| The development of unconventional reservoirs provides new challenges to the petrophysicist;
challenges that might be overcome with new techniques and approaches. The application of
electro-kinetics to hydrocarbon reservoirs is relatively recent. In fact, up until 2012 there was
no theoretical model that was capable of predicting the streaming potential coefficient of a
rock with given petrophysical properties (Glover et al., 2012). Here, we use that model to
ask the question whether the measurement of electro-kinetic properties of tight
gas sands and gas shales could be useful in the development of these resources.
We have calculated the streaming potential coefficient for gas shales with typical
values of porosity, cementation exponent and grain size as a function of pore fluid
salinity (10-5 to 2 mol/dm3) and pH (pH 5-9) at the temperatures and pressures
encountered in shale gas reservoirs. For typical gas shales such as the Barnett shale (grain
diameter 0.1 μ m, porosity 2.5 % and 5 μ D, respectively) the streaming potential
coefficient is less than 2Ã10-10 V/Pa for all the modelled salinities and pHs. This is
extremely small, and would only result in a streaming potential of the order of millivolts
even during hydraulic fracturing at 10 kpsi, while deep monitoring of fluid flow
would be impossible. Similar modelling of typical tight gas sands (grain diameter 3
μ m, porosity 5 %, permeability 0.1 mD) provides a higher streaming potential
coefficients, reaching 10-7 V/Pa at low salinities ( |