The Relationship Between Fluid-Flow Systems and Sandstone Diagenesis in Laramide Basins

Ronald C. Surdam

Presently, fluid-flow systems characterizing reservoir sandstones in Laramide basins are regionally highly compartmentalized. Typically, down to a depth of 6,000 to 10,000 feet, the sandstones are under strong water drive and are dominated by a single phase fluid-flow system. Below 6,000 to 10,000 feet depth, the sandstones tend to be hydrocarbon-saturated (depletion drive) and dominated by a multiphase fluid-flow system. Pressure characteristics of the sandstones within these two regional compartments can change dramatically over short distances. In the upper hydrodynamic compartment, the sandstones can be hydrostatic, overpressured (artesian flow), or even underpressured. Sandstones at the top of the underlying hydrocarbon-saturated compartment tend to be normally press red or underpressured; within the compartment the sandstones are usually overpressured, but can be underpressured. In contrast to the regional framework, the dimensions of local compartmentalization of individual sandstones are determined by the geometry of the stratigraphic, structural, and diagenetic elements.

The degree of diagenetic alteration of sandstone petrophysical properties is strongly affected by the pathway a sandstone takes through fluid-flow space. The hydrodynamic compartment is usually characterized by large scale through-going mass transfer, whereas the hydrocarbon-saturated compartment tends to be a closed system with only local redistribution of mass; In Laramide basins the dynamic evolution of the fluid-flow system during burial; and subsequent uplift and erosion impacts sandstone diagenesis as much as increases in temperature or pressure, as the fluid flow system determines the potential for and scale of mass redistribution (i.e. porosity preservation, enhancement, or destruction).

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995