关键词: 鄂尔多斯盆地东缘, 深部煤层气, 重大突破, 技术创新, 生产特征, 挑战与对策

Abstract: As an important alternative energy in the unconventional oil-gas field, coalbed methane (CBM) has enormous potential. The deep coal seams are developed on a large scale in Ordos Basin. However, CBM exploration and development is restricted due to complex geological and engineering conditions in the eastern margin of the basin. This paper is a case study of Linxing-Shenfu block in Ordos Basin. The scientific issues such as geological characteristics of sedimentation and hydrocarbon accumulation, production characteristics, and fracturing mining technology regarding deep coal seams in Ordos Basin are explored based on a large amount of drilled data, core analysis data, and drainage dynamic data. The results show as follows:both semi-bright and semi-dark coal in deep coal seams are developed, dominated by primary structure; the deep CBM is characterized by high gas saturation, sufficient reservoir energy, and favorable coal body structure; two core indicators for evaluating sweet spot area of deep CBM have been determined, i.e., resource availability (coal reservoir energy) and feasibility of fracturing (structure, vertical fracture zone, stress difference between roof and floor and coal seam); a new method has been established by quantification of fractal theory and numerical simulation to characterize the complexity of fractures, forming a horizontal well segmented extreme volume fracturing technology system featured with "dense cutting+large displacement+combined proppant+pre-positioned acid+variable viscosity slickwater"; two gas production control parameters (gas saturation and gas content) have been determined for deep coal seams, and production wells can be divided into three categories based on the characteristics of gas production, i.e., self-flowing after pressure, immediate gas production after discharge, as well as conventional discharge and production. The large-scale efficient development of deep CBM needs to tackle a number of fundamental problems. Great efforts should be paid on making a breakthrough in hydrocarbon expulsion and occurrence process of deep coal seams, determining the boundary conditions for the enrichment area of sweet spots, studying the mechanical properties of deep coal seams and volume transformation. Moreover, it is required to continuously strengthen the integrated technical management of geology, engineering, drainage and production, innovate the enterprise-locality integration and management patterns, and keep improving the assessment of the ultimate recoverable reserves of a single well, so as to achieve the large-scale beneficial development of deep CBM.

Key words: eastern margin of Ordos Basin, deep coalbed methane, major breakthrough, technological innovation, production characteristics, challenges and countermeasures