Effect of Texture on Petrophysical Properties of Dolomite: Evidence From the Cambrian-Ordovician of Southeastern Missouri
Two basic textural types of dolomite exist: (1) planar dolomite, which forms in both shallow and burial diagenetic environments; and (2) nonplanar dolomite, which develops at temperatures in excess of 50°C in the burial environment by dolomitization of limestone or neomorphic recrystallization of preexisting dolomite. Variation in dolomite texture is the result of variation in the diagenetic history of the rock unit. Cambrian-Ordovician dolomites were collected from core and outcrop throughout southeastern Missouri. Effective porosity and permeability were determined using helium porosimetry and gas permeability. Total porosity and texture type were determined from thin-section analysis. Pore throat geometry was evaluated using mercury capillary pressure curves and scanning electron microscope (SEM) examination of pore casts. Two porosity-permeability populations exist for planar dolomite: (1) planar-e (euhedral) dolomite, where permeability strongly varies with porosity; and (2) planar-s (subhedral) dolomite, where permeability is lower than in planar-e dolomite and does not increase as rapidly with increasing porosity. In planar-e dolomite, capillary pressure data and SEM pore cast analysis indicate uniform pore throat sizes and well-interconnected pore systems. Uniform throat sizes and well-connected pore systems do not exist in planar-s dolomite. This most likely is due to continued cementation during diagenesis. Nonplanar dolomite shows no significant correlation between permeability and porosity. Capillary pressure curves and SEM examination of pore casts of nonplanar dolomite indicate nonexistent to very poorly interconnected pore systems and large pore to throat ratios. The petrophysical properties of dolomite petroleum reservoirs and aquifers vary depending on the petrographic texture of the dolomite. Understanding diagenetic history and crystal textures that may result because of various diagenetic conditions, can be a predictor of petrophysical properties of dolomite reservoirs.
R. E. Woody et al., "Effect of Texture on Petrophysical Properties of Dolomite: Evidence From the Cambrian-Ordovician of Southeastern Missouri," AAPG Bulletin, vol. 80, no. 1, pp. 119-132, American Association of Petroleum Geologists (AAPG), Jan 1996.
Geosciences and Geological and Petroleum Engineering
Keywords and Phrases
Cambrian; Diagenesis; Dolomite; Ordovician; Petrophysical Properties; Rock Texture; USA, Missouri
International Standard Serial Number (ISSN)
Article - Journal
© 1996 American Association of Petroleum Geologists (AAPG), All rights reserved.