Gas expansion caused by formation uplifting and its effects on tight gas accumulation: A case study of Sulige gas field in Ordos Basin, NW China

Abstract

Gas expansion caused by significant exhumation in the Sulige gas field in the Ordos Basin since Late Cretaceous and its effects on hydrocarbon accumulation have been investigated systematically based on comprehensive analysis of geochemical, fluid inclusion and production data. The results indicate that gas volume expansion since the Late Cretaceous was the driving force for adjustment and secondary charging of tight sandstone gas reservoirs in the Sulige gas field of the Ordos Basin. The gas retained in the source rocks expanded in volume, resulting in gas re-expulsion, migration and secondary charging into reservoirs, while the gas volume expansion in the tight reservoirs caused the increase of gas saturation, gas-bearing area and gas column height, which worked together to increase the gas content of the reservoir and bring about large-scale gas accumulation events. The Sulige gas field had experienced a two-stage accumulation process, burial before the end of Early Cretaceous and uplifting since the Late Cretaceous. In the burial stage, natural gas was driven by hydrocarbon generation overpressure to migrate and accumulate, while in the uplifting stage, the gas volume expansion drove internal adjustment inside gas reservoirs and secondary charging to form new reservoirs. On the whole, the gas reservoir adjustment and secondary charging during uplifting stage is more significant in the eastern gas field than that in the west, which is favorable for forming gas-rich area.

Keywords

• uplifting erosion and unloading
• abnormal pressure
• gas volume expansion
• adjustment of gas reservoir
• secondary charging
• two-stage accumulation