50 results found
Vinogradov J, Hidayat M, Kumar Y, et al., 2022, Laboratory Measurements of Zeta Potential in Fractured Lewisian Gneiss: Implications for the Characterization of Flow in Fractured Crystalline Bedrock, APPLIED SCIENCES-BASEL, Vol: 12
Vinogradov J, Hidayat M, Sarmadivaleh M, et al., 2021, Predictive surface complexation model of the calcite-aqueous solution interface: The impact of high concentration and complex composition of brines, JOURNAL OF COLLOID AND INTERFACE SCIENCE, Vol: 609, Pages: 852-867, ISSN: 0021-9797
Hidayat M, Sarmadivaleh M, Derksen J, et al., 2021, Zeta potential of CO2-rich aqueous solutions in contact with intact sandstone sample at temperatures of 23 degrees C and 40 degrees C and pressures up to 10.0 MPa, JOURNAL OF COLLOID AND INTERFACE SCIENCE, Vol: 607, Pages: 1226-1238, ISSN: 0021-9797
Vinogradov J, Hill R, Jougnot D, 2021, Influence of Pore Size Distribution on the Electrokinetic Coupling Coefficient in Two-Phase Flow Conditions, WATER, Vol: 13
Martyushev DA, Vinogradov J, 2021, Development and application of a double action acidic emulsion for improved oil well performance: laboratory tests and field trials, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, Vol: 612, ISSN: 0927-7757
Udoh T, Vinogradov J, 2021, Controlled Salinity-Biosurfactant Enhanced Oil Recovery at Ambient and Reservoir Temperatures-An Experimental Study, ENERGIES, Vol: 14
Kumar Y, Comte J, Vinogradov J, et al., 2021, Mapping fracture flow anisotropy using the Self Potential method: field and laboratory experiments
Recent studies have shown the potential of SP to identify and quantify groundwater flow in fractured rocks, including hydraulically active fractures, fracture connectivity, and preferential flow directions. The presented work reports combined laboratory and field SP experiments applied to a fractured gneissic aquifer system in NW Scotland characterised by the occurrence of several fracture sets and a major regional-scale fault zone. Field surveys involved both SP transects and azimuthal SP surveys and revealed clear anomalies including anisotropy that matched the dominant fracture set directions, for both local scale fracture sets and the regional fault zone, which were previously mapped from outcrop observations and electrical resistivity tomography. Collected fractured gneiss samples were analysed in the laboratory and provided values for the electrokinetic coupling coefficient and zeta potential which were further used to quantitatively interpret field SP data in terms of groundwater pressure gradients. Results showed that groundwater pressure gradients were notably higher along one of the dominant fracture set than along the other near-orthogonal one, which coincides with the fault zone. These results confirm the hydrogeological conceptual model in which the fault zone would act as a high permeability/high flow rate drain for the surrounding, less fractured rock mass.
Jougnot D, Thanh LD, Soldi M, et al., 2021, Predicting streaming potentials in partially saturated porous media, a review of capillary-based models
In the last two decades, geophysical methods are emerging to characterize and monitor hydrosystems in the critical zone. The vadose zone is the compartment of the near surface where the pore space is saturated both by water and air, this yields a very complex and nonlinear behavior in terms of water distribution and dynamics. The combination of electrical resistivity imaging and streaming potential have shown their potential to study this compartment. The streaming potential is particularly interesting as it is directly linked to the water flow and therefore offers a way for in situ monitoring. Nevertheless, the use of appropriate petrophysical relationships is required to quantitatively relate the streaming potential signals to the water flow, i.e., to model the electrokinetic coupling phenomena. During the last decade, the development of capillary-based models opened large perspectives to model flow, transport, and coupling in partially saturated porous media. In this contribution, we propose a critical comparison of existing electrokinetic coupling models, from the up-scaling approach they are based on to the capillary size distribution they consider to explain the streaming potential signal, or the shape of the capillaries they consider to explain complex features such as hysteresis.
