Abstract: Self-Developed and Self-Enhanced Pressure Seals: Application of the CIRF.A Reaction-Transport Computer Simulator

Yueting Chen, Kenneth Sundberg, Peter Ortoleva

A generic mechanism for the development and maintenance of pressure seals is proposed that involves a positive feedback. The pressure dependence of reactions can lead to precipitation from a fluid as it moves down a pressure gradient. Precipitation in a given zone will decrease permeability there and in turn focus the overall pressure gradient in that zone. The augmented local pressure gradient promotes an even greater rate of precipitation in the zone of the original precipitation.

Conditions favoring quartz versus calcite cementation sealing are delineated, as are controls on seals due to initial sedimentology, pressure maintained across the seal, and fluid salinity and temperature. Effects of other minerals and organic phases are also discussed.

Computer simulations show that through the above mentioned mechanism, pressure seals can develop from certain sedimentary seal precursors and automatically maintain lateral continuity. Once a pressure seal forms, the mechanism can heal the fractures caused by basin deformation or overpressure.

The simulations are carried out using CIRF.A, a general reaction-transport computer simulator. CIRF.A accounts for chemical reactions between minerals and fluids and within fluids, the growth, dissolution and nucleation of minerals, and the coupling of flow and mineral reactions through texture dependent permeability. It predicts the mineralogical evolution of a two dimensional domain in response to given inlet fluid composition, pressure and temperature. The code has corrections to the activities of aqueous species due to fluid composition, temperature and pressure and corrections to equilibrium constants due to pressure changes.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994