Application of Near-Bit LWD Gamma Image Logging in Horizontal Coalbed Methane Reservoir

For judging the formation lithology accurately, guiding the tool to drill in target reservoir, correcting drilling trajectory timely and improving the encounter rate, a near-bit 16-sector imaging LWD system that can be used in water-base and oil-base drilling fluid is presented in this paper. The LWD system is consisted of near-bit gamma imaging sub, screw and data receiving sub. It can be used in unconventional reservoirs such as shale and coalbed methane reservoir to achieve data measurement and stable transmission of near-bit deviation and gamma-ray. Compared with 8-sector gamma imaging, the application of 16-sector dynamic high-precision gamma scanning imaging technology provides more precise, accurate and timely parameters measurement. The near-bit gamma imaging LWD system has been provided successfully used in coalbed methane reservoir. The field application shows that this system exhibits excellent identification for coal lines and carbonaceous mudstones, and could guide drilling tool back to reservoir in the absence of formation, with the drilling ratio of reservoir by 97%. The application of near-bit gamma imaging LWD system in horizontal coalbed methane lay foundation for the study of dynamic high-precision gamma scanning imaging technology used in unconventional reservoirs.