Overpressure in sedimentary basins: Mechanisms and mineralogical implications.

摘要

Overpressured compartmentation in sedimentary basins is explored with particular emphasis on sealing mechanisms and inorganic alteration due to fluid flow through seals. A new kind of capillary seal is described and experimentally verified. This sealing mechanism involves the presence of two fluid phases in layered sediments. The flow of both fluid phases is blocked by capillary forces. The implications and consequences of this sealing mechanism on the large-scale fluid flow in sedimentary basins are explored and discussed.; An inorganic alteration model [Cathles, 1991, Cathles and Shea, 1992] and the equations of state required to calculate the Gibbs free energy of aqueous species [Helgeson and Kirkham, 1976] are reviewed. New algorithms are presented that allow the prediction of the equation of state coefficients as functions of fundamental thermodynamic properties (i.e. standard state entropy, charge, and structure). Calculations that simulate the inorganic alteration due to fluid flow through temperature, pressure, and salinity gradients typical of sedimentary basins are presented and discussed.; The implications of this work are far-reaching. If gas capillary seals are operating in sedimentary basins, a new perspective on fluid flow through basins must be adopted. The ability to empirically predict the fundamental thermodynamic properties of aqueous species allows the estimation of parameters where experimental data does not exist and may provide insight into the fundamental nature of electrolytes.