Streaming potential and SP log in shaly sands

Abstract

The spontaneous potential in a well is controlled by the electrochemical phenomena in shaly sands and complicated by: (1) the bed thermodynamic conditions, (2) drilling mud chemistry, (3) the presence of a streaming potential, (4) bed water saturation, (5) bed lithological characteristics, etc. Therefore the spontaneous potential log is presently not a part of quantitative log analysis in shaly sands. Streaming potential phenomena within shaly sands are the subject of this paper. Theoretical assumptions, laboratory experiments and field tests confirmed that the streaming potential is controlled by: (1) streaming potential in the mud cake, (2) mud chemical composition, (3) bed and mud cake permeability, and (4) bed electrochemical activity. The temperature does not affect the streaming potential and the resulting conclusion is that the spontaneous potential reduction factor is affected very little by the streaming potential. The determination of formation water salinity requires additional information about the mud cake streaming potential. The results can be used for shaly sand SP-log interpretation.