Abstract: The analysis of tested pressure and the study of abnormal pressure characteristic in partial prospecting wells indicate that there exist various types of pressures in southwestern Qaidam basin and abnormal overpressure in certain depth. But different structural units have different characteristics in initial horizon, initial depth of abnormal pressure and their section features. According to oil-gas accumulation mechanism under abnormal pressure, the hydrocarbon accumulation phases are classified, and the effects of the abnormal overpressure on reservoir type and distribution are analyzed. The study shows that the mud fracture in overpressure zone and lithologic reservoir should be the target domains for petroleum exploration.

Key words: Qaidam basin, abnormal pressure, reservoir, effect