Oil & Gas Geology ›› 2022, Vol. 43 ›› Issue (5): 1013-1023.doi: 10.11743/ogg20220501

• Petroleum Geology • Previous Articles     Next Articles

Progresses and directions of unconventional natural gas exploration and development in the Carboniferous-Permian coal measure strata, Ordos Basin

Xusheng Guo1,2(), Dehua Zhou1, Peirong Zhao1, Zengqin Liu2, Dianwei Zhang2, Dongjun Feng2, Fengcun Xing3,4, Wei Du2, Gang Chen2, Fan Yang2, Chuanxiang Sun2   

  1. 1.China Petroleum & Chemical Corporation,Beijing 100728,China
    2.Petroleum Exploration and Production Research Institute,SINOPEC,Beijing 102206,China
    3.State Key Laboratory of Oil and Gas Reservoir Geology and Exploration,Chengdu University of Technology,Chengdu,Sichuan 610059,China
    4.Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu,Sichuan 610059,China
  • Received:2022-02-17 Revised:2022-07-09 Online:2022-10-01 Published:2022-09-02

Abstract:

With the development and breakthroughs made in sweet spot assessment of unconventional gas, multi-stage hydraulic fracturing in horizontal wells, and simultaneous development of multiple pay zones, the exploration and development paradigm of unconventional gas has shifted from single mode to composite mode. The joint exploration and commingled production of unconventional gases from coal measure strata of marine-to-continental transitional facies is expected to become a new “unconventional revolution” following the shale revolution. The Carboniferous-Permian is of the most important source rock sequences in the Ordos Basin, featuring huge potential in unconventional gas resources, though at the initial stages of exploration and development. Based on exploration progresses made and research results achieved during the 13th Five-Year Plan period, we summarize the geological features of the Carboniferous-Permian coal-measure unconventional gas in the Ordos Basin, that is, “two sources, three highs, and three gases”. The Carboniferous-Permian is dominated by multiple types of lithology or lithological components, and the coal-rich components(“two sources”) are major targets in exploration,among others. The organic macerals of the source rocks are dominated by vitrinite, and organic pores and micro-fractures are the main reservoir spaces, characterized by high total organic carbon content, high thermal maturity, and high gas content (“three highs”). The gas occurrence is markedly differentiated between deep and shallow layers, with adsorbed gases dominating the shallow coal seams, and free gases occurring in the deep coal seams, resulting in the coexistence of coalbed methane, shale gas and tight sand gas (“three gases”), and the existence of their various combinations. Regarding challenges such as tightness of reservoirs, large difficulty in sweet spot identification, and relatively high stresses, we have developed drilling and completion technique of “long lateral, large pumping rate, large liquid volume and high sand load”, which could be of effective supports to breakthroughs made in unconventional gas exploration in deep coal-measure reservoirs. It is suggested to further strengthen the comprehensive research on coal-measure source rocks and lithological assemblages, establish theory and technology for integrated evaluation of geological and engineering sweet spots, and develop supporting technologies in exploration, development, and engineering, in an effort to accelerate high-quality development of unconventional gas in the Ordos Basin during the 14th Five-Year Plan period.

Key words: lithological assemblage, gas-bearing potential, unconventional natural gas, Carboniferous, Permian, Ordos Basin

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