Knowledge Bank

The Silurian Niagaran Dover 33 reef trend in the Michigan Basin has been injected with carbon dioxide for two decades to enhance oil recovery of the reservoir. This study examined the possible effects the injected carbon dioxide may have had on the Dover 33 reef over time. This was accomplished by examining three different intact cores from the edge of the Dover 33 reef from the region that was thought to have interacted with the gas plume to below the oil-water contact zone. Two different intact cores were analyzed by examining five different thin sections for pores, vugs, fractures, and secondary minerals. In addition, analysis of X-ray computed tomography data that were acquired from the two core samples prior to thin sectioning, plus a third before it had been disaggregated to reveal materials present in a large vug, was undertaken. Subsamples were extracted from the cores to measure δ13C values and to determine the mineralogy. The δ13C values revealed that carbonates were consistent with a Silurian seawater signal and there was no detectable reaction between the injected CO2 and the reservoir rock. This may indicate that porosity, pores, vugs, fractures, and secondary minerals are a result of primary deposition and subsequent diagenesis. Within this study, as depth increases, porosity, pores, vugs, and organic matter tended to decrease. There was no relationship determined between fractures and depth. Further research is needed to confirm this relationship between depth and these features within the reservoir. This study could serve as a baseline for this region of the reservoir for future assessments when the injected carbon dioxide reaches or has measurable effects on the reef.