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Shale gas preservation conditions for the Upper Paleozoic in Guizhong Depression
Pages: 534-541
Year: Issue:  4
Journal: Oil & Gas Geology

Keyword:  preservation condition for oil and gassealing capacity of cap rockstectonicsshale gasGuizhong Depression;
Abstract: The Middle and Lower Devonian as well as the Lower Carboniferous shale in the Upper Paleozoic in the Guizhong depression are favorable for hydrocarbon generation and accumulation ,but the preservation conditions of shale gas are very complex due to multistage tectonic activities .The shale gas preservation conditions in the Upper Paleozoic of the Guizhong depression were comprehensively evaluated and the play fairways were identified based on both macroscopic and microscopic analyses .Based on the field geological survey data , in combination with drilling data , vitrinite reflec-tance,clay mineral X-ray diffraction,physical property ,tectonic evolution history ,and reconstruction of burial history and thermal history ,we studied the shale gas preservation conditions in respects of the sealing capacity of cap rocks and the influence of faulting and uplifting .The following conclusions were obtained .The Middle Devonian shale in Guizhong de-pression has large thickness(of 250-650 m),continuous distribution,better ductility and high micro sealing capacity , thus can act as an regional cap rock for shale gas preservation .Although the Lower Carboniferous shale is limited in dis-tribution,it has good ductility and strong sealing capacity ,thus can act as local cap rocks .The Yanshanian period is the main deformation period in the study area ,during which large imbricated thrust faults and high angle thrust faults were developed and influenced the present distribution patterns of the shale gas reservoirs .The strong denudation in this area destroyed the preservation of shale gas .Tectonic activity was weak and the amount of denudation was small in the west-central part of the depression .In conclusion,the Tianshan anticline and its west area in Liujiang low salient ,the central part of Mashan uplifted as well as the central part of Hongdu shallow sag are the favorable areas for shale gas exploration thanks to their stable distribution and better ductility and strong sealing capacity as well as its weak tectonic destruction and weak denudation .
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