complicated that the lost circulation control is the focus of drilling the test wells in constructing this underground gas storage.In view of this,combining leak protection and plugging technologies at home and abroad,we proposed the following technical measures:optimizing low-pressure well intervals to ensure the final effects of different leak prevention and plugging measures;applying gas drilling technology at upper low-pressure sections with fractures developed;employing the HHH plugging technology in drilling fluids at well sections in Changxing– Maokou Fms,and using the Neotoy pressure bearing plugging technology in casing cementing operation at oil-bearing layers.The practice shows that those technologies can not only prevent the lost circulation in the Xianguosi test wells,but greatly improve the penetration rate and reduce the drilling cycle,which provides robust technical support for follow-up similar projects.