Integration of surface and logging NMR data to map hydraulic conductivity

Abstract

Geophysical NMR measurements yield direct detection of groundwater and provide sensitivity to hydraulic conductivity (K) via the measured NMR water content and relaxation times. The aim of this work is to map hydraulic conductivity over wide areas by leveraging complementary aspects of surface and logging NMR measurements. Surface NMR measurements have the advantage of being non-invasive and can image the basic NMR response of the subsurface over wide areas. NMR logging measurements, on the other hand, provide data at higher resolution and detail, but can only be acquired at sparse locations where boreholes are available. In practice, deriving robust estimates of K from either of these measurements is improved using site-specific calibration and comparison with hydrogeologic K measurements. We have developed a framework for calibrating and integrating these measurements, and this framework has been tested at three field sites in the United States. The framework can be divided into three components: (1) establishing the relationship between the logging NMR measurement and hydrogeologic measured K; (2) establishing the relationship between the logging NMR and surface NMR measurement; and (3) relating the surface NMR measurement to K and extending surface acquisition over a wide area. The data include an extensive collection of slug-tests, NMR logs, and surface NMR measurements, supplemented further by (DP) technologies, including a pressure/flow sensor DP-K tool and novel DP-NMR tool. Our results demonstrate the viability of this approach as well as the need for appropriate site- or region-specific calibration. Specifically, the relationship between the NMR logging measurement and surface NMR measurement can vary significantly in the presence of magnetic geology. We have also established that the method of well installation and logging can influence the estimated relationship between the NMR log and K measurement.