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Characterizing Reservoir Quality of Niagaran Pinnacle Reefs using Salt Plugging Signatures Defined by Pulsed Neutron Capture Logs


The Midwest Regional Carbon Sequestration Partnership (MRCSP1) large-scale test involves assessment of CO2 EOR and Storage in depleted oil fields in the northern fairway of Michigan's Niagaran Pinnacle Reefs. A comprehensive field data collection effort is underway to support the characterization, monitoring, and modeling objectives of the program. The individual reefs/oil fields are in various stages of production: pre-EOR, active EOR, and late-stage EOR. One aspect of this work has focused on the analysis of Pulsed Neutron Capture (PNC) logs to better characterize the reservoirs. These Silurian aged reefs represent prime production and CO2 storage reservoirs. Excavation of these tight gas reservoir reefs traditionally target a carbonate, the Brown Niagaran (or Guelph) formation, stratigraphically situated below the A-2 Evaporite and A-1 Carbonate, which contains well-developed intercrystalline and vuggy porosity. The overlying A-1 Carbonate and A-2 Evaporite consists of interfingered partially dolomitized carbonate and evaporite layers. Potential reservoirs within this part of the stratigraphic column can have varied degrees of salt plugging which plays a role in the hydrocarbon storage capacity and overall productivity in a reef. Traditional monitoring and analyzing techniques of these reservoirs are potentially problematic due to through-casing evaluation limitations. As a result, PNC tools are optimal for characterizing salt plugging within and above the Brown Niagaran and for monitoring and characterizing reservoir conditions.

PNC tools are ideal candidates for identifying salt plugging due to high sensitivity of chlorine signatures associated with NaCl (halite) evaporites. Chlorine in halite formations bombard the PNC tool detectors and create high capture cross section (Sigma) responses. These highly chlorine sensitive detectors produce significant signatures that can be used to identify the presence of salt plugged intervals. These intervals represent prime locations for modeling and characterization of CO2 reservoirs. Analysis of these salt plugging signatures were correlated with 3D seismic and cross section data to produce 3D static earth models. These models were incorporated into reservoir characterization and monitoring of production and CO2 zones.

This project is funded by DOE-NETL under DE-FC26-0NT42589 and conducted with Core Energy, LLC as the host company.