Research On Genetic Types And Formation Conditions Of Shallow Gas In Northern Songliao Basin

The problems of genetic types, forming condition and perspective and target areas of shallow gas in Songliao Basin are demanding prompt solution currently. This project with an eye toward cutting-edge natural gas analysis study technology at home and abroad, commenced from the geochemical characteristics of the shallow gas, analyzed of the physical properties characteristics of mudstones, the geochemical characteristics of crude oil, the characteristics of formation wate and so on. Combined with the relationship of the distribution of oil-gas-water and the geological condition of structure, fault ages and so on, the project strived to make experimental technique and research approach breakthrough. Finally the establishment of gas compinent segmentation cutting detection and light hydrocarbon carbon isotope analysis technology, and provided technical support for the following shallow gas exploration deployment. Major achievements are as follows:1. The shallow gases we have discovered in Songliao Basin are mainly secondary gas, including oil associated gas(Lamadian,Xingshugang,Xinzhan,Sizhan and Chaoyanggou area), oil degradation gas(Punan,Aonan and western slope) and high-postmature gas(Songzhan,Shengping,Changchunling and so on). At present, the biogas from source rocks in Songliao Basin is only gas display.2. The oil associated gas is from oil in the underlying oil layer which go through vaporization and gas-washing, and with the link of fractures accumulated in the shallow.The formation of this kind of gas reservoir needs underlying oil reservoir, fractures which link the oil reservoir to shallow formation and weak late tectonic movement. The relatively favorable areas of oil associated gas are Longnan oilfield and Gulong oilfield in Gulong depression, Yingtai area and Longhupao terrace, becides North Changyuan,Xinzhan,Baiyinnuole,Sizhan and Chaoyanggou where have already found oil associated gas.3. The formation of oil degradation gas needs the active formation water which can provide enough nutrition to keep microbe surviving; the formation water is connected with the surface water by reservoirs and faults; accumulation late and weak terminal tectonic activity. Apart from the Saertu oil layer in western slope and Heidimiao oil layer in Changyuan where have already found, the relatively favorable areas of oil degradation gas are Aogula oil-gas field, Longhupao oilfield, the Saertu oil layer in Puxi oilfield and the Heidimiao oil layer in Longnan and Gulong oilfield.4. The biogas from source rocks needs low mature source rocks, enough organic matter and relatively higher source rocks permeability to fit microbe to survive.and the terminal tectogenesis had better weak. Currently the permeabilities of mudstones which depth deeper than 500 m in Songliao Basin are mostly lower than 0.1 m D. Have already not suitable for generating biogas yet. The early biogas probably has to seek in the weak tectonic activity areas. The Binbei area, especially Wuyuer depression, Fuyu structure and Longhupao depression are favorable areas, which have lesser faults distribution and weaker terminal tectonic activity.5. The high-postmature gas needs underlie deep gas supply, needs connect with faults and less terminal tectonic destructions. High-postmature gas is in close relations to the source rocks distribution of Shahezi Group and mainly distributes in the area where Shahezi Group source rocks are thicker.