Reservoir fluid-rock interactions during a co₂ eor/ccs pilot test at citronelle oil field, alabama

Abstract

With the world’s expanding need for energy, new sources of petroleum or technologies to extend current petroleum reserves are required. However, concerns about global warming are increasing as atmospheric CO2 levels continue to rise worldwide due to the burning of fossil fuels. Enhanced oil recovery (EOR) provides a method for expanding existing petroleum reserves by prolonging the life of older oil fields where primary production methods have been exhausted. EOR also opens an avenue for using CO2 captured from point sources such as power plants for beneficial purpose, thus preventing its release into the atmosphere and sequestering the CO2 in deep geologic formations that also serve as petroleum reservoirs. Citronelle Oil Field, located in Mobile County, Alabama, was the site for a 2008-2012 SECARB pilot project funded by the U.S. Department of Energy (DOE) that was aimed at testing CO2 flood for enhanced oil recovery and carbon sequestration. Citronelle Field is the largest and oldest oil play in the state of Alabama with reserves originally estimated at about 500 million barrels in place, less than half of which had been produced between its discovery in 1955 and the start of the pilot project in 2008. The field’s primary producing units are the Upper and Lower Donovan Sands within the Rodessa Formation. The work performed for this study was funded by the DOE to examine the fluid-rock interactions induced in the reservoir by the injection of supercritical CO2. Water samples were collected from four production wells located around the CO2 injection well between June 2010 and February 2012, and water chemistry was analyzed by ICP-OES and IC. Temporal trends for water sample compositional variation are presented, and compositional similarities and differences between the water samples collected from the four wells are discussed. Geochemical modeling was employed to determine the fluid-rock interactions taking place within the reservoir and thus provide potential explanations for the observed water sample compositional trends. Finally, the impact of an over pressuring event that created preferred flow paths within the system and its impact on water chemistry and oil production is discussed.