Basic Research Needs for Geosciences - Energetics Meetings and ...

PANEL REPORT: MULTIPHASE FLUID TRANSPORT IN GEOLOGIC MEDIAImaging of geomechanical processes and propertiesUnderstanding complex geomechanical processes will require accurate measurements of stress,pore pressure, deformation, alteration to the solid matrix, and rock fracturing at a variety ofscales, from the microscopic to the field scale. Available field-scale methods for imaging stressfields and deformation are limited by poor spatial coverage, particularly in three dimensions.Microscopic imaging of pore geometry and alteration of the solid matrix are limited by thesample size, spatial resolution of micro-tomography facilities, and experimental difficultiesassociated with creating controlled, representative and dynamic conditions needed formeaningful experiments in small experimental cells. Novel methods of in situ chemical imagingshould also be explored to reveal complex behavior at fluid-matrix interfaces.Flow and transport properties of seals, faults, and fracturesThe sealing quality of cap-rock formations, including any faults or fractures, is arguably the mostcritical element controlling the vertical migration of overpressurized or buoyant fluids in thesubsurface. These barriers to fluid flow typically consist of massive consolidated clay-richsediments (shale) and evaporites such as anhydrite. Resistance to flow results from the small sizeof the pore and pore throats (nano- to submicron-scale) in the rocks, creating both viscous andcapillary barriers to the nonwetting fluid during multiphase flow.The quality of a seal depends not only on the texture of rock matrix, but also on faults, fracturesand wellbores that penetrate the seal. Understanding the effectiveness of seals requires anintegrated understanding of the microscopic interfacial stresses at fluid-fluid and fluid-solidinterfaces, as well as a broader understanding of the depositional and postdepositional processesthat created the modern-day architecture of the seal. Natural oil and gas seeps associated withhydrocarbon reservoirs around the world demonstrate the imperfection of many natural reservoirsystems; these may be unacceptable in technological applications.The presence of an oil or gas reservoir provides proof of the existence and effectiveness of asealing formation, given that both oil and gas are buoyant relative to water. However, identifyingstrata that are effective seals for natural gas or CO 2 storage in brine-bearing formations, whichhave no apparent history of oil or gas residency, is a significant challenge. Basic research toidentify the relevant pore-scale physics, long-term reaction rates, and response to pressure andfluid evolution, as well as the development of measurement techniques to identify small features(like fractures) within subsurface domains, will facilitate the success of large-scale undergroundstorage of buoyant fluids such as CO 2 . A concerted program of basic research addressing thefollowing scientific areas is needed:• Understanding the impact of interfacial and surface properties of fluids in fine-grained andfractured media at laboratory, reservoir, and regional scales and at slow transport andreaction rates• Identification of the transmissivity of faults and fractures as a function of fluid chemistry,phase state, rock-fluid interactions, and pressure• In situ measurement of fluid-rock interactions in fine-grained media (saturation, pressure,and flow)• Identification and characterization of local high-permeability features in seals over largeregional scales18 Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems