Feldspar dissolution and its effect on reservoir in Kepingtage Formation, Shuntuoguole Low Uplift, central Tarim Basin

Thin section data showed that primary intergranular poreswere dominant in the tight sandstone reservoirs in the Silurian Kepingtage Formation in the Shuntuoguole Low Uplift of the Tarim Basin, while secondary pores formed by feldspar dissolution took the second place. The feldspar dissolution characteristics, mechanism and its effect on reservoir physical property were analyzed using thin sections, scanning electron microscopy (SEM), energy spectrum and X-ray diffraction (XRD). The proportion of secondary porosity formed by potassium feldspar dissolution was much larger than that from plagioclase, and albite was almost not dissolved. From the early Devonian to the late Jurassic, potassium feldspar dissolution resulted in the formation of secondary porosity, and the secondary pores only developed in the area not covered by asphalt. Dissolution products were mainly illite and the mixture of illite/smectite, although they could hinder secondary quartz overgrowth to some extent, greatly reduce connectivity among the pore throats of the sand body reservoir, and greatly influence the reservoir permeability.