| Abnormal overpressure is popular in the northwestern Qaidam Basin,and the study on the spatial distribution and formation mechanism of overpressure is the key to evaluate the hydrocarbon accumulation conditions and resource potential.Based on the measured pressure and the pressure data which calculated by the equivalent depth method,the horizontal and areal distribution characteristics of abnormal high pressure in the area are analyzed.Combining the time-difference curve of acoustic wave of mudstone,deposition rate,lithologic characteristics,hydrocarbon generation potential of organic matter and tectonic compression,the genetic mechanism of overpressure was analyzed and quantitatively evaluated.Through analyzing the feature of stratigraphic pressure and oil and gas distribution in Nanyishan.The thesis discussed the influencing factors of formation overpressure.The results show that the initial depth of overpressure in the area is about 1500 m,which is mainly developed in the Laohehe Formation of Miocene to upper Ganchaigou Formation of the Miocene,and the formation pressure is increasing with the depth.Undercompaction,organic matter generation and tectonic compression are important factors for overpressure formation and evolution.The results show that undercompaction is the most important controlling factor,and its contribution rate is up to 60%;secondly,the contribution of tectonic compression is about 20-30%;The contribution of organic matter generation is the least.The salinity characteristics of the northwestern Qaidam Basin show that the formation of the overpressure is also affected by the salinity of the pore fluid and the salt-bearing plastic layer deposited in the salt-brackish water environment.There is a low-pressure compartment in the Xiayoushashan-Shizigou Formation,where Low pressure oil pool is exisited;there is a overpressure compartment in the Lulehe-Shangganchaigou Formation,where condensate gas reservoirs and tight sandstone gas pools are exisited. |
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