Carbon Dioxide Fluxes in a Forest Soil in the Citronelle Oil Field of South Alabama

Latasha Lyte and E.Z. NyakatawaDepartment of Natural Resources and Environmental Sciences Engineering Sciences, Alabama A&M University,

Normal, Alabama 35762ABSTRACT

Forest soils play a major role as terrestrial sources or sinks of CO2. The main sources of soil CO2 fluxes are decomposition of organic matter and respiration from roots and associated soil fauna. Soil is the largest terrestrial sink of atmospheric C, containing about 1500 Pg of C worldwide. Geological sinks in forest soils of south Alabama have a huge potential for sequestering billions of metric tons of CO2 through enhanced CO2 oil recovery (EOR). Enhanced CO2 oil recovery offers an opportunity to safely and permanently store CO2 in natural carbon sinks such as brine-filled geological formations and compounds such as lime (CaCO3 and CaCO3.MgCO3), thereby reducing the atmospheric concentration of this greenhouse gas. In order for the concept of geological sequestration of CO2 injected into oil wells to be environmentally sound, it is important that the CO2 being injected into the ground will not escape back into the atmosphere. This paper discusses baseline soil CO2 fluxes in a forest soil around five oil wells before CO2 injection for EOR in the Citronelle Oil Field in south Alabama between August 2008 and March, 2009. Soils CO2 fluxes at all the wells were highest in August 2008 with values ranging from 0.53 to 2.28 mg CO2 m-2 min-1. These values declined significantly with decrease in soil temperatures from August 2008 to March 2009. The soil was a NET sink of atmospheric CO2 at well B-19-10-1 in September 2008 and October 2008, and at well B-19-10-2 in March 2009. Our data show that the soils around the wells at the study location are deficient in soil C from 15cm depth and below, hence a potential for geological sequestration.

RESULTS AND DISCUSSION Soil CO2 fluxes were highest in August as indicated in Fig. 1 . This can be

attributed to microbial activity in the surface layers of forest soils which had a significant amount of organic C. The average pH around the wells was 4.50. This is typical for soils under pine forests that are deficient in basic cations such as Ca, Mg, and K (Fig. 2). Surface soils at the site have a high electrical conductivity of 5 Sm-1 (Fig. 3). There is a low amount of C sequestered in the soils. Since the C in forest litter is exposed to the atmosphere instead of being buried, it can be lost as CO2. Sub-soils around the wells are very deficient in total N (Fig. 4) and total C (Fig. 5). Highest concentrations of N and C were found in the top 0-5 cm due to forest litter (Fig. 4 and Fig. 5)

INTRODUCTIONCarbon dioxide is a major greenhouse gas that causes global warming

(Wu and Chan, 2009). CO2 is easily generated by human activities through burning of fossil fuels and wood (Pielke, 2009). Combustion of fossil fuels in the transportation, industrial, commercial, and residential sectors in the Southeastern U.S. makes this region a major contributor to the nationwide anthropogenic CO2 emissions (Pashin et al, 2005). Separation of CO2 from combustion products followed by storage in geologic formations is one of the most promising approaches to reducing CO2 that accumulates in the atmosphere as a result of human activity and natural processes.

REFERENCESPashin, J. C., J.W. Payton, and M.G. Gates, Geological Survey of Alabama, Carbon Sequestration Research, Southeastern Regional Carbon Sequestration Partnership (SECARB Phase I), http://portal.gsa.state.al.us/CO2/SECARB1/SECARB1.htm#Techtrans, 2005.

Pielke., Roger A. Jr. 2009. An idealized assessment of the economics of air capture of carbon dioxide in mitigation policy. Environmental Science & Policy. 12:216-225.

Wu, Yuxiang and Christine W. Chan 2009. A data analysis decision support system for the carbon dioxide capture process. Expert with Applications. 36:9949-9960.

MATERIALS AND METHODS

CONCLUSIONSoils around wells at the study site are acidic with high E.C. and are deficient in

both C and N. High soil CO2 fluxes around the wells indicate significant biological activity in top layers of the forest soil in August 2008 compared to September and October 2008.

ACKNOWLEDGEMENTSFunding for this project is provided by the U.S. Department of Energy, grant no. DE-FC26-06NT4302 and

supported by Title III. Figure 1. Soil CO2 fluxes from forest soils around oil wells, Citronelle, AL

OBJECTIVES1) To measure soil CO2 fluxes in a forest soil around CO2 injection and producer oil wells

2) To investigate sub-surface vertical migration of CO2 around CO2

injection and producer oil wells

3) To measure C storage and soil properties of soil around injection and producer oil wells

Study LocationStudy is being done in the Citronelle oil field, Mobile County, AL. The

area consists of loblolly pine forest . Five wells-one injector well and four producer wells are being used in the study.

Equipment for soil gas, soil moisture and soil temperature

Figure 4. Total N in forest soils Figure 5. Total C in forest soils

Figure 2. pH of soils at oil wells in June 2008, Citronelle, AL Figure 3. EC of forest soils in June 2008

Study site of showing pine forest

Data being collected1. Soil pH and electrical conductivity (Acumet LX 20 pH/conductivity meter

(Fisher Scientific Inc) 2. Soil C and N – LECO TruSpec CN analyzer3. Soil CO2 fluxes – (Varian CP3800 GC)

Gas Sampling

Varian CP 3800 GC for gas samples Soil C and N analysis