Influence of Diagenesis on Porosity Development in Reservoir Sandstones--An Overview

Richard E. Larese

Chemical and physical diagenetic processes have greatly influenced porosity development in reservoir sandstones. Taken individually, diagenetic factors serve to decrease, preserve, and in some instances increase porosity. Commonly these processes are interrerlated, and the effects of one may be partially or completely offset by the effects of another. In many sandstones, preburial factors including tectonic setting, provenance, and depositional facies have exerted significant control over diagenetic environments and trends. In addition, diagenetic environments are influenced greatly by the effects of time, temperature, pressure, and pore-water composition with burial.

The most prevalent diagenetic effect in sandstones involves porosity reduction by cementation and compaction. Overall, principal cementing agents consist of quartz, carbonate, and clay. Correspondingly, considerable porosity loss can be attributed to physical and chemical compaction by grain rotation, ductile grain deformation, and pressure solution. Commonly the development of detrital and authigenic grain coatings in quartzose sandstones has served to preserve (relative sense) intergranular pore space by inhibiting silica in pore waters from nucleating on detrital quartz surfaces as quartz overgrowths. Petrographic evidence suggests that clays, in particular chlorite, constitute the most common and important coating types affecting quartz cementation. Selective dissolution of detrit l and authigenic mineral constituents has significantly increased porosity of many reservoir sandstones. Although considerable pore space may be attributed to chemical removal of carbonate as cement/mineral replacements, significant porosity enhancement can develop by direct dissolution of detrital framework constituents (e.g., feldspar, volcanic rock fragments). Although dissolution of silicate mineral components results in increased porosity, it does not necessarily result in enhanced permeability.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.