Oil & Gas Geology ›› 2024, Vol. 45 ›› Issue (6): 1628-1639.doi: 10.11743/ogg20240610

• Petroleum Geology • Previous Articles     Next Articles

Geological characteristics and exploration potential of deep coalbed methane in the slope area of the northeastern Ordos Basin

Shihu ZHAO1,2,3,4(), Zengqin LIU1,2,3,4(), Baojian SHEN1,2,3,4, Bing LUO1,2,3,4,5, Gang CHEN1,2,3,4, Xinjun CHEN1,2,3,4, Jiaqi ZHANG1,2,3,4, Junyu WAN6, Ziyi LIU6, Youxiang LIU6   

  1. 1.State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development，Beijing 102206，China
    2.Key Laboratory of Shale Oil/Gas Exploration and Production Technology，SINOPEC，Beijing 102206，China
    3.Key Laboratory of Deep Coalbed Methane Exploration and Development，SINOPEC，Beijing 102206，China
    4.Petroleum Exploration and Production Research Institute，SINOPEC，Beijing 102206，China
    5.Exploration and Development Research Institute，Jianghan Oilfield Branch Company，SINOPEC，Wuhan，Hubei 430223，China
    6.Wuxi Institute of Petroleum Geology，Petroleum Exploration and Production Research Institute，SINOPEC，Wuxi，Jiangsu 214162，China
  • Received:2024-09-13 Revised:2024-10-16 Online:2024-12-30 Published:2024-12-31
  • Contact: Zengqin LIU E-mail:zhaoshh0310.syky@sinopec.com;liuzengqin.syky@sinopec.com

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Abstract:

In recent years， significant breakthroughs have been achieved in the exploration of deep coalbed methane （CBM） in the Daniudi area， northern Ordos Basin. This study aims to determine the potential for deep CBM exploration in this area. Based on regional geology and data derived from core and maceral observations， scanning electron microscopy （SEM） image analysis， proximate analysis， mercury injection capillary pressure （MICP） analysis， low-temperature liquid-nitrogen adsorption measurements， and CO2 adsorption and methane isothermal adsorption experiments， along with on-site gas content tests， we delve into the geological characteristics of deep coal seams in the Daniudi area in terms of their spatial distribution， lithotypes， coal quality， reservoir properties， and gas-bearing properties. The No. 8 coal seam of the Taiyuan Formation is identified as the dominant coal reservoir in the Daniudi area. The results indicate that this coal seam is consistently distributed throughout the Daniudi area， with a thickness ranging from 2 to 14 m and vitrinite reflectance （Ro） of 1.7 %. Bright to semi-bright coals occur in the upper part of the coal seam as featuring low ash content， indicating high coal quality and providing a material basis for CBM accumulation. The No. 8 coal seam shows well-developed micropores and macropores， with micropores being predominant， accounting for 67.5 %. The bright to semi-bright coals with low ash content therein display high total pore volume， specific surface area of pores， micropore proportion， and porosity. The roof of the coal seam contains thickly laminated limestones and dark mudstones， as characterized by simple structure and low formation water content， suggesting a dry-coal gas-bearing system. With total gas content ranging from 20.3 to 47.1 m3/t and free gas proportion from 33.2 % to 66.2 %， the No. 8 coal seam is rich in both adsorbed and free gases. This coal seam manifests a gas-bearing area of 2 003 km2， CBM resources of 5 422 × 108 m3， and CBM resource abundance of 2.71 × 108 m3/km2. These findings indicate that deep coals in the Ordos Basin are characterized by favorable geological condition for CBM generation， representing a significant exploration and development target.

Key words: isothermal adsorption, free gas content, macrolithotype of coals, exploration potential, deep coalbed methane （CBM）?, Daniudi area, Ordos Basin

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