Abstract
Estimating water saturation via conventional logging tool such as resistivity cannot provide an accurate solution in a formation with low conductivity water and tight porosity. As an alternative, we employed a dielectric permittivity, which makes it easy to differentiate the water from the other fluids in pore structures. A multichannel frequency dielectric logging tool is used for measuring in situ permittivity. To simulate a dielectric permittivity, we used two analytic models: Lichtenecker-Rother (LR) and Stroud-Milton-De (SMD) models. The key goal of this research is to propose a workflow to evaluate an equivalent Archie’s parameter which can generate the same dielectric logging tool responses with core measurement results using a given analytic models. According to the results of the LR model curve-fitting, the estimated Archie’s parameter shows inversely proportional relationship with clay volumes. The estimated Archie’s parameter from the SMD model is sensitive to the lower frequency channels of the multifrequency dielectric logging tool. Nevertheless, utilizing the response of the dielectric logging tool in the frequency range, where interfacial polarization effect does not exist, can provide an alternative to estimate water saturation in shale formations with relatively less conductive waters.
Highlights
Accurate calculation of water saturation in a target formation is crucial for estimating the potential volume of hydrocarbon
We applied two different analytic models to demonstrate (1) which model is the most appropriate to calculate the dielectric permittivity in shale formations, and (2) which model provides more reliable Archie’s parameter combined with dielectric permittivity logs
We used a combined model (LR model and Archie) to calculate the dielectric permittivity and water saturation using 1 GHz frequency component; where the exponent of the LR model is identical to the cementation factor of the Archie’s equation
Summary
Accurate calculation of water saturation in a target formation is crucial for estimating the potential volume of hydrocarbon. When we apply the Archie’s equation for calculating water saturation, the cementation factor and tortuosity factor are measured in core samples that require numerous representative core samples of the formation. This measurement is not rigorous when dealing with tight formations that have a small pore volume. Geoscientists can convert the resistivity and conductivity information acquired by well logging to fluid saturation based on the given saturation model Another limitation of the conventional method for calculating water saturation is that the resistivity logging tool cannot differentiate water from hydrocarbon when the water is less conductive (or lower salinity). We validated the analytic model via tests on core samples and estimated Archie’s parameter in a field dataset
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