ESTIMATING THE CO2 SEQUESTRATION CAPACITY OF DEEP SALINE AQUIFERS IN SOUTHWESTERN INDIANA

Today’s concerns about global climate change call for evaluation of many innovative proposals for reducing the amounts of greenhouse gases released into the atmosphere.  One such proposal is the sequestration of large volumes of CO₂ in subsurface reservoirs.  The MIDCARB Project (Midcontinent Interactive Digital Carbon Atlas and Relational Database), a consortium of five states (Illinois, Indiana, Kansas, Kentucky, and Ohio), is developing an interactive spatial database that will store information about large emitters of CO₂ (power plants, refineries, ethanol plants, etc.) and potential long-term geological sites for CO₂ sequestration, such as aging or abandoned oil and gas fields, coal beds, abandoned subsurface mines, unconventional oil and gas reservoirs, and deep saline aquifers.

 

The present study attempts to estimate the CO₂ sequestration capacity of the Silurian and Devonian aquifers in southwestern Indiana, deep brine-filled aquifers composed of carbonate rocks.  On average, connate waters in these aquifers contain 60,000 to 90,000 ppm total dissolved solids (TDS).  Porous zones within the aquifers occur in four stratigraphic intervals, two within the Devonian System, and two within the Silurian System.  Isopach and porosity distribution maps were created for each porous zone in southwestern Indiana to predict CO₂ storage capacity.  Porosity data were collected from porosity logs, particularly density/neutron and sonic logs. 

 

Based on porosity and thickness derived from geophysical well logs, three possible scenarios of total pore volume in the aquifer were evaluated.  The analysis of petrophysical data revealed minimum (0.27 trillion cubic feet - TCF), intermediate (0.62 TCF), and maximum (1.3 TCF) pore volumes available for CO₂ sequestration in the Silurian and Devonian aquifers of Indiana.  Because of the shallow depths of these aquifers, the sequestration of CO₂ will most likely occur under subcritical temperatures and pressures.  The interactions between the connate brines and CO₂ under subcritical conditions remain unstudied.  In particular, under such conditions, the effects of miscibility and compressibility of CO₂ on the brines require further investigation.