THEORY ANALYSIS ON DEEP SEATED GAS AND ITS POTENTIAL STUDY

In recent years, the concept of deep seated gas was commonly mixed up with deep gas in some published articles. In sedimentary, it is better to make the main oil and gas generating zone (oil generating window) as the limit of hydrocarbon generating depth, and the gas that seated in the strata between the depth and sedimentary basement should be named deep seated gas. But to the earth, it is better to name the gas that seated in and under sedimentary crystalline basement as deep gas. Of course, the gas that generated in deeper strata but reserved in shallower strata should also be a important kind of deep seated gas. The generation of deep seated gas relate to the vertical zonation of hydrocarbon generation in earth crust. The theory of oil and gas generating zonation for sedimentary basin have effect on exploration practice in some historical period or in some basins. But with the development of oil and gas geology theory study and exploration practice, the limit of threshold indicate that was made for oil phase disappearing and gas phase appearing in the theory of oil and gas generating zonation was find by scientists. Different basin has different depth for main oil generating zone, so for main gas generating zone (dry gas zone). The sapropeltype organic matter evolution need higher temperature and biger depth and its main gas generating zone is deeper than humictype organic matter's. Evolution of organic matter in main gas generating zone is controlled by many different factors, including some important factors, such as temperature, depth and time. The causes that lead temperature higher are earth dynamics, heat flux in earth deep, and so on. The important geological events taken place before Paleozoic have prepared abundant organic matter and evolution condition for deep seated gas generating. So taken from matter base, there have a great resource potential for deep seated gas. Earth dynamics for oil and gas generating and other new idea offer a new way for deep seated gas study. The resources of hydrocarbon in lithosphere are not used up, but also all resources that have been proved and mined are only a small part of the whole. The main of hydrocarbon resources may be explored in the deep.