Drilling and completion technologies for ultra-deep complex gas field in Kuqu depression

Kuqu depression, the main area for natural gas storage and production in Tarim basin, is characterized by the complex geological conditions, such as ultra-burial depth, high pressure, high temperature, compound salt formation, steep gravel bed, multiple pressure system, and unstable formation. Drilling and completion engineering are faced with such problems as lack of well structure, limited acceleration for gravel layer, frequent and complex leakage or collapse for compound salt formation, and poor cementing quality. To solve above problems, five key technologies are formed. Firstly, expansion tube subsidy and three trajectory optimization technologies, optimize the non-standard wellbore structure, and improve the anti-risk ability of deep wellbore. Secondly, the refined characterization of gravel bed and auxiliary technologies, helpfully form the personalized accelerated template and greatly reduce the drilling cycle. Thirdly, the precisely managed pressure drilling and cementing technology has been successfully applied to the strata with narrow mud windows with high density, multiple pressure systems, or simultaneous overflow and leakage, which cuts down the complexity treatment time by more than 80%. Fourthly, the high temperature and high-density drilling fluid and cementing fluid system helps effective drilling and reduces the downhole accidents in complex sections such as high temperature, high pressured saltwater and well leakage. Fifthly, the acid soluble temporarily plugging material used for drilling in the target zone significantly reduces reservoir pollution and the average loss rate by more than 46%. Above achievements can provide support for the fast development of natural gas resources and accelerate the exploration process of the three large gas fields with trillion resources in Kuqu depression.