Structural-mineralogical alterations of sandstones in rock-water and rock-water-oil systems within oil-water contact

Abstract

Structural-mineralogical alterations of sandstones under conditions of natural water-oil interaction within Jurassic sedimentary sequences in south-eastern Nurolsk sedimentary basin (Tomsk Oblast, Western Siberian, petroleum province) depend on their predominance in the fluid system and the dissolution-resedimentation process itself. Oil inflow and associated acid solutions into the reservoir resulted in rock-water disequilibrium: unstable minerals decompose and new stable mineral phases form. Under conditions of oil-filling reservoir, terrigenous reservoir alteration reveals zonal behavior. In the oil saturation zone (rock-water-oil system) solution and secondary mineralization are minimized; in the transition zone of water-oil contact (rock-water-oil and rock-water systems) dissolution is well-developed and accompanied by intensive kaolinitization; in edge water zone (rock-water system) no dissolution and predominating quartz-carbonate cementation.