Quartz Cementation along Cataclastic Fault Zones: Quantitative Modeling and Exploration Implications for Hydrocarbon Recovery

Wilfrido Solano Acosta¹, Andrew R. Thomas¹, Robert H. Lander², Robert M. Reed³, and Marek Kacewicz^1
1Chevron, Houston, TX
²Geocosm Ltd., Austin, TX
³Bureau of Economic Geology, The University of Texas, Austin, TX

In recent years, oil exploration has focused on more complex, less-well understood reservoirs. Owing to the scarcity of well control in such reservoirs, predictive models (e.g., Touchstone) have gained considerable attention to unravel reservoir porosity and permeability. Detailed and carefully collected geologic data coupled into these models, has proven very effective in reducing the uncertainty associated with exploration into unknown areas.

A well in the Gulf of Mexico was used to model the effects of diagenetic quartz cementation. Information was gathered from both deformation bands and adjacent undeformed zones. The work flow included collection of core descriptions, petrographic modal analyses, and high-resolution scanning electron microscopy (SEM) elemental maps along with acquisition of cathodoluminescence (CL) images that were digitally processed for mineral identification. Extensive digitization resulted in a suite of composite images representing the areas with and without deformation. The undeformed areas were modeled to represent a ‘normal’ cementation process. The deformation bands were modeled separately to quantify the contrast in quartz cementation rate between the deformed and undeformed zones.

Results from the Touchstone models suggest that a combination of low activation energy (52.2 kJ/mol) and relatively recent deformation can represent the measured quartz cement from deformation bands, in contrast to the undeformed rock which indicates a higher quartz cement activation energy (56 kJ/mol). The studied samples indicate that despite significant cementation occurring along deformation bands, the temperature and timing were not sufficient to destroy the reservoir properties. However, more intense cementation observed along deformed zones compared to those along undeformed areas may account for reservoir compartmentalization in other basin settings.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas