ABSTRACT: CO₂ Huff 'n' Puff Recovery Feasibility as Function of the Effect of CO₂ on Mineral Stability in a Dakota Sandstone Reservoir, Central Wyoming

Leta K. Smith, Donald B. MacGowan, Ronald C. Surdam

The high pressures required for CO₂ injection in Huff 'n' Puff treatment have the potential to destabilize carbonate minerals in the formation. Scaling problems caused by precipitating cements may occur after production resumes. However, the presence of sufficient organic acid anion buffers may stabilize carbonate minerals at high P_CO2, causing them to precipitate from the formation waters and block pore throats. Modeling these conditions for individual reservoirs is important in the design of the Huff 'n' Puff treatment in order to avoid formation damage or production-line clogging.

Based on our modeling, we predict that in the Huff 'n' Puff treatment on this Dakota sandstone reservoir, scale buildup in the production line will not be a significant problem. The CO₂ injection pressures expected (1100-2000 psi) are sufficiently high to keep carbonates in solution. No formation damage is expected because there is little carbonate cement in this Dakota sandstone reservoir to dissolve and reprecipitate in the pore throats after pressures decline. Also, organic acid anions are in sufficiently low concentration (3.56 meq/L) that they cannot buffer the pH; thus carbonates will not precipitate with increased ^SgrCO₂, especially since calcium concentrations are also low (26 ppm).

These predictions will be tested when this Huff 'n' Puff treatment is initiated. Test results will provide refined input data (especially pressure data) for modeling future treatments. The predictions and test results presented will then be used to improve the predictive capability of the modeling process.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990