Squence Stratigraphic Characteristics & Its Control To Reservoir Of Jurassic In Malang Depression, Santanghu Basin

Santanghu Basin lies in the northeast of Xinjiang province; a congruent and reconstructed innertief which developed on the basis of rift-fault basin in Permian, its sediment cover is Permian-Quaternary Series. Malang Depression is a secondary structural belt of Santanghu Basin, Jurassic Series is the main oil and gas reservoir of the basin.This paper utilizes the basic theory and study methods of terrestrial-facies sequence stratigraphy, and divides Jurassic Series of Malang Depression into 3 third-order sequences and founds framework of sequence stratigraphy of Jurassic Series in Malang Depression combining seismic profiles, borehole log, and palaeontology and drill core data. Based on structural evolution, sequence constitution and developing characteristic of system tracts of main prototype basin in study area, it founds the pattern of sequence stratigraphy of Jurassic piedmont depression basin. Besides, it points out that dominant geologic factors such as tectonic movement, palaeoclimate and sediments supply control the forming and evolution of sequence stratigraphy of Jurassic Series in this area.According to facies marks such as drill cores, well logging, hole probe and palaeontology, it analyzes in detailed sedimentary facies and recognizes 5 sedimentary facies: alluvial fan, fluvial, lacustrine, fan-delta and braided stream delta, and 13 subfacies. In the framework of sequence stratigraphy, Lowstand System Tract mainly develops deposits of braided stream, offshore-meare, alluvial fan and prograded delta; Trangressive System Tract mainly develops lacustrine mudstone, and develops regressive depositional system; Highstand System Tract mainly develops depositional system of offshore-meare, fluvial facies and prograded delta.Sequences control development, distribution and evolution of sedimentary facies, and affect furtherly reservoir properties of reservoir strata. By studying on petrology, diagenesis, physical characteristics, porosity texture and heterogeneity, it is believed that this area develops 3 kinds of reservoir strata: medium porosity and medium permeability, medium porosity and low permeability, low porosity and low permeability. With the increase of buried depth, reservoir properties have a trend of becoming bad. Favorable reservoirs in SQ1 and SQ2 are all underwater distributary channel sand bodies of fan delta front and plain distributary channel sand bodies in Lowstand System Tract in the western area of Niuquanhu. In them, sand bodies in SQl Lowstand System Tract are IIA-type reservoirs in integrated assessment, while sand bodies in SQ2 Lowstand System Tract are better than SQl, they are IB-type and IIA-type reservoirs in integrated assessment. Favorable reservoirs in SQ3 are braided channel sandbars and underwater distributary channel sand bodies of braided delta front in Highstand System Tract in Niuquanhu and Mazhong, they are IIA-type in integrated assessment, and even can be IB-type in the western area of Niuquanhu.