MacAllister DJ, Graham MT, Vinogradov J, et al., 2019, Characterising the self-potential response to concentration gradients in heterogeneous sub-surface environments, Journal of Geophysical Research. Solid Earth, Vol: 124, Pages: 7918-7933, ISSN: 2169-9356
Self‐potential (SP) measurements can be used to characterise and monitor, in real‐time, fluid movement and behaviour in the sub‐surface. The electrochemical exclusion‐diffusion (EED) potential, one component of SP, arises when concentration gradients exist in porous media. Such concentration gradients are of concern in coastal and contaminated aquifers, and oil and gas reservoirs. It is essential that estimates of EED potential are made prior to conducting SP investigations in complex environments with heterogeneous geology and salinity contrasts, such as the UK Chalk coastal aquifer. Here, we report repeatable laboratory estimates of the EED potential of chalk and marls using natural groundwater (GW), seawater (SW), deionised (DI) water and 5 M NaCl. In all cases the EED potential of chalk was positive (using a GW/SW concentration gradient the EED potential was c.14 to 22 mV), with an increased deviation from the diffusion limit at the higher salinity contrast. Despite the relatively small pore size of chalk (c.1 μm), it is dominated by the diffusion potential and has a low exclusion‐efficiency, even at large salinity contrasts. Marl samples have a higher exclusion‐efficiency which is of sufficient magnitude to reverse the polarity of the EED potential (using a GW/SW concentration gradient the EED potential was c.‐7 to ‐12 mV) with respect to the chalk samples. Despite the complexity of the natural samples used, the method produced repeatable results. We also show that first order estimates of the exclusion‐efficiency can be made using SP logs, supporting the parameterisation of the model reported in Graham et al. (2018), and that derived values for marls are consistent with the laboratory experiments, while values derived for hardgrounds based on field data indicate a similarly high exclusion‐efficiency. While this method shows promise in the absence of laboratory measurements, more rigorous estimates should be made where possible and can be conducted following
Udoh T, Vinogradov J, 2019, Experimental Investigations of Behaviour of Biosurfactants in Brine Solutions Relevant to Hydrocarbon Reservoirs, COLLOIDS AND INTERFACES, Vol: 3, ISSN: 2504-5377
Udoh T, Vinogradov J, 2019, Effects of temperature on crude-oil-rock-brine interactions during controlled salinity biosurfactant flooding
The effect of temperature and brine composition on Crude-Oil-Rock-Brine (CORB) interactions during controlled salinity brine and biosurfactant injection process were investigated and reported in this study. Comprehensive core flooding experiments were carried out using formation brine, controlled salinity brine and combined controlled salinity biosurfactant brine injection in carbonate core samples at 23 °C and 70 °C. Effluent analyses and oil recovery from each flooding experiment were used to interpret the temperature and brine composition effect on the CORB interactions. The results of this study show that increased temperature makes no significant impact on CORB interactions during high salinity brine flooding. Increased temperature however, enhances CORB interactions through increased reactivity during controlled salinity brine and controlled salinity biosurfactant brine flooding thereby, resulting in increased oil production. Furthermore, the results of this study demonstrated the enhanced oil recovery potential of combined controlled salinity brine and biosurfactant application in condition relevant to hydrocarbon reservoirs.
