Abstract: Effect of Diagenetically Derived Texture on Petrophysical Properties of Dolomite

Robert E. Woody, Jay M. Gregg, Leonard F. Koederitz

Dolomites commonly show significant variation in crystal textures that result from exposure to different diagenetic environments. Two basic textural types of dolomite exist: (1) planar dolomite which forms in shallow and burial diagenetic environments; and (2) nonplanar dolomite which develops at elevated temperature (>600°C), in the burial environment, by dolomitization of limestone or recrystallization of pre-existing dolomite.

Late Cambrian dolomites were collected from core and outcrop throughout Southeast Missouri. Effective porosity and permeability was determined using helium porosimetry and gas permeametry. Total porosity as well as texture type was determined from thin sections. Pore throat geometry was evaluated using mercury capillary pressure curves and SEM examination of pore casts.

Two porosity-permeability populations exist in planar dolomites: (1) permeability that strongly varies with porosity, and (2) permeability that does not significantly vary with porosity. In the first population capillary pressure data and SEM pore cast analysis indicate uniform pore throat size and well interconnected pore systems. Such systems do not exist in the second population, possibly due to cementation. Nonplanar dolomite shows no significant correlation between porosity and permeability. Capillary pressure and pore cast studies of nonplanar dolomite indicates nonexistent to very poorly interconnected pore systems. Pore casts show that pore throats have sheet-like geometries in both planar and nonplanar dolomites, however in the latter throats tend to be much more convoluted.< P>

This study suggests that understanding diagenetic history, and the crystal textures that may result, can be a predictor of petrophysical properties of dolomite reservoirs.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994