Advances in Technology of CBM Horizontal Well Completion in Deep Area

Abstract

In 2011, a deepest horizontal Coalbed Methane (CBM) well in China, with a total vertical depth in excess of 1100m, was successfully drilled by Shell China E&P Co. Ltd (SCEPCo). The well, located in the East Ordos Basin, achieved a total 'in-seam' length of nearly 3600 m. The integration of technology across multiple disciplines, which enabled this well to be a success, is presented in this paper. An integrated geological evaluation of both regional and block scale data was used to map the depth, continuity, thickness and gas content of the coal seams. This evaluation, together with understanding of structure and distribution of faults, was then used to pick a well location in an area where the coal seams are thick and the gas content is high. The uncertainties in the evaluation are greater where the coal seam is deeper and include factors such as the stress field, coal mechanical properties, structural complexity of the seam, presence of a roof aquifer and the permeability. When planning the drilling of the well, a comprehensive drilling strategy, together with sidetrack and drilling fluid programs were prepared prior to the campaign. This preparation was invaluable for successfully drilling the first horizontal well despite the geological uncertainties present. The MWD technology and expertise in geosteering were also essential to successfully drill the horizontal laterals in this area as there is a potential aquifer in the limestone roof which needs to be avoided and there are kink bands in the coal seams. A geomechanical evaluation was also completed to understand the stress field and the orientation of fractures in the coal seam. This is required to understand and balance the trade-off between orienting the horizontal laterals to maximize production against maintaining the stability of the well bore. After completion of the well, the well production was initially affected by several shut-ins which delayed gas production. A combined dewatering and control system was then adopted which was shown to effectively mitigate fluid level buildup issues arising from unexpected workovers and well shut-ins. In conclusion, this well demonstrated the feasibility of drilling horizontal CBM wells in the area deeper than 1100 m and it is expected that this technology can be applied in the near future to unlock the potential of other deep CBM opportunities in China.

Archives of Mining Sciences

“…By using multi-lateral horizontal wells (Fig. 3) coalbed methane extraction increased from a few to several times, greater flow of methane from coal seams was obtained (Yuan, 2013). Fig.…”