Xinjiang Petroleum Geology ›› 2025, Vol. 46 ›› Issue (1): 121-126.doi: 10.7657/XJPG20250115

• APPLICATION OF TECHNOLOGY • Previous Articles    

Effectiveness Evaluation of Tight Sandstone Reservoirs Based on NMR Logging

MU Qian(), LI Gaoren(), ZHANG Wenjing, CHI Ruiqiang   

  1. PetroChina Changqing Oilfield Company, a.National Engineering Laboratory for Exploration and Development of Low Permeability Oil & Gas Fields; b.Research Institute of Exploration and Development, Xi’an, Shaanxi 710000, China
  • Received:2024-04-30 Revised:2024-06-14 Online:2025-02-01 Published:2025-01-24

Abstract:

In the Zhijing-Ansai area of the Ordos Basin, the reservoirs in the 8th and 9th members of the Upper Triassic Yanchang formation (Chang 8 and Chang 9 members) are tight, with complex pore structure and unclear vertical distribution of effective reservoirs. A method for evaluating the effectiveness of the tight sandstone reservoirs was proposed based on nuclear magnetic resonance (NMR) logging data and mercury injection data of rock samples. For wells with NMR logging data, the proportions of macropores, mesopores, and micropores can be directly obtained from the NMR data, and an NMR logging-based three-pore component index can be constructed. For wells without NMR logging data, the pore throat radius index can be established by using the relationship between NMR transverse relaxation time and pore throat radius. Both the NMR logging-based three-pore component index and the pore throat radius index can quantitatively characterize the pore structure of tight sandstone reservoirs. Integrating with analysis of formation test data, it is found that single-well liquid production index per meter is positively correlated with pore structure. Thus, an effectiveness evaluation standard for tight sandstone reservoirs was established. The application of this standard to the Chang 8 and Chang 9 members in the Zhijing-Ansai area demonstrates excellent results, with significantly improved accuracy of well logging interpretation.

Key words: Ordos Basin, Zhijing-Ansai area, Yanchang formation, tight sandstone, NMR, pore structure, reservoir effectiveness

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