Temperature-dependent streaming potentials: 2. Laboratory

Streaming potentials and zeta potentials were measured at equilibrium conditions, while at elevated temperatures of 23degrees - 200 degreesC and pressures of 20 MPa, on intact rock samples of Fontainebleau Sandstone, Berea Sandstone, and Westerly Granite using the oscillatory data collection method. The streaming potential coupling coefficient for Fontainebleau Sandstone decreased in magnitude from 195 nV/Pa at 23 degreesC to 33 nV/Pa at 160 degreesC before rising to 41 nV/ Pa at 200 degreesC. The Berea Sandstone coupling coefficient decreased in magnitude from 100 nV/ Pa at 23 degreesC to 23 nV/ Pa at 160 degreesC and then increased in magnitude to 100 nV/ Pa at 200 degreesC. The Westerly Granite coupling coefficient increased in magnitude from 23 nV/ Pa at 40 degreesC to 68 nV/ Pa to 120 degreesC, then decreased in magnitude to 43 nV/ Pa at 160 degreesC, and then increased in magnitude to 50 nV/ Pa at 200 degreesC. The zeta potential for all three samples increased in magnitude with increasing temperature, during these equilibrium experiments, which did not mirror the coupling coefficient responses. The temperature dependence of the zeta potential provides indications of possible chemistry changes occurring within sample, such as pH, ionic concentration, and ionic composition. These experiments confirm that knowledge of rock/solution chemistry is important for modeling coupling coefficients and zeta potentials. Results of the experimental work are compared to a model that predicts zeta potential variation with temperature, and reasonable correlations are obtained.