--> Abstract: Quantifying the Evolution of Pore Networks in Dolomites Using Petrographic Image Analysis Techniques, by T. T. Mowers and D. A. Budd; #90987 (1993).

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MOWERS, T. T., and D. A. BUDD, Department of Geological Sciences, University of Colorado, Boulder, CO

ABSTRACT: Quantifying the Evolution of Pore Networks in Dolomites Using Petrographic Image Analysis Techniques

Late-stage cementation is an important aspect of porosity evolution in some dolomites. Although petrographically obvious, the quantitative significance of such cements on pore networks may be difficult to evaluate. To this end, we developed a petrographic image analysis (PIA) technique that quantifies porosity and permeability reduction in dolomites due to late-stage cementation. The technique is demonstrated using two dolomite reservoirs with varying amounts of late-stage calcite cements: Little Sand Draw (LSD) field, Wyoming, and Bindley field, Kansas.

Pore area and specific pore surface of the extant pore network were measured from thin sections of core plugs; permeability of the plugs was also measured by conventional means. An empirical expression relating all three parameters was derived using the Kozeny-Carmen equation. Next, calcite cement was discriminated from the same images and analyzed as pore space; this effectively backstrips the calcite from the extant pore network to yield the precursor pore network. Pore area and specific pore surface of the precursor system were then input to the previously derived Kozeny Carmen expression to estimate the permeability of the pre-calcite pore system. Calcite cement was found to be insignificant in LSD dolomites; it resulted in less than a two-fold change in permeability. In contrast, the effect of cementation in Bindley dolomites was a 100-fold decrease in permeability and the localized destruction of reservoir-quality rock. The difference between the two results is the occlusion of small vs. large pore throats in LSD vs. Bindley dolomites, respectively. These data demonstrates the utility of our technique relative to pore-network evolution in dolomites. To our knowledge, this is the first application of PIA to the evolution of pore systems.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.