Effects of carbon dioxide on sandstone reservoir quality
- Colorado School of Mines, Golden, CO (United States)
Core-flood experiments were conducted using subarkosic Weber Sandstone (Rangely Field, Colorado) to quantify dissolution processes of carbonate cements as a function of temperature, pressure, fluid salinities, and CO{sub 2} fugacities typical of hydrocarbon reservoirs. Experimental results are consistent with fluid chemistry and petrographic observations of secondary porosity attributed to corrosive fluids in natural sandstones. Dolomite and/or calcite are the dominant authigenic cements. Experimental temperatures were 75 and 100{degrees}C, pore pressures were to 230 bars, and confining pressure was 300 bars. The flooding fluids were 0.25 and 0.5 molal NaCl solutions containing up to 0.3 molal CO{sub 2}. Preliminary geochemical modeling indicates pH values were about 3 to 4 under experimental conditions. Initial effluent fluids contain high Ca{sup 2+} and K{sup +} concentrations (up to 1000 and 60 mg/L, respectively) that decrease with experimental duration. Effluent concentrations of Mg{sup 2+} increase with time in dolomite-cemented samples but decrease in calcite-cemented samples. High initial concentrations of Ca{sup 2+} are interpreted to reflect dissolution of outer calcium-rich cement rims and smaller cement crystals . With additional fluid, magnesium-rich cement cores and larger crystals are attacked. Petrographic examination of post-experiment core plugs shows cement dissolution is more effective near the inlet end. Isolated, heterogeneously distributed carbonate cements in the more porous and permeable laminae are attacked more readily than poikilotopic cements in finer-grained, less porous and permeable laminae. Cement crystal morphologies indicate dissolution occurred by initial breaching of the outer zones, followed by preferential dissolution of less-resistant zones or cores.
- OSTI ID:
- 425655
- Report Number(s):
- CONF-960527-; TRN: 96:004994-0293
- Resource Relation:
- Conference: Annual convention of the American Association of Petroleum Geologists, Inc. and the Society for Sedimentary Geology: global exploration and geotechnology, San Diego, CA (United States), 19-22 May 1996; Other Information: PBD: 1996; Related Information: Is Part Of 1996 AAPG annual convention. Volume 5; PB: 231 p.
- Country of Publication:
- United States
- Language:
- English
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