Abstract
Monitoring of potential gas seepage for CO2 sequestration and CO2-EOR (Enhanced Oil Recovery) in geologic storage will involve geophysical and geochemical measurements of parameters at depth and at, or near the surface. The appropriate methods for MVA (Monitoring, Verification, Accounting) are needed for both cost and technical effectiveness. This work provides an overview of some of the geochemical methods that have been demonstrated to be effective for an existing CO2-EOR (Rangely, CA, USA) and a proposed project at Teapot Dome, WY, USA. Carbon dioxide and CH4 fluxes and shallow soil gas concentrations were measured, followed by nested completions of 10-m deep holes to obtain concentration gradients. The focus at Teapot Dome was the evaluation of faults as pathways for gas seepage in an under-pressured reservoir system. The measurements were supplemented by stable carbon and oxygen isotopic measurements, carbon-14, and limited use of inert gases. The work clearly demonstrates the superiority of CH4 over measurements of CO2 in early detection and quantification of gas seepage. Stable carbon isotopes, carbon-14, and inert gas measurements add to the verification of the deep source. A preliminary accounting at Rangely confirms the importance of CH4 measurements in the MVA application.
Highlights
Gas seepage can occur by several mechanisms and can follow a variety of pathways [1].The reservoir pressure during injection can exceed the capillary entry pressure of the caprock.The probability of this increases non-linearly with pressure increase and differs for specific gases.This work focuses on leakage up pre-existing faults that serve as a pathway for fluid migration.The fault may be charged with gas, as free CO2, CH4, and light hydrocarbons
The Test Site is located on Precambrian high grade metamorphic rocks that can be considered a background for soil gas and flux measurements
The method for selecting locations for 10-m holes to allow nested sampling was described in the Materials and Methods section
Summary
Gas seepage can occur by several mechanisms and can follow a variety of pathways [1].The reservoir pressure during injection can exceed the capillary entry pressure of the caprock.The probability of this increases non-linearly with pressure increase and differs for specific gases.This work focuses on leakage up pre-existing faults that serve as a pathway for fluid migration.The fault may be charged with gas, as free CO2 , CH4 , and light hydrocarbons. Gas seepage can occur by several mechanisms and can follow a variety of pathways [1]. The reservoir pressure during injection can exceed the capillary entry pressure of the caprock. The probability of this increases non-linearly with pressure increase and differs for specific gases. This work focuses on leakage up pre-existing faults that serve as a pathway for fluid migration. The fault may be charged with gas, as free CO2 , CH4 , and light hydrocarbons. In the case of an old oil field planned for CO2 -EOR, there may be pre-existing wells whose location is not recorded and are not properly plugged and abandoned (P&A). Carbon dioxide is soluble in water and may migrate with deep groundwater flow. An important fact with regard to solubility is that CH4 is much less soluble in water, maintaining a gaseous state, and is much more mobile in a chemically reducing subsurface environment
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
