CONTROLS OF THE CALEDONIAN PALEOUPLIFT TO THE SINIAN -LOWER PALAEOZOIC RESERVOIRING CONDITIONS IN JIANGHAN PLAIN

The study on the sedimentary filling and evolution in and around Jianghan Plain indicated that the Sinian-Lower Paleozoic source rocks and reservoirs in Jianghan Plain were controlled by the Caledonian paleouplift.The source rocks occured mostly in the deep depression area adjacent to the southern and northern flanks of the paleouplift,rather than in the paleouplift.Due to the paleouplift,the Sinian Doushantuo Formation was laterally significantly different in source rock from the Lower Cambrian Niutitang Formation.The source rocks in the depression area were evolved earlier than those in the slope belt and paleouplift.In general,the source rocks were developed earlier in the south and west than in the north and east.In the paleouplift,tide flat-lacustrine facies of restricted platform were dominant,favorable for development of dolomitic reservoirs.As a result of shallow waters and frequently changed eustatic sea level in and around the paleouplift,the dolomitic reservoirs were reworked with multi-phase karstifications during diagenesis,thus improving the reservoirs;such good reservoirs were typified by the Sinian Dengying Formation,Lower Cambrian Shilongdong Formation,and Upper Cambrian controlled by the Caledonian paleouplift.The Caledonian paleouplift was considered as a favorable destination for migration and accumulation of early liquid hydrocarbon,which was important for a petroleum exploration breakthrough of the Sinian-Lower Paleozoic reservoirs in Jianghan Plain.