Monitoring, Verification and Accounting (MVA) Applied to CO2-EOR Projects
Previous geochemical measurements at three operational or proposed CO2-EOR projects; Rangely, CO, Teapot Dome, WY, Weyburn, SK are presented as indicators of effectiveness of selected MVA methods. Seasonal fluxes and soil gas concentrations of carbon-containing gases have been determined by the author at Rangely and Teapot Dome. Similar measurements were made at Weyburn by a group led by the British Geological Survey. Methane and light hydrocarbon measurements will be more effective than CO2 for monitoring of EOR projects, whereas CO2 measurements have dominated proposals at pure sequestration projects. Measurement of inert gases as indigenous tracers in soil gas and shallow ground waters for monitoring will be effective in both pure sequestration and CO2-EOR projects. Isotopic measurements provide stronger data necessary for verification. In climates with strong seasonal variations, carbon-containing gas fluxes can vary by a factor of ten and shallow soil gas concentrations by a factor three, primarily due to seasonality of shallow biological processes. Winter or dry season measurements allow improved recognition of a deep source component. Modeling of CH4 and light alkane vertical migration at Rangely indicated an estimated improvement of the signal:noise ratio by a factor of five during winter measurements. A first-order estimate of deep source gas leakage at Rangely is <170 tonnes of CO2 and 400 tonnes of CH4 annually. Trace CH4 leakage at Teapot Dome was detected over faults. An IPAC-sposored study over an alleged localized leak at Weyburn used carbon-contiaining gases to verify the absence of leakage at this location. The results support the particular strength of isotopic measurements on inert gases in shallow groundwater for purposes of verification.
AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013