Analysis on influencing factors of single/multi-layer development of coalbed methane field: A case study of Baode Block

Baode Block in the eastern margin of Ordos Basin is the first coalbed methane field of middle-low rank coal with 500 million cubic meters of production capacity constructed and reached in China, and it is also a benchmark in the coalbed methane industry there. During the development of Baode Block, good results are obtained by the commingled development of two sets of main coal layers, which are better than that of single-layer development. However, poor development result is obtained locally in the commingled development of some wells under the same development conditions, which is poorer than that of single-layer development. Therefore, overall evaluation was performed for Baode Block from the points of geological conditions, gas reservoir characteristics and gas production of the single/multi-layer commingled development wells in each coal bed. According to the research, the geological conditions of coalbed methane are the essential factors to control the result of single/multi-layer commingled production, which will control the CBM reservoir and influence the CBM production together with the reservoir. Herein, the difference in the effect of single/multi-layer drainage was determined in accordance with the main quantitative indicators, and the optimal quantitative evaluation indicators of single/multi-layer development of coalbed methane were determined by preferentially selecting 1 set of coal layers. That is, the original formation pressure difference is not more than 0.6 MPa, the critical desorption pressure difference is less than 0.4 MPa, and the permeability difference is within 2×10⁻³ μm² for the two sets of coal layers, which are suitable for commingled development of coalbed methane. On this basis, the region for development in next step and the key areas for development adjustment were pointed out. Definitely, it is more favorable to give priority to the single-layer development for No.8+9 coal layers in the western part of Unit 1 and in the central and western parts of Unit 2 in the block, as well as No.4+5 coal layers in the southern part of Unit 3. In view of the area with a large amount of undeveloped reserves in No.8+9 coal layers in the block, No.8+9 coal layers may be developed in priority by adjusting the development sequence of layers, with No.4+5 coal layers blocked temporarily. In general, the results of this research are of great significance for the guidance of efficient development of coalbed methane fields with multiple bed series.