The clastic reservoir rocks from the Kalashayi Formation on the Akkol uplift of the Tarim Basin,Xinjiang

The clastic reservoir rocks from the Carboniferous Kalashayi Formation on the Akkol uplift of the Tarim Basin,Xinjiang consist mostly of lithic arkosite,and the feldspar contents are found to be higher than those of lithoclastics.The clastic reservoir rocks exhibit low compositional maturity and textural maturity,point to linear contact between grains and pore-space cementation by carbonate rocks.Although the early carbonate cementation may cause the decrease of the primary porosity and permeability of sandstones,it has contributed to the formation of secondary porosity.The amounts of secondary porosity are much more than those of the primary porosity.It can be seen from the data obtained from mercury-injection method that the pore throats display an inhomogeneous distribution,and both the porosity and permeability are relatively low,indicating the moderate or low porosity and low permeability of the reservoir rocks.The diagenesis in the Kalashayi Formation may be assigned to Stage A of late diagenesis.Abundant secondary pore spaces created by the dissolution of early calcite are considered as the important oil-bearing structures in the study area.