Carbon capture and sequestration (CCS) is regarded as a feasible strategy for reducing large volumes of anthropogenic CO2 emissions. Although the purpose of geologic carbon sequestration is to trap CO2 in the subsurface, there is a risk that the injected CO2 will migrate away from the primary target formation and migrate to the surface. To monitor the possibility of CO2 leakages at the near-surface, a background database predating injection is first established. Follow-up surveys of a repetitive nature are conducted to identify at an early stage any surface seepages relating to open conduits such as improperly plugged wells and fractures/faults. CO2 plumes of less concentration emanating from target sites are slower and can take years to reach the surface in any significant amounts. A reliable and effective monitoring system is an important part of making geological sequestration a safe and acceptable method for the permanent disposal of CO2.

It should be noted that potential sites for sequestration should be screened by soil gas surveys for their storage suitability. Preliminary surveys can save a great deal of time and resources, and can optimize planning. Petro-Find can provide consultation services in this regard.

ECBM PROJECTS

Petro-Find soil gas surveys can be adapted for Enhanced Coalbed Methane (ECBM) Projects. Repetitive very high-density surveys for Methane could prove to be a major tool for showing the lateral extent and direction of gas flooding fronts extending from the central injection well to the production wells. The released Methane from gas flooding moves laterally along the coal bed in the direction of the highest permeability and lowest pressure. It is reasonable to expect that the Methane migrates upwards as well though the hanging wall of the coal seam to the surface where it can be detected by soil gas surveys. It should be noted that Methane is reported in surface water wells in Wyoming CBM projects.

The gas front composed of Methane and CO2 may exhibit an elliptical pattern with the long axis parallel with face cleats. Lineaments or faults may serve as either conduits or barriers for the gases. Facies changes in the coal seam are also mitigating factors. The directional (anisotrophic) permeability of the cleat system and its control of gas fronts as it moves laterally along the coal seam have major implications for the spotting and timing of production wells.

CO2 MISCIBLE FLOODING PROJECTS

Petro-Find technology can be applied to CO2 Miscible Flooding projects (EOR), which is finding increasing application for tertiary recovery of oil reservoirs. Repetitive very high-density surveys for CO2 and light hydrocarbons could prove to be a major tool for showing the lateral extent and direction of the CO2 flooding fronts extending from the central injection well to the production wells.

It is entirely reasonable to expect that CO2 injected under high pressure in an oil reservoir will exhibit vertical migration through micro-fractures. The molecular weight of CO2 is about the same as Propane, which can easily escape along with heavier Butane to the surface. With flooding, open fractures can act as major conduits for CO2 and light hydrocarbons from the oil reservoir to the surface. Alternatively, closed fractures can act as barriers to the sweeping action of CO2 and a damming effect is likely to be observed.