Stress Dependence of Sandstone Electrical Properties and Deviations From Archie’s Law

Topics: Reservoir characterization

The resistivity index (RI) of Fontainebleau and Bentheimer sandstones was investigated at ambient and reservoir pressures down to low water saturations. The RI measurements show that both sandstones display Archie behavior at elevated pressure. However, at ambient pressure, the RI for Fontainebleau sandstone deviates from Archie behavior at low water saturations. The pore-space images suggest that the deviation from Archie behavior is attributable to the presence of conductive percolating grain-contact regions.

Introduction

Deviations from Archie’s law are known to occur, particularly at low water saturations, even for clean sandstones. It is unclear whether the deviations from Archie behavior observed at low pressures are also displayed at elevated pressures. In this paper, the authors present laboratory measurements of RI for two strongly water-wet sandstones at ambient and elevated pressures. The measurements are supplemented with high-resolution microcomputed-tomography (CT) imaging in dry and wet states at ambient pressure to determine an accurate description of the open resolved pore space and to attribute a finite porosity to fluid-saturated grain contacts at elevated pressure. Assuming that the main elements responding to effective stress are the grain contacts, grain-contact conductivities are estimated at elevated confining pressures with actual formation-­factor measurements for saturated samples at the same confining pressures. These are compared with computations on the ­micro-CT images. For Bentheimer, which contains image-resolvable clay regions, the clay regions are considered as additional conductive pathways with different stress dependence.

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 181484, “Experimental and Numerical Investigations on Stress Dependence of Sandstone Electrical Properties and Deviations From Archie’s Law,” by M.F. Farid, J.-Y. Arns, W.V. Pinczewski, and C.H. Arns, University of New South Wales, prepared for the 2016 SPE Annual Technical Conference and Exhibition, Dubai, 26–28 September. The paper has not been peer reviewed.
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Stress Dependence of Sandstone Electrical Properties and Deviations From Archie’s Law

01 August 2017

Volume: 69 | Issue: 8