GOALI: The use of logging and surface NMR measurements to estimate hydraulic conductivity in unconsolidated aquifers

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THE USE OF LOGGING AND SURFACE NMR MEASUREMENTSTO ESTIMATE HYDRAULIC CONDUCTIVITY IN UNCONSOLIDATED AQUIFERSRosemary Knight (PI), Stanford UniversityYi-Qiao Song (Co-PI), Schlumberger-Doll ResearchThere are growing concerns, worldwide, about the sustainability of our groundwater resources. The critical decisions that must be made, in order to manage and protect our water resources, require accurate characterization of the properties of groundwater aquifers that govern both the storage and movement of water. The focus of this research project is the use of NMR (nuclear magnetic resonance) logging and surface-based NMR as a means of determining hydraulic conductivity (K) in the saturated zone of an unconsolidated aquifer from measurement of NMR relaxation times. NMR logging involves lowering an instrument into a borehole to measure the NMR relaxation times of hydrogen protons in the pore water of the surrounding geological material. NMR logging has been used for many years for petroleum applications to estimate the properties of petroleum reservoirs such as water-filled porosity, pore-size distribution, and permeability. There is now a growing interest in the use of NMR logging for groundwater applications to obtain estimates of K in unconsolidated or weakly consolidated aquifer materials. A key question to be addressed in our research: How can we obtain reliable estimates of K from NMR logging measurements in unconsolidated aquifers?Over the past decade, there has been great interest in a new, and very different way of making NMR measurements using Earth?s magnetic field and a system located at the surface. A non-invasive, surface-based NMR method, referred to as magnetic resonance sounding (MRS), has been developed and used to measure the NMR response of groundwater aquifers and obtain estimates of K. There are two outstanding questions related to this technology that will be addressed in this research: What is actually measured as the parameter currently taken to represent the NMR relaxation time in the MRS measurement? How can we obtain reliable estimates of K from MRS measurements in unconsolidated materials? Our vision, and the motivation for the research, is the development of a new approach to NMR-based aquifer characterization that 1) is grounded in an improved understanding of the relationship between the NMR response and K of unconsolidated materials and 2) builds on the best of both technologies in an integrated way. Our approach will allow us to explore new ways of integrating the two forms of NMR measurement to obtain improved subsurface models of NMR properties, and of K. Our proposed research includes laboratory experiments and numerical modeling. In addition, we will conduct a field experiment near Lexington, Nebraska where both logging and surface-based NMR measurements will be made over the 90 to 120 m thick Ogallala aquifer. This proposal represents a unique opportunity for collaboration by bringing together a research group at Stanford, with expertise in NMR laboratory measurements, theory and modeling; a research group at the U.S. Geological Survey with an ongoing project to study MRS; and key industrial partners, Schlumberger-Doll Research (SDR) and Schlumberger Water Services (SWS), with expertise in the acquisition and interpretation of NMR logging, and Vista Clara, Inc., with expertise in the acquisition and interpretation of MRS data.