Occlusion of Porosity in Carbonate Reservoirs by Dickite: ABSTRACT

Abstract

Significant amounts of the clay mineral dickite have been found in Lower Cretaceous carbonate rocks of the Maverick basin and in Middle Permian (Guadalupian) carbonate rocks of the Permian basin. Dickite was precipitated in secondary cavities within limestones and dolostones, and in many intervals porosity has been massively occluded. In most voids, precipitation of dickite was preceded by calcite or dolomite cements. In both the Maverick and Permian basins, dickite occurs in carbonate rocks that contain abundant anhydrite. Because dickite is associated with early stages of carbonate diagenesis, it is inferred to have been emplaced near the surface or at shallow depths. In Permian carbonate rocks of the Permian basin, individual dickite crystals are very large (for clay), ranging up to 180µ in diameter. Dickite crystals occur in large hexagonal platelets. In thin sections most dickite platelets have been transected perpendicular--or at some angle other than parallel--to basal crystal faces; thus individual crystals appear as fibers, and platelets appear as fan-shaped or polygonal fibrous which closely resemble chalcedony. Fibrous aggregates of dickite are length-slow and are easily misidentified as length-slow chalcedony. In Middle Permian carbonate rocks of the Permian basin, much of the material identified as length-slow chalcedony probably is dickite. When fluids are artificially forced through dickite-bearing carbonate rocks, individual layers can be disaggregated from the platelets and interconnected pores may be blocked by dislodged dickite crystals. In well-stimulation methods, great care must be taken to prevent this migration of fines. End_of_Article - Last_Page 474------------