The spectral electrical responses [Formula: see text] of sand and clay mixtures subjected to an effective stress of [Formula: see text] and saturated with varying concentrations of NaCl are measured in a laboratory environment in the frequency range [Formula: see text]. Changes in clay content and fluid concentrations result in characteristic changes in amplitude and phase spectra. The equivalent circuit model due to Dias is used to characterize the spectral electrical behavior of the saturated mixtures. Two circuit elements of Dias model, the electrochemical parameter [Formula: see text], and the dimensionless parameter [Formula: see text], are particularly sensitive to the amount of clay and the concentration of the pore fluid. The electrochemical parameter [Formula: see text] is shown to increase significantly with an increase in clay content when the soil sample is saturated with freshwater. The dimensionless parameter [Formula: see text] on the other hand is directly related to the concentration of the pore fluid solution (NaCl), increasing with an increase in fluid concentration. Effects of electrode polarization on the [Formula: see text] measurements are modeled and minimized by addition of a Warburg diffusion element term to the equivalent circuit model of the sample.

A procedure is developed to estimate the hydraulic conductivity and porosity of soils from the laboratory measurements of their frequency dependent electrical response (FDER) using inversion schemes and regression models. The FDER (resistivity and phase spectra) of a soil contains valuable information about its porosity, hydraulic conductivity, texture and fluid properties. In this study the FDER of the soil is modeled as a heterogeneous system using the multi-Cole-Cole model. The intrinsic parameters, which innately describe the response of the multi-Cole-Cole model, are retrieved by an inversion scheme and are used in empirical regression models to predict the hydraulic conductivity and porosity. Measurements of hydraulic conductivity, porosity and spectral electrical response of a variety of soil samples at laboratory scale were also performed. Multiple regression analyses suggest that the porosity and permeability can be well predicted by the parameters of the multi-Cole-Cole model. Establishing such direct relationships between parameters characterizing the spectral electrical response of soils and their hydraulic properties may provide a versatile non-invasive methodology of obtaining hydraulic conductivity and porosity of soils using geophysical measurements. This study is the beginning of a new class of geophysics that links the flow properties to the geophysical data.

The spectral electrical responses (SER) and hydraulic properties of clean sands saturated with deionized water and subjected to varying stress levels in a laboratory environment are investigated and analyzed. A variation of the multi-Cole-Cole dispersion model that predicts the behavior of the SER of sands is suggested for the analysis. This dispersion model is described by circuit elements [Formula: see text], the bulk resistivity, chargeability [Formula: see text], time constant [Formula: see text], and exponent [Formula: see text], representing various conduction mechanisms. The values of [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text], which describe the SER are directly affected by changes in the applied stress and the attendant changes in hydraulic properties: porosity and hydraulic conductivity. It is observed that changes in the hydraulic properties of the sands due to changes in the applied effective stress are related to the circuit parameters characterizing this model. In general, a decrease in porosity results in an increase in the relaxation time constant [Formula: see text]. The rate of increase in [Formula: see text] is higher for variable size sands than for monosize sands. The time constant is generally greater for larger monosize sands than for smaller monosize sands, and thus [Formula: see text] may be related directly to the mean grain size. Changes in the applied effective stress are shown to result in changes in the chargeability of the soils. The chargeability [Formula: see text] of the soil decreases with increases in hydraulic conductivity [Formula: see text] and porosity [Formula: see text]. Increases in [Formula: see text] and [Formula: see text] tend to increase the frequency dependence exponent [Formula: see text] of the soil.

With the maturity of and demand for fiber-optic sensing technology growing steadily over the last few years across multiple basins, operators are seeking fiber-optic sensing solutions that address the technology challenges associated with the life-of-field monitoring of subsea developments. Single-ended distributed temperature sensing (DTS) measurements have been acquired for decades now, typically using Raman optical time-domain reflectometry (OTDR) on multimode fiber. However, for topside interrogation of subsea completions, Raman DTS performs poorly. This is due to the available optical power budget and the potential wavelength dependency of optical attenuation across multiple connectors and splices comprising the optical subsea infrastructure. Any wavelength-dependent attenuation as the signals pass through connectors, splices, and optical feedthrough systems will generate step changes in the measured Raman DTS temperature profile. Brillouin OTDR can provide a DTS alternative that overcomes these challenges and operates on single-mode fiber. Brillouin OTDR operates with a large dynamic range to measure a wavelength (frequency) shift of the Stokes/anti-Stokes components that is proportional to both strain and temperature. Since downhole cables are manufactured with optical fibers suspended in a gel and with appropriate extra fiber length (EFL), any fiber strain relaxes, and the Brillouin wavelength shift is an absolute temperature measurement. An additional alternative is also explored here. We typically associate coherent Rayleigh OTDR with distributed acoustic sensing (DAS) on single-mode fibers, but low frequencies also contain a relative temperature dependence. The low-pass filtering of DAS data can then be used as a form of Rayleigh DTS with appropriate data processing. In this paper, we report on a comparison of Raman, Brillouin, and Rayleigh DTS simultaneously acquired in the same high-rate producer and injector wells. We validate that, with appropriate cable design, Brillouin DTS can be simultaneously operated on the same single-mode fiber with DAS and can deliver absolute temperature measurements suitable for production analysis. We also use a laboratory experiment to show that Rayleigh DTS provides an accurate measure of temperature changes comparable in precision to a traditional thermocouple. We conclude with a discussion about the implementation of this DAS-DTS solution for sensing subsea completions.