Study On Structure Character And Its Relation With Petroleum-gas Of Shiwanshan Basin In Guangxi Province

Shiwanshan basin has a Mesozoic to Cenozoic continental sedimentary cover lies over a basement of marine-facies Indosinian deformation.Based on abundant field materials data and directed by the idea of mobiles and stage, regional structure,main fault , structural styles , tectonic stress field , structural unit and tectonic evolution were researched.The methods,including apatite fission-track method which was applied as main means,fliud inclusion and vitrinite reflectance method,were used to qualitatively and semi-quantitatively study the thermal evolution of the basin.Regional faults often show contemporaneous normal fault system related with extension in late Paleozoic era,and they experienced multiperiodic tectonic reversal or tectonic deformation with strike slip after Indosinian.Structural styles in the basin can be divided into four types.The basin can be plotted into three order structural units,and the tectonic evolution of the basin can be divided into five stages.The thermal and denudation history in the basin reflected its structural evolution.The hydrocarbon maturity history was under the control of the thermal evolution.At least six stages of the paleo-thermal evolution in the basin were identified:fast-buried increasing-temperature(T3-J3),temporarily decreasing-temperature(Late of J3-Early of K1),buried increasing-temperature(K),fast decreasing-temperature(Late of K2-E1),slightly varying-temperature(E2-E3)and another fast decreasing-temperature(N1 to present).The study showed that the best hydrocarban-bearing formation was the upper Permian in the basin,and Shilang-Shangshi belt was a good prospect area.