Hydrocarban preservation conditions and preferential exploration targets in marine sequences of nanpanjiang depression

Abstract：The hydrocarbon preservation conditions are the key factor for making oilgas exploration decision in marine sequences of Southern China. The basic characteristics of the preservation conditions in Nanpanjiang depression were investigated. Based the analysis of the re sponse characteristics of fluid chemical-dynamical behaviors in fault zones, sealing of mudstone cap rock, damage of denudation, present underground hydrodynamic characteristics and opening degree of hydrogeology, the high risk region was excluded, and the relative favorable ex ploration blocks were selected, eventhough the regional geological background was disadvan-raged. The results show th high, the infiltration depth for petroleum preservation. at the opening degree of Nanpanjiang and Youjiang fault zones are of present meteoric water is large, which offers a poor environment e middle-temperature hot springs of Balin structure in Nanpan jiang depression offer a poor environment for the Yangba block covered with residual mudstone and preservation of natural gas as well. In the silty mudstone of Middle Triassic, faulting-fracturing is weak, oilgas may be preserved. These regions are relatively favOrable exploration blocks. The Nanpanjiang depression was uplifted and denudated during the period of late Trias- sic Indosinian movement and Yanshan-Himalayan movement after Cretaceous respectively. The oil and gas reservoirs formed in Indosinian were damaged by Indosinian movement, but that damage is relatively weak. The sedimentary cover undergone strong squeezing, uplifting and denudation because of the Yanshan-Himalayan movement, which cause serious damage to the hydrocarbon preservation of Nanpanjiang depression. Of which, the most affected areas is the Permian or the strata below outcrop surface. The Permian, Carboniferous and Devonian For- mation are covered with Triassic strata and still of hydrocarbon potential.