A new attempt of a CBM tree-like horizontal well: A pilot case of Well ZS 1P-5H in the Qinshui Basin

Abstract

A multi-lateral horizontal well is one of the main well types employed in the coal bed methane (CBM) development. In a traditional CBM multi-lateral horizontal well, either a major hole or laterals will go crossing through coal beds to the largest extent, which may eventually result in bed collapse, footage failing to meet the design requirement, and the major hole unable to be monitored, re-entered and flushed. Therefore, this paper puts forward a design idea of a tree-like horizontal well composed of a major hole (for dredging passage), laterals (for controlling drainage area) and sub-laterals (for enhancing production). The major hole is usually drilled on the stable roof or floor of a coal bed, laterals are drilled from the major hole into coal beds, and several sub-laterals are drilled from laterals. The major hole, laterals and sub-laterals constitute a tree-like drainage and recovery system, whose major hole remains stable for a long period and can be monitored and maintained. The technique has been successfully applied in Well ZS 1P-5H in the Qinshui Basin, Shanxi. The well included one major hole, 13 laterals, and 26 sub-laterals, with a total drilling footage of 12288 m, a total coal bed footage of 9512 m, and a total pure coal footage of 9408 m. Its major hole was fully placed in the mudstone of the coal bed roof. This well records a successful case of incident-free single well drilling with a footage of more than 10,000 m and serves as a new well type for efficient CBM development in China.