Translation of geophysical log responses to estimate subsurface hydrogeologic properties at the Hanford 300 Area

The geology and chemistry of the subsurface environment are fundamental factors controlling contaminant fate and transport, and thus play a critical role in remediation efforts at DOE sites. However, the subsurface is often heterogeneous and not well characterized. Petrophysical models that relate borehole neutron and gamma ray data to reservoir properties such as clay content, matrix density, porosity, and permeability are critical in the formation of meaningful reactive transport models. The objectives of our research are to: (1) analyze core and outcrop samples from representative facies for a variety of mineralogical, chemical and physical properties, (2) predict the response of a variety of neutron and gamma logging tools based on these measurements, (3) develop algorithms to translate log responses into formation properties useful for input in flow and reactive transport models such as matrix density, lithology, porosity, and permeability. Our analysis of selected core samples from Hanford well 399-3-18 (C4999) reveals significant correlations between K, Th, and U concentrations and both matrix density and total clay, as determined by pycmometry and Dual Range Fourier Transform Infrared spectroscopy, respectively. Based on these relationships, we developed algorithms to predict total clay and matrix density from existing spectral gamma logs. The availability of laboratory bulk density data allows us to compute porosity estimates for our sample set. The comparison of clay content and porosity reveals a relationship that is consistent with the relationship observed by Marion et al. (1992) and others, suggesting the existence of both clay-supported and framework (or grain) supported domains and the ability to estimate porosity from clay content. Further, the availability of total clay, matrix density, and porosity permit application of the k-Lambda model as a means to estimate permeability. These results, although limited, suggest the path towards developing additional algorithms to predict these important properties from existing logs. Analysis of selected samples from Hanford well 399-2-26 (C6210), located within the Hanford 300 Area Integrated Field Research Center (IFRC), indicates that the relationships between K, Th, and U concentrations and both matrix density and total clay closely match those observed in C4999, suggesting that the algorithms developed will be generally applicable to the large number of logs collected in the Hanford and Ringold formations. We are in the process of analyzing additional core samples from wells distributed within 300 Area IFRC 399-3-31 (C6214), 399-2-30 (C6217), and 399-2-31 (C6218) and deeper wells from the surrounding Hanford_300 Area for which both geophysical logs and bulk density measurements are available - 399-1-23 (C5000), 399-3-19 (C5001), and 399-3-20 (C5002). Based on these new data, we will present refined algorithms for matrix density, clay content, porosity and permeability.