ABSTRACT: Evaluation of Clastic Diagenesis Using Coupled Kinetic and Equilibrium Models

Ronald C. Surdam, Donald B. MacGowan, Thomas L. Dunn

Many of the diagenetic reactions that are volumetrically important to porosity evolution in sandstones are mediated by organic-inorganic interactions. These mediated reactions include the precipitation of clay and carbonate mineral cements and the dissolution of aluminosilicate and carbonate minerals. The relative concentrations of carboxylic acid anions and aqueous carbonate species, along with the timing of the generation and destruction of the carboxylic acid anions, act as first-order controls on the relative timing of these diagenetic events. Thermodynamic equilibrium-type computer models with enhanced organic-inorganic reaction data bases and temperature-extrapolated reaction equilibrium constants commonly are used to determine the direction and extent of water-rock interactions. However, changes in the concentrations of reactive organic species through time must be modeled using measured kinetic parameters and time-temperature burial history models. We have coupled these two modeling techniques, using a version of SOLMINEQ.88, which runs on a PC compatible, and the Diagenetic Advisor, a wholly PC-supported thermal maturation/kinetic modeling program. The results of this approach to modeling the evolution of diagenetic systems yield information on the relative stabilities of mineral phases through time, the timing of the generation of reactive aqueous and gaseous organic phases, and the timing of diagenetic events such as cement precipitation and grain dissolution. In this manner the evolution of primary, moldic, and microporosity in the reservoir s stem can be more accurately evaluated.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990