CHARACTERISTICS OF GAS ACCUMULATION IN A LESS EFFICIENT TIGHT-GAS RESERVOIR, HE 8 INTERVAL, SULIGE GAS FIELD, ORDOS BASIN, CHINA
Ding Xiaoqi1, Yang Peng2,3, Han Meimei3, Chen Yang3,4, Zhang Siyang5, Zhang Shaonan2, Liu Xuan1, Gong Yiming1, A.M. Nechval4
1State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Sichuan 610059, China
2Northwest Petroleum Bureau of Sinopec, Xinjiang 830011, China
3State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Sichuan 610500, China
4Teaching and Research Office of Oil and Gas Engineering, Ufa State Petroleum Technological University, Ufa, 450062, Russian
5Department of Geology, University of Regina, Regina s4s 3x3, Canada
Keywords: tight gas, gas-water distribution, reservoir, heterogeneity, He 8 interval, Sulige gas field Ordos Basin
Abstract
Because of the lack of gas supply from source rocks and gas loss, inefficient tight-gas fields represent a high share of all gas reservoirs in China. These gas fields are characterized by low abundance and large gas reserves. Here, the He 8 tight-gas reservoirs in the western region of the Sulige gas field are used as an example to characterize gas distribution under conditions of less efficient charging. Results show the following characteristics. First, the sandstone densification process has a relatively large impact on the charging of gas. Litharenite was already subjected to densification at the time of large-scale gas charging, and this was not conducive to gas charging. On the contrary, for sublitharenite, although strong compaction has already occurred during gas generation, quartz overgrowth that leads to further densification of the gas reservoirs occurs simultaneously with large-scale gas charging. This facilitates gas charging, and is characterized by concomitant densification and reservoir formation. Second, structure traps can control the accumulation of gas to a certain extent. In particular, when physical properties of sandstones within the structure traps are appropriate, gas saturation during gas charging can be increased by approximately 7%. Third, less efficient charging is the main cause of the complex gas and water distribution in the He 8 gas reservoirs. The strong heterogeneity of the reservoirs and the decline in the gas reservoir pressure caused by tectonic uplift in the Yanshan period further exacerbate the complexity of gas and water distribution. These factors ultimately caused the He 8 gas reservoirs to become a multireservoir gas field with several gas-water interfaces. He 8 gas reservoirs are neither conventional gas nor continuous gas reservoirs. Rather, they are quasi-continuous gas reservoirs, and the accumulation of gas is controlled by both the top surface of sandstone and physical properties of the reservoirs. Traps and high-quality reservoirs within the regional traps are beneficial for the gas accumulation.
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