1.School of Engineering and Technology,China University of Geosciences(Beijing),Beijing 100083, China 2.No.4 Gold Geological Party of CAPF,Liaoyang 111000,China 3.Guangzhou Marine Geological Survey,Guangzhou 510075,China 4.Hunan Geo-sun High Technology Limited Company,Changsha 410208,China 5.HunanHuasheng Energy Resource and Investment Development Co. Ltd.,Changsha 410004,China
Dongting Lake Basin has the conditions for forming biogenic gas reservoirs of certain scales. For the exploration of biogenic gas resources, the authors carried out a comprehensive exploration work mainly based on geochemical methods during the period of 2013~2016, and conducted fairly systematic surface sediments survey. Geochemical exploration covered an area of 2060 km2, and collected 1498 samples. All the samples were tested by in situ headspace gas (free hydrocarbon), indoor acidolysis hydrocarbon and a small quantity of methane isotope indexes. The results are as follows: 1. The geochemical anomaly of methane in the Dongting Lake basin is composed of free hydrocarbon (headspace gas) and adsorbed hydrocarbon (acid hydrolysis hydrocarbon). The free hydrocarbon is a dynamic reflection of the existing underground biogenic gas, and the hydrocarbon accumulation of the acidolysis hydrocarbon is related to the distribution of the paleo-channel. 2. The Dongting Lake basin is the area of a high background and high anomaly of methane, and the distribution of the abnormal area is basically consistent with the distribution of the Quaternary fault basin, especially in Yuanjiang sag. 3. Acidolysis hydrocarbon anomaly of the Heba Town, bead-like anomaly in NE direction and southeastern secondary local anomalies form a ring anomaly zone surrounding the Yuanjiang sag, which means that the sag may be the potential supply area of biogenic gas in Dongting Lake basin. 4. The area of Qingshuzuie-Heba Town north of Yuanjiang sag is the abnormal high value area of the hydrocarbon methane in Dongting Lake Basin, and this is the direct reflection of natural gas seepage in shallow surface. The high value of acidolysis hydrocarbon methane surrounds the anomaly area of free hydrocarbon methane in Qingshuzui, which constitutes the best combinational hydrocarbon reservoir model. The area of Qingshui-Haba Town is the 'chimney' of the biogenic gas underlying the Dongting Lake Basin and hence the most hopeful breakthrough area for biogas survey in the Dongting Lake Basin.
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