Udoh T, Vinogradov J, 2019, A Synergy between Controlled Salinity Brine and Biosurfactant Flooding for Improved Oil Recovery: An Experimental Investigation Based on Zeta Potential and Interfacial Tension Measurements, INTERNATIONAL JOURNAL OF GEOPHYSICS, Vol: 2019, ISSN: 1687-885X
Vinogradov J, Jackson MD, Chamerois M, 2018, Zeta potential in sandpacks: Effect of temperature, electrolyte pH, ionic strength and divalent cations, Colloids and Surfaces A: Physicochemical and Engineering Aspects, Vol: 553, Pages: 259-271, ISSN: 0927-7757
Rocks in many subsurface settings are at elevated temperature and are saturated with brines of high ionic strength (high salinity) containing divalent ions. Yet most laboratory measurements of zeta potential in earth materials are obtained at room temperature using simple monovalent electrolytes at low ionic strength. Consequently, the zeta potential at conditions relevant to many subsurface settings is not known. We report experimental measurements of the temperature dependence of the zeta potential in well characterised, natural quartz sandpacks over the temperature range 23–120 °C saturated with electrolytes containing divalent ions at a range of concentrations relevant to natural systems. We find that the key control on zeta potential in these unbuffered experiments is pH, which varies in response to temperature and electrolyte composition. The zeta potential is negative irrespective of sample or electrolyte, but its magnitude is strongly correlated to pH, which varies both with temperature and the concentration of divalent ions. The pH decreases with increasing temperature at low ionic strength, but is independent of temperature at high ionic strength. The pH is also typically lower in the presence of divalent ions, irrespective of the total ionic strength. The zeta potential increases in magnitude with increasing pH. Different relationships between zeta potential, temperature and concentration of divalent ions could be obtained in buffered experiments where the pH is fixed at a given value.
Malcolm G, Jackson M, MacAllister DJ, et al., 2018, Self-potential as a predictor of seawater intrusion in coastal groundwater boreholes, Water Resources Research, Vol: 54, Pages: 6055-6071, ISSN: 0043-1397
Monitoring of self‐potentials (SP) in the Chalk of England has shown that a consistent electrical potential gradient exists within a coastal groundwater borehole previously affected by seawater intrusion (SI) and that this gradient is absent in boreholes further inland. Furthermore, a small but characteristic reduction in this gradient was observed several days prior to SI occurring. We present results from a combined hydrodynamic and electrodynamic model, which matches the observed phenomena for the first time and sheds light on the source mechanisms for the spatial and temporal distribution of SP. The model predictions are highly sensitive to the relative contribution of electrochemical exclusion and diffusion potentials, the ‘exclusion efficiency’, in different rock strata. Geoelectric heterogeneity, largely due to marls and hardgrounds with a relatively high exclusion efficiency, was the key factor in controlling the magnitude of the modelled SP gradient ahead of the saline front and its evolution prior to breakthrough. The model results suggest that, where sufficient geoelectric heterogeneity exists, borehole SP may be used as an early warning mechanism for SI.
MacAllister DJ, Jackson MD, Butler AP, et al., 2018, Remote detection of saline intrusion in a coastal aquifer using borehole measurements of self potential, Water Resources Research, Vol: 54, Pages: 1669-1687, ISSN: 0043-1397
Two years of self‐potential (SP) measurements were made in a monitoring borehole in the coastal UK Chalk aquifer. The borehole SP data showed a persistent gradient with depth, and temporal variations with a tidal power spectrum consistent with ocean tides. No gradient with depth was observed at a second coastal monitoring borehole ca. 1 km further inland, and no gradient or tidal power spectrum were observed at an inland site ca. 80 km from the coast. Numerical modeling suggests that the SP gradient recorded in the coastal monitoring borehole is dominated by the exclusion‐diffusion potential, which arises from the concentration gradient across a saline front in close proximity to, but not intersecting, the base of the borehole. No such saline front is present at the two other monitoring sites. Modeling further suggests that the ocean tidal SP response in the borehole, measured prior to breakthrough of saline water, is dominated by the exclusion‐diffusion potential across the saline front, and that the SP fluctuations are due to the tidal movement of the remote front. The electrokinetic potential, caused by changes in hydraulic head across the tide, is one order of magnitude too small to explain the observed SP data. The results suggest that in coastal aquifers, the exclusion‐diffusion potential plays a dominant role in borehole SP when a saline front is nearby. The SP gradient with depth indicates the close proximity of the saline front to the borehole and changes in SP at the borehole reflect changes in the location of the saline front. Thus, SP monitoring can be used to facilitate more proactive management of abstraction and saline intrusion in coastal aquifers.
