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Research on Optimization of Construction Parameters of Vertical Cross-Layer Fracturing in Thin Interbedded Coalbed
Jie Chen1,2,3, Yanming Zhu1, Linjie Shao4
1School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China.
Abstract:
Thin interbedded coal seams exhibit characteristics of numerous layers, minimal thickness, and a clustered distribution. Horizontal well cross-seam fracturing technology represents an effective approach for coalbed methane exploration and development. However, the adaptability of construction parameters for longitudinal cross-seam fracturing in thin interbedded coal seams remains a critical factor constraining the seamless integration of horizontal wells with coal seam clusters and hindering efficient gas production. This study experimentally analyzed the mechanical characteristics and mineral content of coal and rock based on mechanical properties, mineral composition, and pore structure. A fully three-dimensional, structured grid geological model of the longitudinal multithin interbedded formation was constructed using the GOHFER platform. Crack propagation simulations were conducted, and the parameters for longitudinal cross-bedding fracturing operations were optimized through a five-factor, four-level orthogonal experimental design. Research findings indicate that the compressive strength of the roof and floor strata in coal seams 10# and 12# exceeds that of the coal mixture, exhibiting higher brittleness. The crack pressure for coal seams 10# and 12# ranges between 13.22 and 13.35 MPa. The roof and floor strata contain a high proportion of clay minerals, reaching 62.4-67.7%. When perforation points are located within the roof strata of the lower coal seam, vertical cracks can effectively communicate between the two coal seams. However, when perforation points are situated within the lower coal seam itself, cracks encounter significant difficulty penetrating upward through the intercalated layer, thereby limiting their ability to communicate with the overlying coal seam. Taking into account both the longitudinal layer-penetrating capability of cracks and the convenience of construction organization, the recommended combination of construction parameters is flow rate 14 m3/min + single-stage sand volume 60 m3 + single-stage fluid volume 1700 m3 + perforation count 25 + crack spacing 50 m + two clusters per stage. The research findings provide theoretical reference for optimizing construction parameters in horizontal fracturing operations targeting thin, interbedded, multilayer coalbed methane reservoirs.
