摘要
an id="EnChDivSummary" name="EnDivSummary">A set of dark shale deposits was found in the Lower Silurian Longmaxi Formation in the Sichuan Basin and was considered as potential shale gas reservoirs.According to the theory of sequence stratigraphy,natural gamma ray and sonic logging data were integrated with seismic data to perform the sequence stratigraphic study and to map the favorable shale gas reservoirs.The Longmaxi Fm can be divided into 5 seismic sequences and 22 logging sequences.The logging sequences were correlated with the seismic sequences on synthetic profiles and inter-well logging sequence correlation was performed with the seismic sequence framework as constraint.A three-layer sequence model was thus built in this study area,consisting of 2 low frequency super-sequences,5 medium frequency seismic sequences and 22 high frequency logging sequences.Additionally,a sequence stratigraphic model of the shale gas reservoirs there was also established through a comprehensive analysis of each well’s gamma ray curve.The gamma ray curves show two geometries,i.e.an ascending one and a descending one,which were interpreted as transgressive system tract and retrogressive system tract respectively.The quality gas shale mainly occurs in the condensed succession near the maximum flooding surface.It is believed that the favorable shale gas reservoirs are mainly distributed at the bottom of Longmaxi Fm and correspond to the middle-lower interval of super-sequence 1 or seismic sequence 1 and logging sequences 2-5.These understandings can be used to guide the exploration of shale gas in the Longmaxi Fm of the Sichuan Basin and mapping of shale gas reservoirs also in other regions.an>