Jackson MD, Li S, Al Mahrouqi D, et al., 2018, Measurements of zeta potential in intact carbonate samples with application to controlled salinity waterflooding
© 2018 Society of Petroleum Engineers. All rights reserved. Laboratory experiments and field trials have shown that oil recovery from carbonate reservoirs can be increased by modifying the brine composition injected during recovery in a process termed controlled salinity water-flooding (CSW). However, CSW remains poorly understood and there is no method to predict the optimum CSW composition. This work demonstrates that improved oil recovery (IOR) during CSW is strongly correlated to changes in zeta potential at both the mineral-brine and oil-brine interfaces. We report experiments in which IOR during CSW occurs only when the change in brine composition induces a repulsive electrostatic force between these interfaces. The polarity of the zeta potential at both interfaces must be determined when designing the optimum CSW composition. Results show that the zeta potential at the oil-water interface may be positive at conditions relevant to carbonate reservoirs and this has a significant impact on the choice of optimum bring composition for CSW. We report new measurements of zeta potential in intact carbonates at reservoir conditions of temperature and brine composition to understand how the zeta potential changes during CSW.
Udoh T, Akanji L, Vinogradov J, 2018, Experimental investigation of potential of combined controlled salinity and bio-surfactant CSBs in enhanced oil recovery EOR processes
In this study, we investigate potential application of environment-friendly bio-surfactants (EFBS) in EOR processes. We assess the prospect of combining the EFBS with controlled salinity (CS) water injection in optimising oil recovery using rhamnolipid and protein-enzyme as case study. Rock component analysis, bio-surfactant solubility in brine of varied concentration and composition, crude oil-brine interfacial tension (IFT) and bio-surfactants emulsification activity test were carried out as part of the preliminary investigations. Following these preliminary analyses, a series of comprehensive core flooding displacement experiments were used to investigate the EOR potential of CSBS injection process. Finally, effluent analyses were conducted to study the effect of this combined process on dynamic oil-brine-rock interactions. Results of the IFT tests using 0.0083-3M brine concentrations show IFT reduction from 3.40-2.5 mN/m with increasing salinity for protein-enzyme while increase in IFT from 0.11-0.34mN/m was observed with increasing salinity for rhamnolipid. However, using a fixed brine concentration of 8.3mM with varied biosurfactant concentration, IFT reduction with increase in concentration was observed for both of them. Also, the two bio-surfactants exhibited stable emulsion active in varied brine salinity investigated. Protein-enzyme is soluble in varied brine formulation while rhamnolipid solubility was found to be dependent on the brine composition and system pH rather than the ionic strength. Furthermore, from the secondary injection of CS and CSBS, the highest recovery factor of 82.76% was achieved with CSBS (protein-enzyme). However, in the tertiary applications, the highest recovery of 83.40% was achieved in the CS injection. Finally, increased pH, Ca2+ and Mg2+ concentrations was observed with both CS and CSBS flooding. This suggests reaction between excess cations and previously adsorbed carboxylic group of crude-oil led to increased recovery. Where
Jackson MD, Li S, Al Mahrouqi D, et al., 2018, Measurements of zeta potential in intact carbonate samples with application to controlled salinity waterflooding
Laboratory experiments and field trials have shown that oil recovery from carbonate reservoirs can be increased by modifying the brine composition injected during recovery in a process termed controlled salinity water-flooding (CSW). However, CSW remains poorly understood and there is no method to predict the optimum CSW composition. This work demonstrates that improved oil recovery (IOR) during CSW is strongly correlated to changes in zeta potential at both the mineral-brine and oil-brine interfaces. We report experiments in which IOR during CSW occurs only when the change in brine composition induces a repulsive electrostatic force between these interfaces. The polarity of the zeta potential at both interfaces must be determined when designing the optimum CSW composition. Results show that the zeta potential at the oil-water interface may be positive at conditions relevant to carbonate reservoirs and this has a significant impact on the choice of optimum bring composition for CSW. We report new measurements of zeta potential in intact carbonates at reservoir conditions of temperature and brine composition to understand how the zeta potential changes during CSW.
