Systematic  Analysis of Geotemperature Influencing on Migration and Accumulation of OilGas Fluids

Key words: 
• geotemperature /
• influence

Abstract: As poolforming energy parameters, geotemperature and pressure influence the whole process from oilgas generating, migrating and accumulating  to dissipating. The controlling mechanisms of geotemperature on oilgas generated and geopressure on migrating have been investigated, while influences of geotemperature on oilgas migrating and accumulating have not been considered sufficiently. In order to uncover geotemperature influence on migrating and accumulating of oil and gas, physical, chemical and physical chemical mechanisms during oilgas migrating and accumulating have been investigated systemically. After these investigating and analyzing, a conclusion that each reservoiring processes of oil and gas are influenced by geotemperature has been gained.
 There are two types of influencing mechanisms of geotemperature on oilgas migrating. Proving dynamic and driving oil and gas directly is the first mechanism. Inhomogeneous distribution of geotemperature could provide heatstress which drives oil and gas migrating directly. According to the heat stress theory, if temperature differences exist among different parties of a same body, heat stress would appear immediately. As giant geological bodies, stratums not for a moment have homogeneous temperature. Those eternal temperature differences imply timeless heat stress which has been and will be driving oil and gas migrating from higher temperature area to lower temperature area. The inference that temperature could drive oil and gas has been testified by Qiu Nansheng's experiment, in which the phenomenon of oil migrating from the higher temperature end of tube to the lower end was observed.
 In oilgas migrating process, geoheat could not only provide power for oilgas migrating, but also control migrating efficiency by changing some physical parameters, such as sorption, diffusivity and solubility. According to present relative achievements about accumulation of oil and gas, geotemperature not only partly influences accumulating location of oil and gas, but also mainly controls oil and gas's accumulating phases. Where oil and gas will accumulate in is determined by many factors, such as source rock, reservoir, capping, migrating process, preserved process, etc. However, these factors are more or less influenced by geotemperature. Based on phase of reservoired oil and gas, reservoirs could be classified into heavy oil reservoir, normal oil reservoir，condense oil reservoir，oilgas reservoir and gas reservoir. Phase of reservoired oil and gas is determined by their primordial phase and subsequent change. Geotemperature is one of the two primary factors that determine primordial phase of oil and gas (another factor is the organic materials type of source rock). According to present data gain from experiments and experiences, reflection of vitrinite(Ro %), the directly decisive parameter of primordial phase of oil and gas, is a function of geotemperature. In Zhanhua sag, when geotemperature is under 100℃ (Ro<0.5%), the source rock in Es3x generates biogas only. From 100℃ to 175℃(Ro is from 0.5% to 1.35%), routine oil is the main produce. When geotemperature increase to 175℃(Ro>1.35%), produce of the source rock is condensable oil containing with wet gas. When geotemperature is above 200℃(Ro>2.0%), produce of the source rock will be dry gas only.
 In summary, in accumulating, distributing situation and accumulating phase of oil and gas are influenced by geotemperature (associating with pressure). Two facts are noteworthy, the first one is that geotemperature is not only, but one of many factors which control reservoiring processes of oil and gas. According to the authors, geotemperature has inherent relationships with geopressure and tectonic stress, and the three factors always control oil and gas migrating and accumulating cooperatively. Another one is that the oil and gas reservoirs we are looking for all reservoired during geological time. It is the paleogeotemperature that influenced oil and gas's migrating and accumulating process. So paleogeotemperature should be estimated before analyzing influences of geotemperature on oilgas migrating and accumulating.