Abstract:

According to the production characteristics of the abnormal high temperature gas reservoir,the producing me-chanism of condensate water in gas wells,and the salinity characteristics of the produced water in the Qianmiqiao buried hill,we believe that the gas reservoir of the Upper Paleozoic was formed during the abnormal high temperature phase in Ordos Basin.The abnormal high temperature resulted in not only the generation of methane but also the vaporization of some formation water and the formation of abnormal high pressure.The gas (vapor) diffused upward under the driving of the abnormal high pressure.This gas migration led to the decreasing of pressure in the lower strata and the speeding up of formation water vaporization.The vaporization of formation water may in turn increase the pressure of the lower strata,leading to a new round of hydrocarbon migration.This process may repeat again and again,gradually making the me-thane,the vapor,the associated temperature and pressure diffuse to the whole compartment,realizing local balance of potential field in the compartment,and finally resulting in the formation of gas reservoirs of high temperature and pressure in the basin.After that,uplifting and erosion cause the lowering of temperature and pressure,while liquefaction of vapor leads to the decreasing of vapor density,methane concentration and gas column pressure,resulting in the formation of underpressured gas reservoirs.

Key words: phase state, compartment, underpressured gas reservoir, formation water, Upper Paleozoic, Ordos Basin