Identification of Fluid Interference in Coalbed Methane Co-production Based on Produced Water: A Case Study in the Hancheng Block, Southeastern Ordos Basin, North China

Co-production can improve coalbed methane (CBM) development efficiency under multi-coal seam conditions; however, differences in hydrodynamic conditions between coal seams lead to fluid interference and thus low gas production. Fluid interference identification is important to increase CBM co-production efficiency. In this study, produced water samples were collected from CBM wells in the Hancheng block and their ionic and isotopic compositions were tested to investigate their relationships with productivity and to identify their implications for hydrodynamic conditions and fluid interference in CBM co-production. The produced water samples (PWS) were dominated by Cl, HCO 3 , and Na, with water qualities of Na–HCO 3 and Na–Cl. The PWS of Nos. 3, 5, and 11 coal seams exhibited increasingly enhanced marine influence successively. The PWS from Nos. 3 + 5 and Nos. 3 + 11 coal seams were characterized by continental influences, and the PWS from Nos. 5 + 11 coal seams were characterized by marine influence. The gas production tended to increase with increase in marine influence on produced water. Sensitive indicators and their critical values were extracted to identify the hydrodynamic conditions of the production layers, including Cl (1000 mg/L), Na (1000 mg/L), δ D (− 78.72 %), δ 18 O (− 11 %) and Sr (5 mg/L). The Shanxi and Taiyuan Formations have different hydrodynamic conditions, resulting in poor CBM co-production compatibility. Nos. 5 and 11 coal seams had good co-production compatibility. The results will improve the method of identifying fluid interference during CBM co-production based on produced water analysis.