Zhang J, Vinogradov J, Leinov E, et al., 2017, Streaming potential during drainage and imbibition, JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, Vol: 122, Pages: 4413-4435, ISSN: 2169-9313
Al Mahrouqi D, Vinogradov J, Jackson MD, 2016, Zeta potential of artificial and natural calcite in aqueous solution, Advances in Colloid and Interface Science, Vol: 240, Pages: 60-76, ISSN: 0001-8686
Despite the broad range of interest and applications, controls on calcite surface charge in aqueous solution, especiallyat conditions relevant to natural systems, remain poorly understood. The primary data source to understandcalcite surface charge comprises measurements of zeta potential. Here we collate and review previousmeasurements of zeta potential on natural and artificial calcite and carbonate as a resource for future studies,compare and contrast the results of these studies to determine key controls on zeta potential and where uncertaintiesremain, and report new measurements of zeta potential relevant to natural subsurface systems.The results show that the potential determining ions (PDIs) for the carbonate mineral surface are the lattice ionsCa2+, Mg2+ and CO32−. The zeta potential is controlled by the concentration-dependent adsorption of these ionswithin the Stern layer, primarily at the Outer Helmholtz Plane (OHP). Given this, the Iso-Electric Point (IEP) atwhich the zeta potential is zero should be expressed as pCa (or pMg). It should not be reported as pH, similarto most metal oxides.The pH does not directly control the zeta potential. Varying the pH whilst holding pCa constant yields constantzeta potential. The pH affects the zeta potential only by moderating the equilibrium pCa for a given CO2 partialpressure (pCO2). Experimental studies that appear to yield a systematic relationship between pH and zeta potentialare most likely observing the relationship between pCa and zeta potential, with pCa responding to the changein pH. New data presented here show a consistent linear relationship between equilibrium pH and equilibriumpCa or pMg irrespective of sample used or solution ionic strength. The surface charge of calcite is weakly dependenton pH, through protonation and deprotonation reactions that occur within a hydrolysis layer immediatelyadjacent to the mineral surface. The Point of Zero Charge (PZC) at which the surface charge is zero could b
Al Mahrouqi D, Vinogradov J, Jackson MD, 2016, Zeta potential of artificial and natural calcite in aqueous solution., Adv Colloid Interface Sci, Vol: 240, Pages: 60-76
Despite the broad range of interest and applications, controls on calcite surface charge in aqueous solution, especially at conditions relevant to natural systems, remain poorly understood. The primary data source to understand calcite surface charge comprises measurements of zeta potential. Here we collate and review previous measurements of zeta potential on natural and artificial calcite and carbonate as a resource for future studies, compare and contrast the results of these studies to determine key controls on zeta potential and where uncertainties remain, and report new measurements of zeta potential relevant to natural subsurface systems. The results show that the potential determining ions (PDIs) for the carbonate mineral surface are the lattice ions Ca(2+), Mg(2+) and CO3(2-). The zeta potential is controlled by the concentration-dependent adsorption of these ions within the Stern layer, primarily at the Outer Helmholtz Plane (OHP). Given this, the Iso-Electric Point (IEP) at which the zeta potential is zero should be expressed as pCa (or pMg). It should not be reported as pH, similar to most metal oxides. The pH does not directly control the zeta potential. Varying the pH whilst holding pCa constant yields constant zeta potential. The pH affects the zeta potential only by moderating the equilibrium pCa for a given CO2 partial pressure (pCO2). Experimental studies that appear to yield a systematic relationship between pH and zeta potential are most likely observing the relationship between pCa and zeta potential, with pCa responding to the change in pH. New data presented here show a consistent linear relationship between equilibrium pH and equilibrium pCa or pMg irrespective of sample used or solution ionic strength. The surface charge of calcite is weakly dependent on pH, through protonation and deprotonation reactions that occur within a hydrolysis layer immediately adjacent to the mineral surface. The Point of Zero Charge (PZC) at which the surface char
Long-term surface and borehole self-potential (SP) monitoring was conducted in the UK Chalk aquifer at two sites. The coastal site is ~1.7 km from the coast, and the inland site is ~80 km from the coast. At both sites, power spectral density analysis revealed that SP data contain the main ocean tidal periodic components. However, the principal lunar component (M2), the dominant ocean tidal component, was most significant at the coastal site. The M2 signal in surface-referenced SP data at the inland site was partly due to telluric currents caused by the geomagnetic ocean dynamo. Earth and/or atmospheric tides also contributed, as the SP power spectrum was not typical of a telluric electric field. The M2 component in borehole-referenced data at the inland site was below the significance level of the analysis method and was 2 orders of magnitude smaller than the M2 signal in borehole-referenced SP data at the coastal site. The tidal response of the SP data in the coastal borehole is, therefore, primarily driven by ocean tides. These cause changes in fluid pressure and chemical concentration gradients within the coastal aquifer, leading to time varying electrokinetic and exclusion-diffusion potentials. Borehole-referenced SP measurements could be used to characterize and monitor tidal processes in coastal aquifers such as the intrusion of seawater.
