Rock/water
reactions are largely a function of formation mineralogy and (if
applicable) cement composition. Pore-water chemistry and pore-water
residence also significantly influence rock/water reactions. Land
and Macpherson (1992) summarized the composition of Miocene sandstones
in the Gulf Coast, showing that they are the most immature and potentially
reactive in our study. Published data are available from outcrop
studies of the Fleming Formation to the west (Ragsdale, 1960). Ragsdale's
data show that the sands are primarily composed of quartz, carbonate
rock fragments, and chert. Sediments of these outcrops were probably
deposited in a more fluvial environment that those of the subsurface
in the Texas City area, and so mineralogic differences may exist.
Potential for significant interaction with CO2-rich fluids
appears moderate. Samples from four wells in Galveston county that
include the Lagarto/Oakville interval are available for mineralogical
analysis at The University of Texas at Austin, Bureau of Economic
Geology, Core Research Center, if the need arises for more detailed
investigations of rock/water reactions in the Texas City area. A
limited number of pore-fluid chemistry data for the Miocene interval
of Galveston County are available in the Core Laboratories (1972a).
13
Reference:
Core
Laboratories, 1972a, A survey of the subsurface saline water of
Texas: Volume 2 chemical analysis of saline water: Texas Water Development
Board, Report 157, 378 p.
Land,
L. S., and Macpherson, G. L., 1992, Origin of saline formation waters,
Cenozoic section, Gulf of Mexico sedimentary basin: American Association
of Petroleum Geologists Bulletin, v. 76, p. 1344–1362.
Ragsdale,
J. A., 1960, Petrology of Miocene Oakville Formation, Texas Coastal
Plain: University of Texas, Austin, Master's thesis, 196 p.
