Holtz, Mark¹, Christine Doughty², Joseph Yeh¹, Susan Hovorka¹ 
(1) The University of Texas at Austin, Austin, TX 
(2) LBNL, 

ABSTRACT: Modeling of CO2 Saline Aquifer Sequestration and the Effects of Residual Phase Saturation

Petrophysical properties have a strong influence on how a plume of injected CO₂ will form and move in the subsurface. Permeability controls the direction and rate of CO₂ movement, and porosity and residual saturation control the size, shape, and dispersion. This research simulates the movement of sequestered CO₂ taking into account the effects of residual non-wetting phase saturation To examine CO₂ plume characteristics, petrophysical analysis was accompanied by 3D geocellular modeling as an input into fluid-flow simulator. Petrophysical algorithms were developed that captured the interrelationships amoung porosity, horizontal and vertical permeability, residual CO₂ saturation and wireline logs. These petrophysical algorithms were applied to develop a 3D geocellular aquifer model based on sandstone-body geometry. The resultant model was used to simulate CO₂ injection in a saline aquifer. Two base cases using constant low or high residual CO₂ saturation were compared with an algorithm employing variable residual saturation. In the latter model, the residual CO₂ saturation of each grid block depended on the initial CO₂ saturation of the grid block, resulting in hysteretic relative permeability and capillary pressure curves. During injection, the CO₂ plume was roughly radially symmetric, with permeability variability, depth, and buoyancy affects combining to create a tornado-shaped plume. During the post-injection period, the initial tornado-shaped plume is distorted by permeability variation, dip direction and residual saturation. Much greater dispersion of the CO₂ plume occurred when residual CO₂ saturation was low. Residual non-wetting phase saturation therefore is a key factor controlling long term sequestration.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.