Shaly sand formation evaluation in tight gas sands using electrochemical potential measurements
Abstract
Equations are developed that directly relate the shaly conductivity to the electrochemical (membrane) potential (EP). The model is applied to both fully and partially saturated sands. The relationship between the resistivity index and the water saturation is also expressed in terms of a single membrane potential measurement. The Ep measured at different salinities are compared with model prediction using a single membrane potential measurement. Sigma (sub 0) versus Sigma (sub w) curves are then generated using the model equations and compared with measured curves. Experimental results are presented for electrochemical potential measurement made in the lab on 50 tight gs sand samples. It is shown that the measurements can be correlated with CEC although the CEC measured by grinding up the samples was always higher than that estimated from Ep measurements. The Ep measurements are combined with the equations for partial saturation developed in the report to obtain water saturations in a tight gas sand well. Through the example it is shown that it is possible to determine the water saturation in Shaly sands from one membrane potential measurement at a known salinity together with a set of resistivity logs. The results clearly demonstrate the applicability of the method as a practical procedure for Shaly sand information evaluation.
- Publication:
-
Topical Report
- Pub Date:
- August 1991
- Bibcode:
- 1991twdb.rept.....S
- Keywords:
-
- Electrical Measurement;
- Electrical Resistivity;
- Natural Gas Exploration;
- Sands;
- Clays;
- Electrochemistry;
- Salinity;
- Space Charge;
- Water;
- Geophysics