Direct and indirect assessment of vegetation located near CO2-mediated enhanced oil recovery (CO2-EOR) activities

Background/Question/Methods

This study examined the potential of vegetation monitoring to determine if there are local ecological effects of CO₂ mediated Enhanced Oil Recovery (CO₂-EOR). Injection of CO₂ into geological reservoirs containing crude reduces the viscosity and allows for the movement and recovery of crude that was previously cost prohibitive using other methods. CO₂ injection into geological reservoirs may also serve as a means to reduce atmospheric CO₂ through geological sequestration. However, monitoring and verification is essential to ensure that geological sequestration is effective and without negative effects to the surrounding environment. Monitoring of vegetation was accomplished using small scale, direct measurement, as well larger scale indirect measurements to determine whether CO₂-EOR activities impact surrounding vegetation. The direct, small scale component was accomplished by examining the basal area increase in plots located adjacent to oil field structures as well as control plots outside of the oilfield, before and after CO₂ breakthrough. Indirect larger scale measurements were used to look for stress in vegetation adjacent to the injection area as well as the larger oilfield area and areas just beyond. Normalized Difference Vegetation Index (NDVI) values for hardwoods, evergreen and mixed forest were determined by Land Use Land Cover (LULC) 2006 classification.

Results/Conclusions

Results of a before after control impact paired (BACIP) analysis of the basal area of plots indicate that there is no statistical significance between control and impact areas between all basal area, hardwoods, conifers and size for all plots after reported breakthrough. Some plots experienced high increase in percent growth. Two plots with a greater increase were subjected in part to logging activity and the growth may be attributed to an increase in available sunlight. This does not suggest influence of CO₂ on growth; however, it does suggest that additional observation and study are needed to separate influences of logging activity and potential CO₂ influence. Small differences in NDVI values are observed in both deciduous and mixed forest but these differences appear to be similar with respect to season. There were no differences observed in NDVI of evergreen forests. Overall, detrimental impacts on vegetation surrounding an EOR-CO₂ project were not observed at the scales of observation used in this study.