GIS METHODS FOR RESERVOIR ASSESSMENT AND ESTIMATING CO2 SEQUESTRATION CAPACITIES

Comparative evaluation of CO₂ sequestration capacity of continuous reservoirs is a task with much in common with classic subsurface resource analysis. Current research is concerned with screening subsurface reservoirs as candidates for sequestration and identifying those places where that reservoir has the best potential. Regionally distributed, continuous, low-permeability reservoirs, like organic-rich shales, coals, and saline reservoirs, are possible sequestration targets, but often lack the dense and detailed reservoir data available for oil and gas fields. Two examples of using ArcView GIS software tools to compile sequestration assessments are discussed.

In Kentucky, Devonian black shales underlie approximately two-thirds of the state and occur in both the Illinois and Appalachian basins. Using GIS tools, gridded thickness data were used to derive estimated tons of shale in place. Structure and isopach data were used to further limit that estimate to the aerial extent of shale that is at least 1,000 feet in depth and 100 feet thick. Using this final extent, measured CO₂ sequestration capacity in standard cubic feet per ton of shale was used to calculate total capacity by summing grid cells.

The Cambrian Mt. Simon is a saline aquifer distributed throughout Illinois, Indiana, Ohio, and the northern one-third of Kentucky. A conventional volumetric assessment was compiled using porosity, water saturation, CO₂ solubility, reservoir temperature and pressure, and other parameters. Limited data required modeling the distribution of many of these parameters. Depth to the midpoint of the reservoir was calculated from gridded structure, isopach, and digital elevation data. Using the midpoint depth data and typical subsurface gradients, continuous grids of reservoir temperature, pressure, porosity, and other parameters were estimated. These data were used to derive a volumetric estimate of CO₂ capacity by summing grid cells.