PETROPHYSICS AND EVALUATION OF THE KALASHAYI FORMATION, TAHE OILFIELD

Although the Carboniferous Kalashayi sandstone reservoirs of Tahe Oilfield in Tarim Basin are buried at the depth of 4 800-5 200 m,they have fairly good petrophysical property.The porosities range generally from 8% to 12%,with the maximum of 20%;and the permeabilities vary typically from 10×10^-3 to 100×10^-3μm²,with the maximum of over 1 000×10^-3μm².Mercury injection data indicate that,the reservoir is characterized by medium-pore-coarse-throat structure with coarse skew in pore size distribution.Thin sections with blue epoxy impregnation and electron microscope scanning photograph show that' the main pore types are intergranular and intragranular pores from dissolved feldspar and residual original intergranular pores,while the smaller part of porosity is contributed by interstitial microcrystalline to very fine crystalline limestone intercrystalline pores and fissure pores.It is obvious that the depositional facies and distance from the source area affect porosity and permeability which increase conspicuously approaching to source area along with the enhancement in quantity and thickness of channel sandstones.The present reservoir prediction is still mainly relied on sand bodies forecast by means of analysis of seismic data and depositional facies due to the lack of method for spatially predicting the dissolution of feldspars.