Evaluation Of Biogas Resources In Baoshan Basin, Yunnan

Baoshan gas field is a typical small gas field with water by nonmarine organic matter biodegradated in unconsolidated sandstone shallow layer in upper Tertiary.By the May,2005, the explorations have resulted in 438km of 2-D seismic data and drlling 14 wells with total footage of 11008m and 9 wells have attended commercial gas, the drilling efficiency is 67%;8 wells located in YongZhu street, s anticline,only lwell located in XiaoGuanMiao corner structure.With the continuously advance of the explorations, the explorations become increasingly difficult,which restrict the explorations of BaoShan gas field.On the basis of predecessor, s research, auther study the evalution of biogas resources in BaoShan.The Yanghu formation and Nanlin formation source rock of Baoshan basin is mainly argillaceous rock with high organic abundance, the organic abundance in number 2—number 5 of Yanghu formation and number 1 of Nanlin formation is more than 1% on average and is considered as the middle or good source rocks, especially the number 4 of Yanghu formation is considered as the most important gas source rock in Yanghu formation, and its organic abundance is 1.59% on average. The organic abundance in Number 1 of Nanlin formation is equally abundant, it is 1.82% on average, it can be considered as gas source rock of biogas in its prematurity phase. The curve of saturated hydrocarbon apparently appears double peak, the dominant peaks are nC27 and nC29,and the nC29 is main; it is considered as the inputed organic matter mainly is terrestrial organic matter. The ratio of pristane and phytane is on the range of 0.518-1.881, showing the sedimentary environment is weak oxidation or weak reduction. The degree of organic metamorphism(Ro) of Yangyi Formation is between 0.31% and 0.45%.The pyrogenic Tmax is usually below 434℃,mainly between 410℃and 420℃. The saturated hydrocarbon of dissoluble organic matter is odd/even predominant apparently. The organic matter is being the condition of immaturity, and it is the alert phase of methane-bacteria.Currently, there is still a bulk of biogas being generated.Multidisciplinary analysis gas Geochemical data,the gas from Yangyi Formation in BaoShan basin is dry gas that mainly contain methane and a little inorganic gas, isotope of methane is between -59.03‰to -63.35‰, this is a typical biogas and low contamination and high thermal value, hydrogen isotope(δD) of methane from BaoShan basin is between -254‰to -260‰, this isotope ratio is low light, it is manifest that gas is generated by nonmarine organic matter biodegradated.According to estimated value by hydrocarbon expulsion coefficient method and exploratory stratigraphy method (GOGS), The total amount of biogas generated from upper tertiary in BaoShan basin is 17-19 BCM.Now, 50%of the natural gas resources are found out, but because of little trap area, potential resources might main distribute in nonstructural trap, it is difficult to further explore resources.