Jackson MD, Al-Mahrouqi D, Vinogradov J, 2016, Zeta potential in oil-water-carbonate systems and its impact on oil recovery during controlled salinity water-flooding, Scientific Reports, Vol: 6, ISSN: 2045-2322
Laboratory experiments and field trials have shown that oil recovery from carbonate reservoirs can be increased by modifying the brine composition injected during recovery in a process termed controlled salinity water-flooding (CSW). However, CSW remains poorly understood and there is no method to predict the optimum CSW composition. This work demonstrates for the first time that improved oil recovery (IOR) during CSW is strongly correlated to changes in zeta potential at both the mineral-water and oil-water interfaces. We report experiments in which IOR during CSW occurs only when the change in brine composition induces a repulsive electrostatic force between the oil-brine and mineral-brine interfaces. The polarity of the zeta potential at both interfaces must be determined when designing the optimum CSW composition. A new experimental method is presented that allows this. Results also show for the first time that the zeta potential at the oil-water interface may be positive at conditions relevant to carbonate reservoirs. A key challenge for any model of CSW is to explain why IOR is not always observed. Here we suggest that failures using the conventional (dilution) approach to CSW may have been caused by a positively charged oil-water interface that had not been identified.
Al-Mahrouqi, Vinogradov J, Jackson MD, 2016, Temperature-dependence of the zeta potential in intact natural carbonates, Geophysical Research Letters, Vol: 43, Pages: 11578-11587, ISSN: 1944-8007
The zeta potential is a measure of the electrical charge on mineral surfaces and is an important control on subsurface geophysical monitoring, adsorption of polar species in aquifers, and rock wettability. We report the first measurements of zeta potential in intact, water-saturated, natural carbonate samples at temperatures up to 120°C. The zeta potential is negative and decreases in magnitude with increasing temperature at low ionic strength (0.01 M NaCl, comparable to potable water) but is independent of temperature at high ionic strength (0.5 M NaCl, comparable to seawater). The equilibrium calcium concentration resulting from carbonate dissolution also increases with increasing temperature at low ionic strength but is independent of temperature at high ionic strength. The temperature dependence of the zeta potential is correlated with the temperature dependence of the equilibrium calcium concentration and shows a Nernstian linear relationship. Our findings are applicable to many subsurface carbonate rocks at elevated temperature.
