Mineralogical responses of siliciclastic carbonate-cemented reservoirs to steamflood enhanced oil recovery

• Published in: Applied geochemistry Vol. 13; no. 4; pp. 491 - 507
• Main Authors: Keith, David C., Harrison, Wendy J., Wendlandt, Richard F., Daniels, Eric J.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.06.1998; Elsevier
• Subjects: Earth sciences; Earth, ocean, space; Exact sciences and technology; Geochemistry; Soil and rock geochemistry; reservoir rocks; minerals; authigenic minerals; Vapor; Siderite; High temperature; Permeability; Experimental study; Quartz; High pressure; Chemical equilibrium; Precipitation; Kaolinite; fluid-rock interaction
• ISSN: 0883-2927; 1872-9134
• DOI: 10.1016/S0883-2927(97)00082-6

Rock–fluid interactions induced by steamflood enhanced oil recovery were investigated in laboratory simulations to determine the geochemical reactions and the effects of these reactions on reservoir permeability. Flow-through laboratory experiments using mixtures of quartz, kaolinite, and siderite were performed in a high temperature/high pressure permeameter at a confining pressure of 1200 psi and temperatures between 150–250°C. Fluid compositions used in the experiments simulated the vapor and residual liquid phases encountered in steamflood operations as well as an intermediate fluid composition. Effects of fluid pH, fluid salinity and flow rate were systematically investigated in the experiments. The most extensive fluid–rock interactions were observed in the vapor phase simulations and high temperature/high pH condition simulations. Smectite, chlorite, illite, mixed-layer clays, greenalite, analcime, and K-feldspar were all identified as products of rock fluid interaction in the experiments. Smectite was the dominant authigenic phase to reduce permeability in the experiments. The experiments showed that the formation of smectite in Fe-rich environments does not require a clay precursor. Smectite is likely the most damaging neoformed mineral to reservoir permeability under different hydrogeochemical conditions for several reasons including: (1) its relatively high surface area (including microporosity in the “honeycomb texture”), (2) its propensity to migrate and block pore throats during fluid flow in porous media because of its small particle size, pore-lining texture, and electrochemical surface properties, and (3) the wide range of stability of smectites in the physical and chemical conditions that exist in reservoirs undergoing steamflood EOR. The rapid precipitation of authigenic minerals in these experiments suggests that the period required for fluids and rock to reach equilibrium in diagenetic environments are extremely short when considering geologic time scales. The armoring of pre-existing minerals by grain-coating authigenic minerals appears to result in the attainment of local equilibrium conditions prior to when one would predict assuming a continuous supply of reactant minerals was present.