Practice and understanding of coalbed methane co-production in Zhijin area, Guizhou

Guizhou Province is a typical area where thin-to-medium thick coalbeds are developed, where the resource endowment characteristics, including multiple coalbeds, small thickness, low permeability, high in-situ stress and multi-layer superposition of pressure system, lead to the difficulties in localization of the mainstream technologies at home and abroad for the development of coalbed methane (CBM) and the utilization of CBM resources. The particularity of these geological characteristics of the multiple and thin CBM determines the obvious selectivity of technologies for its development, and thus the co-production of multiple coalbeds becomes the essential method for effective development and utilization of CBM resources in the area. Since 2009, 23 coalbed methane wells have been successively deployed in Zhijin area by SINOPEC East China Oil & Gas Company, realizing the maximum daily single-well output of 5 000 m³ and the average daily single-well output over 1 000 m³ in the test well group (10 vertical wells). Therefore, the geological conditions for accumulation of coalbed methane in multiple thin layers in this area were systematically analyzed based on the exploration and development practice of coalbed methane in multiple layers in Zhijin area, and the geological applicability of the key development technologies was summarized. Finally, the following understandings were obtained from the aspects of geological layer selection, development mode and drainage control method: (1) The discrimination method for optimization of co-production layers was established, the optimal horizon combination dominated by No.20, No.23, No.27 and No.30 coalbeds in coal formation Ⅲ in Zhuzang subsyncline was defined for co-production. (2) The featured development mode combining the separate pressure co-production in directional wells and the volume stimulation by staged fracturing in horizontal wells was formed. (3) The refined drainage and production control system was formulated based on the concept of “balanced drainage and gradient pressure reduction” for the purpose of “area pressure reduction”. The research results are helpful to promote the development of multi coalbed methane in this area, and have important reference value for the efficient development of coalbed methane in Guizhou Province.