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

PANEL REPORT: MULTIPHASE FLUID TRANSPORT IN GEOLOGIC MEDIAInterfacial and surface properties of fluids in fine-grained and fractured mediaFine-grained materials lead to slow flow rates for single-phase fluid flow due to the high viscousresistance (low permeability) associated with the small pore spaces. In multiphase flow, capillaryentry pressures may preclude a non-wetting fluid (like CO 2 ) from entering the pore spaces,thereby eliminating flow through the formation. However, heterogeneity of material properties,small-scale features like fractures, and the interplay between buoyancy, pressure, and interfacialforces (capillarity), make this invasion and subsequent flow of fluids like CO 2 through finegrainedmaterials highly uncertain and difficult to predict (see the sidebar on Buoyancy,capillarity, and heterogeneity: Buoyancy-driven flow at all scales). Possible reactions associatedwith fluid-solid interfaces can modify any invasive flows that develop (e.g., Johnson et al. 2004).All of these feedbacks and nonlinear processes must be understood in the context of flowsuppression and leakage control to properly characterize and quantify the movement of injectedfluids through sealing formations.Transmissivity of faults and fracturesIn addition to detection and characterization of the properties of faults and fractures at highspatial resolution, it is critically important to be able to predict whether faults will transmit orretain fluids as a function of fluid pressure, phase state, and chemical composition. A majorsource of uncertainty and disagreement centers on whether fault systems are sealing ortransmissive. Even if the initial character of a fault system is known, anthropogenic perturbationscan change its properties. Available wellbore-based characterization tools are either poorly suitedor completely inadequate for characterizing these effects. Fault gouge properties and complex3D fracture networks in natural systems are very difficult or impossible to reproduce in alaboratory setting, making field measurements a critical but expensive and time-consumingaspect of this research. Finally, the typically slow rate of fluid migration in these structuresmakes conducting measurements in a timely manner challenging, even under favorableconditions.In situ measurement of fluid-rock interactions in fine-grained media (saturation, pressure andflow)The performance of fine-grained barriers in multiphase conditions is complex because the activesealing mechanism varies with fluid composition and pressure, and the changes in geochemicalbehavior and stress can alter the properties of the seal. Tests of seal properties in the laboratoryor from the wellbore are inherently limited in terms of their spatial coverage and validity whenextrapolated to in situ pressure and temperature conditions. Improved field-deployable methodsare required for accurate determination of the properties of flow barriers. If these measurementscould be made in situ without major modification of the natural environment, then observationsof seal properties as functions of changing fluid composition, pressure and stress duringanthropogenic perturbations could be made.Identification and characterization of local higher-permeability features in sealsTechniques to identify the existence of sealing strata, and to a lesser extent sealing faults, arecurrently available. However, techniques to locate and then quantify the properties of the weakBasic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems 19