Relationship between Tectonic Evolution and Hydrocarbon Accumulation in the Changxing and Feixianguan Formations in the Frontal Concealed Structural Zone Of Micangshan Mountain, Northeastern Sichuan Basin
摘要
The frontal concealed structural zone of the Micangshan Mountain,northeastern Sichuan Basin,is a prospective area for oil and gas exploration,but the exploration degree there is still low due to the intensity of tectonic deformation and the complexity of hydrocarbon accumulation process.Beginning with the relationship between tectonic evolution and hydrocarbon accumulation,we discussed the correlations between hydrocarbon accumulation in the Permian Changxing Fm and the Lower Triassic Feixianguan Fm and the Emei taphrogeny and the formation & evolution of the Micangshan Mountain respectively.The Emei taphrogeny controlled the formation of Kaijiang-Liangping shelf,which provided the source rocks and reservoir spaces for hydrocarbon accumulation in the Changxing and Feixianguan Fms.On the other hand,low temperature geochronological data revealed that large-scale uplifting of the Micangshan Mountain occurred in the Late Yanshan and Himalayan epochs.In the Late Yanshan epoch,the Micangshan Mountain began to strongly uplift,the basement fault decoupled,and the folds experienced flexural deformation of southwards progressive type.In the Himalayan epoch,it uplifted again and compressed southwards,leading to the passing of stress further southwards and deformation of folds in the structural low.The formation of the Micangshan Mountain has strong control on the process of hydrocarbon accumulation in its periphery,which is divided into 3 stages,namely fossil oil reservoir formation(Late Indosinian-Early Yanshan),fossil gas reservoir formation(Mid-Yanshan),and deformation of oil/gas reservoirs(Late Yanshan-Himalayan).Finally,it is pointed out that current large-scale gas reservoirs are mainly distributed in reef-shoal reservoir strata in the epiplatform of the decollement fold belt.