Comparing Arrays for Induced Polarisation Surveys in a Saline Environment

Conventional arrays for resistivity and induced polarisation (IP) surveys were developed before multi-channel switching systems and modern inversion algorithms allowed more complex and flexible data acquisition geometries. Though some work has been done exploring the optimisation of resistivity arrays (Furman et al. 2003a, 2003b &Stummer et al. 2004), less has been done for IP surveys (White et al. 2003). Using a ten channel recording system, several IP surveys were conducted using Wenner, dipole-dipole and non-conventional arrays with the aim of exploring which array type gave the best data quality, reproducibility and coverage. In addition, a four second injection interval was compared with a two second interval. The surveys were carried out at a legacy oil refinery site that has weathered hydrocarbons near the surface and extremely saline conditions. Preliminary results show that the reciprocal measurements with the Wenner array are more reproducible than those with the dipole-dipole array. As well, the decay curves for the four second injection interval follow theoretical decay curves more closely than those for the two second interval. Optimising survey array design is needed to meet the challenges posed by a growing interest in the use of induced polarisation for environmental site characterisation.