Abstract:

Guided by the high-resolution sequence stratigraphy theories and methods,the authors divided the Upper Triassic Xujiahe Formation into 4 long-term sequences and 14 medium-term sequences through sedimentary dynamics analysis of the structures of base level cycle and superimposition patterns and combining comprehensive study of outcrops,coring,logging and seismic data.A sequence stratigraphy framework of the long-term and medium-term cyclic sequences in Sichuan Basin and West Sichuan depression was also constructed under constrain of seismic reflection.Directed by the method of lithofacies paleogeographical mapping,they compiled lithofacies-paleogeographical maps for Sichuan Basin and West Sichuan depression with the elevating and falling fa-cies tracts of long-term and middle-term base level cycle as the mapping units,established high-resolution stratigraphic framework with short-term cycle as unit in 3D seismic survey area.Taking the sequence interface and lake flooding interface of long-term and middle-term cycle as the unit,they also set up low-frequency model and then used it to perform seismic lothological inversion and map sandbodies thickness and sedimentary microfacies of short-term cyclic sequences.Finally,they discussed the relationship between the sandstone distribution and base-level cycle variation and lacustrine ingression and regression,and predicted the vertical and horizontal distributions of potential sand reservoirs.

Key words: high-resolution sequence stratigraphy, GR pseudo-acoustic inversion, lithofacies paleogeography, prediction of sandstone distribution, Xujiahe Formation, West Sichuan Depression