Northeast Sichuan Feixianguan oolitic beach distribution
|School||Southwest Petroleum University|
|Course||Mineral prospecting and exploration|
|Keywords||Northeastern Sichuan area Feixianguan Formation platform margin bank inter-platform bank basement rift|
The indistinct knowledge of oolitic-shoal distribution in Feixianguan Formation, Sichuan basin, had limited the successful ratio of exploration and development on the gas pool.Feixianguan Formation can be divided into four members:Fei1(T1f1), Fei2(T1f2), Fei3(T1f3) and Fei4(T1f4). The intended interval of research region has deposited integrity, as well as distinct boundary between each member which can be well horizontally traced and contrasted. The thickness of Feixianguan Formation, in platform margin, has increased visibly from East area to West especially in Fei1and Fei2member, whereas it is steady in inter-platform. Grain carbonate rocks mainly develop in Fei1, Fei2and the middle-bottom of Fei3, which present a signature identity in the strata section. Feixianguan Formation is entirely identified as carbonate platform environment and includes several kinds of subfacies: demi-restricted—evaporate platform, platform margin, slope and ocean trough, been constituted with various typess of micro-facies,just like platform margin bank, inter-platform bank, demi-restricted lagoon, evaporate lagoon, tidal flat and others.Lithology of oolitic-shoal are mainly thick bed massiveness light gray-taupe oolitic dolomite and limestone. On log response, the GR curve of the bank core in platform margin oolitic-shoal tends to pose a box-shape of the flat-low amplitude, and appear as crenulate-box or finger shape alternately assemble with high amplitude area in the shoal margin or inter-platform bank. Oolitic-shoales preferentially develop on the underwater landforms highland and have arbitrary thickness, with the influence of high frequency sea level change and finally form the hundred meters buildup of oolitic-shoale in the carbonate platform margin.The sedimentary facies belt nearly extends from northwest to southeast of the research region in Feil and Fei2period, and the platform margin,being shaped as narrow belt and bending boundary, is characterized with the platform margin bank which deposited along the platform margin intermittently. When it comes to Fei3period,the landform of deposit basement get more smooth develops to a homogenous carbonate platform, and the inter-platform bank has the same distribution which controlled by the early depositional physiognomy as in Feil and Fei2period.Two series of positive basement rifts, in directions of NE and NW in early Triassic, dominate the differentiation of sedimentary framework: syndepositional tension of basement cracking in NW manages the distribution of platform margin; syndepositional positive fault, in NE direction, aggravates the differentiation of sedimentary landform in platform margin. The two series of basement rift form the distribution model, presenting as sedimentary belts" dominated by NW, Decorated by NE". The sea level change no only dominates the thickness of single oolitic-shoal and the gross thickness of platform margin bank, but also impacts the priority zone, the lateral migration of oolitic-shoal, and the expanding of deposition range. The two elements, sea level change and basement rift, dominate the distribution of oolitic-shoal in Feixianguan Formation, Northeast Sichuan Basin.