Publication Date:
2014-12-12
Description:
Geological sequestration of $${\mathrm{CO}}_{2}$$ for enhanced oil recovery (EOR) has been in use for decades, but it now represents a potentially economical method of mitigating anthropogenic $${\mathrm{CO}}_{2}$$ output. However, current understanding of the interaction between injected $${\mathrm{CO}}_{2}$$ and the reservoir rock is limited and prevents accurate estimation of reservoir $${\mathrm{CO}}_{2}$$ capacity. Delineating the diagenesis of the reservoir is useful in predicting post- $${\mathrm{CO}}_{2}$$ injection changes in reservoir porosity and permeability. The Albian Donovan Sand member of the Rodessa Formation, Citronelle Field, Alabama, is the subject of an ongoing Department of Energy $${\mathrm{CO}}_{2}$$ -EOR suitability study. The arkosic Donovan Sand is highly heterogeneous, containing conglomeratic intervals, low to extensive poikilotopic calcite cement, loose to tight grain packing, and low 〈1% to high (5%) porosity (primary and secondary) observed in thin section. It forms the basal members of laterally discontinuous upward-fining parasequences that define a marine to brackish to fluvial delta system. The diagenesis of the Donovan Sand occurred in five stages: 1) pre-burial and compaction–formation of extensive calcite cement; 2) partial dissolution of calcite cement and framework feldspars; 3) secondary calcite cementation, localized dolomitization, and calcite and anhydrite concretion formation; 4) hydrocarbon charge; and 5) pyrobitumen development. Primary porosity is dominant, but substantial secondary porosity was formed during stage 2. Following injection of $${\mathrm{CO}}_{2}$$ , water injection and oil and gas production rates dropped below modeled values. We propose that the $${\mathrm{CO}}_{2}$$ injection dissolved calcite cement proximal to the injection well and reprecipitated it nearby with the effect of reducing porosity and/or permeability.
Print ISSN:
1075-9565
Electronic ISSN:
1526-0984
Topics:
Geography
,
Geosciences
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