Alumino-Silicate Dissolution in the Subsurface: Experimental Simulation of a Specific Geologic Environment: ABSTRACT

Abstract

The present study is an attempt to integrate the two in a simulation of diagenesis in the Stevens sandstone of the San Joaquin basin, California. Petrographic studies of the Stevens sandstone from North Coles Levee show extensive feldspar dissolution; the oil field brines from North Coles Levee contain as much as 2640 ppm difunctional carboxylic acids. Laboratory simulation of this specific geologic environment was performed using actual well brines and unaltered sands from the Stevens sandstone of North Coles Levee, as well as mineral grains and artificial brines. After leaving the feldspar grains for two weeks in a pressure vessel at 100/sup 0/C (approximate reservoir temperature), scanning electron microscope study revealed extensive dissolution textures similar to those noted in the well-core samples. Moreover, the aluminum concentration in the well brine was elevated by at least two orders of magnitude over saturation with respect to kaolinite by organometallic complexation of the aluminum. Other experiments showed calcite to be highly soluble in the brines as well. In summary, the feldspars and calcite of the Stevens sandstone appear to be in gross disequilibrium with respect to the organic constituents of the brines. The experiments suggest that the time scale over which these dissolutionmore » reactions occur is geologically instantaneous. The ubiquity of carboxylic acids in oil field brines suggests that this process of porosity enhancement may be generally operative in clastic sedimentary basins.« less