A Novel Approach for Quantitative Study on Two-source-mixed Natural Gas Reservoirs

CHENG Fu-qi; JIN Qiang

Calculating ratio of source-mixed natural gas is important in study ing source-mixed gas reservoir. For a two-source-mixed gas reservoir, the follow ing w orkmust be done: (1) analyzing the geological factors of formation of source-mixed gas reservoir, confirm ing potential source rocks, (2) based on experimental data of ascertained source rocks andmeasured data of natural gas, f ind ing geochemical modes of different end-gas and source-mixed gas, then using themodes to calculate ratios of source-mixed gas andmaturity of source rocks, (3) using the ratios to analyze the format ion process of source-mixed gas reservoir, proposing geochemical trappingmechanism. The natural gas in Ordovician weathering crust reservoir in the Central Portion Gas Field in Ordos basin is source-m ixed gas of Upper Paleozoic coal-typed gas with Lower Paleozoic oil-typed gas. Starting w ith analyzing geoloical factors and process of the source-mixed reservoir, with geochemical parameters of percentages and carbon isotope composit ions of methane and ethane, a calculating model of rat ios w as established and a calcu lating graph of ratios was given in this paper. 13 gas samples collected from Jianbian gas field were analyzed using the method. The percentages of Upper Paleozo ic coal-typed gas and Lower Paleozoic oil-typed gas are 22~ 84 percent and 16~ 78 percen,t respective ly, according to 11 samples ( samples collected from Well Shan21 and Shan5 were excluded). Based on the result, we could draw a conclusion that Lower Paleozoic oil-typed gas, with the percentage of 63.2, is dom inant in Ordovician weathering crust reservoir in the Centra lPotion gas field in Ordos basin

College of Geo-resources and Information of University of Petroleum, Dongying, Shandong 257061

Received Date: 2004-10-18

Rev Recd Date: 2004-12-24

Publish Date: 2005-09-10

Key words:

Abstract: Calculating ratio of source-mixed natural gas is important in study ing source-mixed gas reservoir. For a two-source-mixed gas reservoir, the follow ing w orkmust be done: (1) analyzing the geological factors of formation of source-mixed gas reservoir, confirm ing potential source rocks, (2) based on experimental data of ascertained source rocks andmeasured data of natural gas, f ind ing geochemical modes of different end-gas and source-mixed gas, then using themodes to calculate ratios of source-mixed gas andmaturity of source rocks, (3) using the ratios to analyze the format ion process of source-mixed gas reservoir, proposing geochemical trappingmechanism. The natural gas in Ordovician weathering crust reservoir in the Central Portion Gas Field in Ordos basin is source-m ixed gas of Upper Paleozoic coal-typed gas with Lower Paleozoic oil-typed gas. Starting w ith analyzing geoloical factors and process of the source-mixed reservoir, with geochemical parameters of percentages and carbon isotope composit ions of methane and ethane, a calculating model of rat ios w as established and a calcu lating graph of ratios was given in this paper. 13 gas samples collected from Jianbian gas field were analyzed using the method. The percentages of Upper Paleozo ic coal-typed gas and Lower Paleozoic oil-typed gas are 22~ 84 percent and 16~ 78 percen,t respective ly, according to 11 samples ( samples collected from Well Shan21 and Shan5 were excluded). Based on the result, we could draw a conclusion that Lower Paleozoic oil-typed gas, with the percentage of 63.2, is dom inant in Ordovician weathering crust reservoir in the Centra lPotion gas field in Ordos basin

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A Novel Approach for Quantitative Study on Two-source-mixed Natural Gas Reservoirs

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