The Gulu geothermal field is a typical hydrothermal high temperature geothermal field in the Naqu-Nimu geothermal belt of Xizang.The safe,economical,and efficient drilling technology largely determines the potential for the development and utilization of its high-temperature geothermal resources.ZK401 well is a high-quality and high-yield exploration and production combined well implemented in the Gulu geothermal field.The rock is mainly composed of granite,which has high rock hardness,low mechanical drilling speed,and short drill bit service life.Multiple layers of thermal storage were exposed from top to bottom,and the medium temperature geothermal fluid of 124.8℃was exposed from depth 35 to 41 m,and the total amount of steam and water is about 40 t·h-1.The medium temperature thermal storage of more than 120℃was exposed at the depth of 50 to 320 m,and the total amount of steam and water is about 30 to 35 t·h-1.320 to 1 320 meters exposed 186.9℃high-temperature thermal storage,with a total amount of steam and water of up to 348 t·h-1.It has the characteristics of shallow thermal storage depth,high temperature,developed fault structures,and large formation water output.High temperature and water invasion can easily cause drilling fluid failure,high risk of blowout,and difficulty in safe drilling.In order to solve the above difficulties in drilling construction,the key technologies of high-temperature geothermal drilling were studied.Through the use of special-shaped PDC bit and rock thermal cracking technology,the penetration of a single special-shaped PDC bit was increased by 23%～48%compared with the same size cone bit,and the average mechanical drilling speed of the granite in the third drilling has been increased to 3.18 m·h-1.By optimizing the wellbore structure,adopting simple pressure control drilling technology,and using low-temperature clean water as as circulating drilling fluid for second and third drilling,the purpose of timely discovering and effective protection of thermal reservoirs and control of blowout risks has been achieved.The ZK401 well has achieved safe and continuous drilling under harsh conditions of exposing 186.9℃high-temperature thermal storage at 520 m and a total steam and water of 348 t·h-1.The non production time has been shortened by 37%compared to adjacent wells using conventional drilling techniques,which greatly reduced drilling costs and improved the potential for the development and utilization of high-temperature geothermal resources,this provide reference for solving the drilling construction of high-temperature geothermal wells in the region and even other regions in the future.
Gulu geothermal fielddrilling technologysimple press-control well drillinghigh-temperature geothermal wellblowout
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