REACTION-TRANSPORT SIMULATION OF DIAGENESIS USING WRIS.TEQ: DIFFUSION ENHANCEMENT OF HETEROGENEITY AND BULK-ROCK DIAGENETIC TREND

Enhancement of sediment heterogeneity due to transfer of solutes across sediments has been previously demonstrated by us using WRIS.TEQ, and by others using simpler mass-transfer-enabled water-rock interaction simulators, in recent years. In this study a number of bulk-composition diagenesis simulations are carried out in which one sediment packet represents the average composition of several sediment layers. In addition diagenesis of individual unaveraged sediment layers is simulated using diffusive mass-transfer.

Compositions and burial histories of layered sediments are derived from published literature. Bulk compositions of the layered sediments are obtained through volume-averaging sediment layer compositions. More than 14 minerals are used to characterize the sediments. Both the layered sediments and the average bulk sediment are subjected to the identical burial history. No water was allowed to enter or exit either system to control the total mass.

Simulations are carried out using WRIS.TEQ, a quantitative diagenesis simulator that can emulate sediment compositional and textural evolution over geologic time in response to changing thermal and fluid compositional conditions. Using a unique composite-media approach, the simulator accounts for textural and compositional evolution of multi-mineralic heterogeneous sediments according to kinetic and thermodynamic reactions between water and minerals, and diffusive and advective mass-transfer of solute.

The primary benefit of the bulk-composition approach is that the results can be used directly to correlate with observed average behavior of sediments, and the simulation time is a mere fraction of that required for the layered sediment systems. The layered sediments approach, by providing more detailed mineralization patterns, can be used to assess more accurate reservoir characteristics.

Both approaches also demonstrate the importance of mass-transfer with the surrounding material , i.e., the influx and efflux of water from deeper sediment, etc. Thus, the next task is to evaluate above diagenetic systems subject to more complex water flux histories.