ADSORPTION OF ORGANIC-COMPOUNDS ON CARBONATE MINERALS .3. INFLUENCE ON DISSOLUTION RATES

This is the third in a series of papers to investigate the role of organic compounds on wettability, porosity and permeability of carbonate rocks. These are important reservoir characteristics that influence the performance of petroleum reservoirs. This paper reports dissolution studies to address diagenetic effects on carbonate porosity and permeability. Comparative dissolution measurements were performed to assess the influence of adsorbed organic material on the reactivity of calcite and dolomite in the geologic environment. Organic compounds that adsorb strongly on carbonate minerals (fatty acids and carboxylated polymers) were found to dramatically inhibit dissolution, while weak adsorbates and nonadsorbates showed little or no effect on the dissolution rates. Experiments were performed at 20-degrees, 50-degrees and 80-degrees-C to examine the role of organic adsorbates at reservoir temperatures, and the strong adsorbates inhibited dissolution at all temperatures. Experiments from various initial pH's confirmed that strong adsorption is an ionic interaction and demonstrated that the inhibition of dissolution is limited to pH's above 4.5-5.