| Based on the development characteristics of Carboniferous Huanglong terrigenous clastic deposits and the development locations of gravels with some psephicity, two transgression channels can be deduced to be present on the southeast of Yunyang and the northwest of Dazhou, and two tidal-flat depositional systems form along Chongqing-Wanzhou and to the southeast of Dazhou in the east of Sichuan Basin, where a suit of relatively complete Type–I sequence that is composed of LST (C2hl1), TST (C2hl2) and HST (C2hl3) developed. Different sedimentary microfacies of
the Huanglong tidal-flat systems control the vertical distribution characteristics of the reservoirs, in which the grainy shoal facies is of the best reservoir properties. Through the qualitative analysis to the erosion degree of the Huanglong Formation during epidiagenetic karstification stage by using trace elements, carbon and oxygen isotope data, it is suggested that the Huanglong Formation did not suffer intensive weathering and its residual thickness is representative of the primary thickness in character. Hence, the tidal channels can be mapped by the residual thickness of the Huanglong Formation. Depending on the prediction of drilling and seismic data to tidal channels, it is indicated that the features of tidal channels have obvious control of the spacial distribution of high quality reservoirs. |
