The hydrogeological and hydrogeochemical characteristics of ground water are closely related to hydrocarbon migration

accumulation

and preservation conditions.Ground water can be vertically divided into three zones:free exchanging zone

exchanging-retarded zone

and exchanging-stagnant zone.The exchanging-retarded zone is favorable to petroleum preservation because it is not influenced by surface water

while the free exchanging zone

strongly affected by long-time erosion and oxidation of surface water

offers a poor environment for petroleum preservation.Reconstructed by several tectonic activities

the preservation conditions for oil and gas reservoirs of marine strata in southern China is severely disturbed.Through analysis of the hydrogeological and hydrogeochemical characteristics and their relation with hydrocarbon preservation conditions in several exploration areas of southern China

the concept of preserved meteoric water is put forward and the formation of preserved meteoric water and its geochemical characteristics are discussed.The preserved meteoric water occurring near unconformities can be used as an indicator of poor preservation conditions.Based on the concept

a relatively systematic hydrogeochemical index system for distinguishing hydrocarbon preservation conditions is established for the marine strata in southern China.