Abstract: It has been known that CBM exploration is predominant in the Jinxi flexural fold belt in the eastern margin of Ordos Basin.However, due to unclear understanding of gas accumulation, there has been no major breakthrough of tight gas exploration. In 2013, CNOOC made a firm decision to shift from CBM exploration to tight gas exploration. By systematically summarizing the gas accumulation condition and gas reservoir characteristics, the company revealed the differential enrichment law of tight gas, proposed favorable areas and obtained tight gas reserves. The research result suggests that: (1) Pay zones of Linxing-Shenfu Gas Field are mainly in the Carboniferous Benxi Formation and Permian Taiyuan and Shihezi Formations, which are typical tight sandstone gas reservoirs; (2) The main source rocks are coal measure strata, with an average CH4 content of 95% and no H2S; (3) The burial depth of gas reservoir is between 1300-2200 m, and the pressure coefficient ranges from 0.85-1.01; (4) The reservoir consists of widely spread delta sandstone and barrier bar sandstone, of which the former has an average porosity of 8.8%, permeability of 1.10 mD, and pore throat radius less than 1.5 μm, while the latter has an average porosity of 7.6%, permeability of 0.59 mD, and pore throat radius less than 1.1 μm; (5) Influenced by the Lishi strike-slip fault zone in the east and the Zijin Mountain volcanic activities in the south, fault activity is strong in the east and weak in the west, while strong in the south and weak in the north. The hydrocarbon generation intensity is high in the south and gradually decreases towards the north affected by volcanic activities;(6) The study area experienced three periods of tectonic movement after hydrocarbon generating in the Late Jurassic, and the gas reservoir is dominated by vertical migration and accumulation. In Lingxing block, gas reservoir is mainly inside the source, near source and far source accumulation, whereas in Shenfu block it is mainly inside source and supplemented by near source accumulation with smaller scale of gas reservoir; (7) Three sets of key exploration technologies have been developed, which provide solid technical support for tight gas exploration and development. Until 2021, the proven natural gas reserves in Linxing-Shenfu block are 1010×108 m3 guided by above knowledge and technology and another one hundred billion cubic meters of geological reserves could be increased with the progressive exploration from south to north.

Key words: northeastern margin of Ordos Basin, Linxing-Shenfu Gas Field, tight sand gas, gas enrichment law, key technology