Technology and Application of CQ-SHIELD Micro-crosslinked Drilling Fluid in Deep CBM Horizontal Wells of Changqing Region

The Benxi 8# deep coalbed methane (CBM) reservoir as a key development target in the Changqing region, features deep burial depth and substantial resource potential, making it a crucial stratigraphic horizon for China's recent natural gas development. However, the complex geological conditions of deep CBM formations - including intricate in-situ stresses, developed bedding planes and micro-fractures, widespread coal-shale interbeds, and strong heterogeneity - have led to frequent wellbore collapse and stuck pipe incidents, posing major technical challenges for safe and efficient drilling in deep CBM wells. This study first clarifies the dominant controlling factors of wellbore collapse in coalbed methane horizontal wells through comprehensive analysis of mineral composition, physicochemical properties, and microstructure characteristics of deep coal-measure formations in the Changqing region. A targeted solution was developed: the CQ-SHIELD micro-crosslinked strong plugging anti-collapse drilling fluid technology specifically designed for deep CBM horizontal wells. This innovative fluid demonstrates superior performance with API fluid loss ≤ 3 mL and HTHP fluid loss ≤ 10 mL, showing over 40% improvement in comprehensive plugging capability compared with conventional drilling fluids. Through field applications in over 60 deep CBM horizontal wells across various regions of the Ordos Basin, the authors systematically analyzed existing technical challenges including excessive fluid density, high operational costs, frequent coal-shale interbed collapses, and completion difficulties. The paper further investigates fundamental theories regarding fracture propagation and slippage patterns at coal/gangue interfaces, presents the CQ-SHIELD micro-crosslinked drilling fluid system, and evaluates its application effectiveness in deep CBM development through complex incident reduction and cost efficiency improvement analyses.