Abstract:

Significant advancements in deep Coal Bed Methane（CBM）development have been achieved through the adoption of reservoir reforming technology, characterized by the utilization of large sand volumes and large fracturing fluid volumes in Yanchuannan CBM Gas Field of Ordos Basin. This study conducts field tests on coal reservoirs with varying fracturing scales to explore the patterns of fracture expansion post-hydraulic fracturing and assesses the resultant reservoir reform areas. The analysis identifies distinct fracture patterns across different types of gas wells and fracturing scales, examines the impacts on gas production post-commissioning, and develops fracturing technology tailored to Yanchuannan CBM Gas Field. Multiple moderate-scale fracturing interventions in inefficient old wells and large-scale fracturing in new wells effectively extend fracture lengths and expand the area of reservoir reconstruction. However, the morphology of the resulting fracture networks varies significantly. Inefficient old wells subjected to multiple medium-scale fracturing develop a “rose-shaped” fracture network with primary and secondary fractures, whereas new wells exhibit a “long elliptical” fracture pattern. Notably, the use of a single ultra-large-scale fracturing fluid achieves greater efficiency, producing longer half-length fractures and larger renovation areas under the same scale. The fracture half-length and renovation area demonstrate a logarithmic increase with the frequency of fracturing, significantly enhancing the efficiency. Economic evaluations of trial production confirm that two large-scale fracturing operations are economically viable, providing a foundation for future well network deployment. Fracturing equipment powered by diesel struggles to adapt to continuous operations at scaled-up levels, suggesting that electric-driven fracturing devices present a reliable alternative for the sustainable development of integrated CBM gas fields. These insights not only enhance understanding of fracture dynamics in deep CBM reservoirs but also guide the optimization of fracturing strategies and equipment choices for future developments.

Key words: Yanchuannan Gas Field, deep CBM, fracturing scale, microseismic monitoring, fracture network pattern