Basin Modeling and Diagenetic Effects of Groundwater Migration

Xavier Guichet¹ and Sylvie Wolf^2
1Geology-Geochemistry-Geophysics, IFP, Rueil-Malmaison, France
²Applied Mathematics, IFP, Rueil-Malmaison, France

Our objective is to trace the volume of minerals that precipitate or dissolve in a sedimentary basin as groundwaters migrate along temperature and pressure gradients. In a sedimentary basin, temperature and pressure changes can occur in response to burial and exhumation or changes in heat flow. On the other hand, in a steady-state flow regime (T and P do not change with time), cementation only results from hydrologic mass transport. Our calculation is based on the assumption that minerals maintain local equilibrium with migrating groundwaters and their solubilities depend only on temperature and pressure. Thus every temperature and pressure change known by groundwater, leads to a precipitation or a dissolution of the mineral in order to preserve local equilibrium. We developed a prototype based on Temis3D® Software, which is a coupled numerical simulation program that evaluates pore pressure, porosity, overburden and other petroleum parameters through time. Our prototype uses built-in solubility correlations to calculate solubilities of a large collection of minerals as a function of temperature and pressure. Finally the cementation or dissolution rate of a mineral is calculated in each cell of the basin model by solving a mass balance equation that describes transport of the dissolved mineral by advection. The prototype predicts cumulative volume changes of minerals following instantaneous rates of precipitation and dissolution, and highlights area where cementation processes are expected to occur. Since our model does not take into account more complex geochemical factors that might control mineral precipitation or dissolution such as reaction kinetics or mixing fluids of differing composition, quantitative estimate of volume changes of minerals must be interpreted with caution.

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