Construction technology of dual horizontal wells for geothermal energy in the coalfield fire area of Liuhuanggou， Xinjiang

Abstract:

This study is set against the background of coal fire control in Xinjiang. Drawing on international engineering experience with closed-loop geothermal systems （CLGS） such as Eavor-Loop， it aims to achieve dual objectives： extracting underground thermal energy to cool coal fire zones， thereby facilitating the recovery of coal resources in burned-out areas， and utilizing the geothermal energy obtained. A closed dual horizontal well heat extraction scheme was adopted， featuring a five-section well trajectory design- "build-up+tangent+horizontal+build-up+tangent". In response to the high-temperature and fractured formation characteristics of the coal fire area， an innovative "small-diameter pilot hole+large-diameter back-reaming" process was employed during implementation. This approach proposes an efficient and low-cost drilling and heat extraction technical solution suitable for high-temperature rock mass underground thermal energy reservoirs in the Liuhuanggou coalfield fire area. In order to solve the problems of high temperature （>170 ℃）， unstable strata and large inclination in the whole well， various drilling and completion techniques are adopted， the drilling fluid system and equipment are optimized， and the high temperature measuring instruments and downhole power tools are applied. As a result， issues such as loose and fractured formations， lost circulation， and abnormal high temperatures when drilling through the coal fire zone were successfully resolved. This work establishes a replicable technical paradigm for future drilling and completion operations in coal fire areas.