Case Study—Investigating Probable Root Causes Behind Consistent Higher Water Cut in a Mother CBM Well than its Deviated Wells:Well Spacing,Well Stimulation,and Overlying Strata Viewpoints and Recommendations

摘要

Production from coalbed methane(CBM)reservoirs can often be challenging,particularly related to the dewatering process. Improper positioning and completion of wells can lead to increased complications during the production phase.Additionally, consistently high water levels(undeclined static reservoir pressure)can impede gas production.This paper describes well and production information from the Raniganj coal block. The pad completion discussed has a mother vertical well(V-well)in which three main coal seams were completed(of the total five main seams with interspersed local seams),and dewatering commenced in 2009.At the end of 2011,encircling the V-well,four deviated wells(D-wells)at different azimuths were positioned at horizontal closures of 263 to 364 m from the bottom seam of the V-Well,wherein five main coal seams,along with interspersed local seams,were completed and scheduled for dewatering in mid-2012.Despite consistent high water production rates from the V-Well,the water levels in the V-Well stood consistently higher(rising upward)than the water levels in the D-wells,unlike nearby V and D-well pads. Well spacing information,well stimulation plots,perforation plans,and overlying strata for all five wells on this pad were studied and conclusions were drawn.This paper discusses such conclusions as well as the analyses performed to understand these issues.An attempt has also been made to best optimize hydraulic fracturing(HF)treatment designs to obtain the maximum benefits from stimulation operations. The results reported in this paper will influence the operator’s cost optimization,which could be a major positive influence on the low-cost CBM market in addition to increasing efficiency of the entire operation.