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Experimental measurement of the exclusion-diffusion potential in sandstone and shaly sand samples at full and partial water saturation

Mutlaq Alarouj and Matthew David Jackson
Experimental measurement of the exclusion-diffusion potential in sandstone and shaly sand samples at full and partial water saturation
Geophysics (October 2022) 87 (5): M235-M246

Abstract

The exclusion-diffusion potential (EDP) arises in response to concentration gradients and is one of the key components of the self-potential (SP) observed in subsurface environments. However, few data are available to characterize the EDP in reservoir rocks saturated with complex natural brines and at partial brine saturation. We report experimental measurements of the EDP across fully and partially brine-saturated sandstone samples and fully brine-saturated shaly sand samples, using natural saline brine (2.2 Mol/L), seawater (0.5 Mol/L), and natural crude oil. When fully saturated, the EDP across the samples is diffusion-dominated, with the shaly samples exhibiting a small contribution from charge exclusion. The contribution of charge exclusion to the measured EDP increases as permeability decreases. At the residual oil saturation, the measured EDP is diffusion-dominated, consistent with our findings at full saturation. However, the EDP is more exclusive at the irreducible water saturation, and the polarity of the excluded ions depends on the polarity of the charged oil-brine interface. A charge exclusion is more significant at lower irreducible water saturation. Our results support recent studies suggesting that the oil-brine interface can be positively charged in contact with natural brines. The EDP trends reported have not been observed previously and have broad implications for geophysical monitoring of subsurface flow and transport, such as transport of nonaqueous phase contaminants in aquifers and water flow during hydrocarbon production.


ISSN: 0016-8033
EISSN: 1942-2156
Coden: GPYSA7
Serial Title: Geophysics
Serial Volume: 87
Serial Issue: 5
Title: Experimental measurement of the exclusion-diffusion potential in sandstone and shaly sand samples at full and partial water saturation
Affiliation: Imperial College London, Department of Earth Science and Engineering, London, United Kingdom
Pages: M235-M246
Published: 202210
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 40
Accession Number: 2023-001397
Categories: Applied geophysicsEconomic geology, geology of energy sources
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2023, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by Society of Exploration Geophysicists, Tulsa, OK, United States
Update Code: 202302
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