These changes are consistent with ion exchange from clay surfaces and clay mineral transformations and suggest that early fixation of K from seawater can lead to early illite formation. Experiments relate mineral reactions to measurable, observable phenomena. In EAGL, a controlled experimental approach is taken to mineral growth and dissolution rates by direct measurement in known solution chemistries, at different reaction times and temperatures. Walter s group is currently determining reaction rates for feldspar alteration, quartz precipitation and salt recrystallization. Fluid salinity and organic acid content have major roles in the rate of feldspar dissolution as well as in the formation rate of secondary clay minerals.
Quartz precipitation is more rapid as the fluid salinity increases.
These experiment results can be related back to rock products and burial histories resulting is a useful blend of chemistry with geologic factors to better explain natural reservoir porosity and permeability. Sedimentary basin fluids reveal different hydrologic histories. The composition of subsurface waters can be a vital indicator of directions of fluid flow, amount of interaction with host rocks, and type of freshwater recharge history a given rock reservoir has experienced. Members of the EAGL group have sampled and analyzed the chemistry of formation waters in many sedimentary basins with active hydrocarbon exploration and production. For example, the Michigan Basin has shale and salt aquitards interlayered with porous sandstones and carbonates.