Recognition and Contribution of Deep-Burial Diagenesis to Porosity Evolution in Carbonate Reservoir Rocks: ABSTRACT

Abstract

Porosity and permeability develop in carbonate rocks by several processes, including preservation of primary pores, secondary pore formation as a result of dissolution of grains and cements, and dolomitization. Secondary porosity formation most commonly is postdepositional and occurs in environments from subaerial meteoroic (eogenetic) to deep burial, the latter involving fluids of meteoric, connate, or hydrothermal character. In the past, reservoir formation models have been dominated by analogy to studies of diagenesis and porosity occurrence in shallow meteoric environments. However, porosity occlusion and formation are amply documented in deep-burial diagenetic settings in ancient rocks, and such environments are known to exert predictable controls on the evolution of hydrocarbon reservoirs. Pore types created in such settings commonly mimic those in eogenetic environments to the extent that recognizing specific diagenetic environments of reservoir formation is not possible through the petrographic study of pore systems alone. Recognizing the deep-burial origin of porosity in hydrocarbon reservoirs can contribute much to predictions concerning possible porosity trends in the subsurface. Petrographic studies combined with comparative stable isotopic and trace element distributions in rock components are the most reliable means of tracing porosity evolution in deep burial diagenetic environments.