Preliminary Study on Genetic Types of Natural Gas in Shiwu Fault Depression

This paper discussed the genetic types of natural gases in Shiwu fault depression based on the analyses of gas component composition,light hydrocarbon parameters and carbon isotopic compositions.The result indicates that the natural gases in Shiwu fault depression can be divided into two categories:Associated gas and independent reservoir gas,furthermore,the gases can subdivided into four types according to organic matter origin and thermal evolution stages.Most of the natural gas in Qinjiatun,Taipingzhuang and Qikeshu areas is associated gas,belonging to partial sapropelic pyrolysis gas based on light hydrocarbon parameters and carbon isotopic compositions which can reflect the organic types and thermal evolution degrees.The natural gas in Pijia,Bawu,Shiwu and Siwujiazi areas is independent reservoir gas,belonging to transitional cracking gas.The natural gas in Gujiazi is independent reservoir gas,and belongs to high maturity humic mixed gas judged by the completely reversal carbon distribution series indicating inorganic gas mixed.The natural gas in Houwujiahu also belongs to independent reservoir gas and the carbon distribution series show completely reversal or partly reversal,indicating inorganic gas mixed,thus belonging to high maturity transitional mixed gas.