RESEARCH ON SEDIMENTARY FACIES AND RESERVOIR CHARACTERISTICS OF LOWER CRETACEOUS IN EASTERN WUSHI SAG, TARIM BASIN

The Lower Cretaceous mainly develops in eastern Wushi Sag of the Tarim Basin,which is a series of redish brown sandy conglomerate deposit,featuring coarse grain size and poor roundness and poor sorting.Fan delta and lake facies are the dominant types of sedimentary facies of Lower Cretaceous in eastern Wushi Sag.Debris flow deposits are common in fan delta plain subfacies,and submerged distributary channels largely develop in fan delta front.The lake was extensive and shallow,and grew shore-shallow lacustrine muddy banks and sand bars,the later interlayered in the former as thin layers.Fan delta front sand body and shore-shallow sand bar are favorable hydrocarbon accumulating bodies.The reservoir is middle-fine lithic sandstone and features low porosity and low permeability,developing in middle Shushanhe Formation.Dissolved pores between grains and dissolved pores in grains are the main storage and accumulation space.The controlling factors of effective reservoir were analysized: sedimentary process and interstitial material are important,and diagenesis especially corrosion is also decisive.The distribution of favorable sand bodies in 3-D seismic work area was predicted by the research on wave impedance inversion,which would direct the reservoir distribution forecast.