Carbon dioxide enhanced oil recovery from the Citronelle Oil Field and carbon sequestration in the Donovan sand, southwest Alabama

Abstract

Capturing carbon dioxide (CO₂) from stationary sources and injecting it into deep underground geologic formations has been identified as a viable method for reducing carbon emissions to the atmosphere. Sedimentary rocks, such as sandstones overlain by shales or evaporites, are the preferred formations because their morphology and structure provide pore space, and containment for the long term storage of CO₂. Sandstone formations have also served as repositories to migrating hydrocarbons, and are the sites of many oil recovery operations. For many depleted oil reservoirs, secondary waterflooding recovery methods are no longer efficient or economically viable, hence the application of tertiary CO₂ enhanced oil recovery (CO ₂-EOR) followed by CO₂ storage is an attractive and cost effective business plan.

Citronelle Oil Field, located in southwest Alabama, is the largest and longest producing sandstone oil reservoir in the state, having produced more than 170 million barrels of oil from its estimated 500 million barrels of original oil in place, since its discovery in 1955. The field is in the later stages of secondary recovery by waterflooding and daily oil production has declined considerably. The field is comprised of the Upper and Lower Donovan hydrocarbon bearing sandstones, which are separated by the saline-water-bearing sandstones of the Middle Donovan. The Ferry Lake Anhydrite, which overlies the three sections, serves as their caprock.

The present work is focused on an investigation of the feasibility of a CO₂-EOR project for the Citronelle Oil Field and the use of the Middle Donovan for long term CO₂ storage. A set of static calculations, based on estimation methods which were retrieved from publications in the field, was followed by computer simulations using MASTER 3.0, TOUGH2-ECO2N, and TOUGHREACT. Results using MASTER 3.0, for simulation of CO₂-EOR, indicated that nearly 50 million barrels of additional oil could be produced by tertiary recovery. Results using TOUGH2-ECO2N and TOUGHREACT, for the simulations of CO₂ storage, indicated that 159 million metric tons (175 short tons) of CO₂ could be stored in the Middle Donovan formation. An investigation into possible CO₂ leakage from the reservoirs indicated that the Ferry Lake Anhydrite serves as a very reliable long term storage seal.

The present work can serve as a template for preliminary assessment of tertiary oil recovery and CO₂ storage of similar oil reservoirs and saline-water formations.