On Prediction of Reservoir Quality Through Chemical Modeling

Indu D. Meshri

Although useful descriptive models of reservoir diagenesis have existed for some time, the goal of this symposium is to investigate chemical-mathematical modeling approaches to reservoir diagenesis. I believe substantial progress toward this objective can be achieved by blending the experiences of classical petrologists, chemical modelers, engineers, and formation water geochemists at this symposium. Distillation of petrologic and experimental work has given us insight into the controls on porosity. Thus, the input parameters to coupled models include rock composition, rock texture, water composition, water-rock ratio, pressure, and temperature.

Chemical models (speciation-solubility models) are able to provide prediction of late-stage cements where formation water chemistry data and thermodynamic data on minerals are reliable. Chemical models (reaction-path models) are useful in simulation of diagenetic sequences where fluid flow is minimal and the rock-water system can be considered closed. Coupled models (chemical reaction models coupled with physical mass transfer models) can be used to predict mineral distribution in space and time and are applicable to open systems.

An advantage of diagenetic simulations through geochemical modeling is that they are much faster than empirical predictive models based on numerous petrographic observations. Another advantage is that many scenarios of provenance and burial history can be tried. Aside from such applications to exploration, chemical models are beneficial in simulating possible formation damage during enhanced oil recovery and other production operations.

Despite this progress, we must be cautiously optimistic about chemical models because of the lack of reliable thermodynamic data (e.g., aluminum species) and paucity of kinetic data on mineral dissolution and precipitation rates. In understanding the implications of chemical models to exploration, we must support further work on thermodynamic and kinetic data for commonly occurring detrital/authigenic minerals in sedimentary rocks.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.