Jackson MD, Vinogradov J, Hamon G, et al., 2016, Evidence, mechanisms and improved understanding of controlled salinity waterflooding part 1: Sandstones, FUEL, Vol: 185, Pages: 772-793, ISSN: 0016-2361
Alroudhan A, Vinogradov J, Jackson MD, 2016, Zeta potential of intact natural limestone: Impact of potential-determining ions Ca, Mg and SO4, Colloids and Surfaces A - Physicochemical and Engineering Aspects, Vol: 493, Pages: 83-98, ISSN: 0927-7757
We report measurements of the zeta potential on intact limestone samples obtained using the streaming potential method (SPM), supplemented by the more ubiquitous electrophoretic mobility method (EPM). The effect of the potential-determining ions (PDI) Ca, Mg and SO4, and the total ionic strength controlled by NaCl concentration, is investigated over the range typical of natural brines. We find that the zeta potential varies identically and linearly with calcium and magnesium concentration expressed as pCa or pMg. The zeta potential also varies linearly with pSO4. The sensitivity of the zeta potential to PDI concentration, and the IEP expressed as pCa or pMg, both decrease with increasing NaCl concentration. We report considerably lower values of IEP than most previous studies, and the first observed IEP expressed as pMg. The sensitivity of the zeta potential to PDI concentration is lower when measured using the SPM compared to the EPM, owing to the differing location of the shear plane at which the zeta potential is defined. SPM measurements are more appropriate in natural porous samples because they reflect the mineral surfaces that predominantly interact with the adjacent fluids. We demonstrate that special cleaning procedures are required to return samples to a pristine zeta potential after exposure to PDIs. We apply our results to an engineering process: the use of modified injection brine composition to increase oil recovery from carbonate reservoirs. We find a correlation between an increasingly negative zeta potential and increased oil recovery.
Al Mahrouqi DA, Vinogradov J, Jackson MD, 2016, Optimization of controlled salinity waterflooding in carbonates
The impact of brine composition on rock wettability and oil recovery in carbonates has been an area of research in recent years. Many studies have reported contradictory results concerning the impact of water injection salinity and composition on oil recovery. The zeta potential, which is a measure of the electrical charge at the mineral surface, is highly variable in carbonates, depending on the ionic composition of the pore water. The zeta potential controls the magnitude and polarity of the electrostatic interactions between the mineral surface and polar species in the brine and oil; it also controls the magnitude and polarity of the streaming potential, an electrical potential which arises in response to pressure gradients across saturated rocks. Here we report the use of streaming potential measurements to characterize wettability and optimize injection brine composition during controlled salinity waterflooding (CSW) in carbonates. Crude oils, natural carbonate core samples and synthetic brines (equivalent to formation, seawater and modified seawater compositions) are used to evaluate wettability and CSW effect. We use the streaming potential measurements to determine the zeta potential, and correlate changes in zeta potential with changes in wettability and improved oil recovery. To predict the optimum brine composition for CSW requires knowledge of the zeta potential and how this responds to changes in brine composition. Such knowledge can be obtained using the streaming potential method reported here, which is much cheaper and quicker than conducting numerous multiphase coreflooding experiments and varying the brine composition on an ad-hoc basis.
Vinogradov J, Jackson MD, 2015, Zeta potential in intact natural sandstones at elevated temperatures, Geophysical Research Letters, Vol: 42, Pages: 6287-6294, ISSN: 1944-8007
We report measurements of the zeta potential of natural sandstones saturated with NaCl electrolytes of varying ionic strengths at temperatures up to 150°C. The zeta potential is always negative but decreases in magnitude with increasing temperature at low ionic strength (0.01 M) and is independent of temperature at high ionic strength (0.5 M). The pH also decreases with increasing temperature at low ionic strength but remains constant at high ionic strength. The temperature dependence of the zeta potential can be explained by the temperature dependence of the pH. Our findings are consistent with published models of the zeta potential, so long as the temperature dependence of the pH at low ionic strength is accounted for and can explain the hitherto contradictory results reported in previous studies.
Vinogradov J, Jackson MD, 2015, Zeta potential in intact natural sandstones at elevated temperatures, Geophysical Research Letters, ISSN: 1944-8007
Jackson M, Vinogradov J, 2013, Permanent reservoir monitoring using passive electrical measurements
Downhole monitoring of the spontaneous electrical potential (SP), using electrodes permanently installed on production or injection wells, is a promising new technology for imaging waterfronts and monitoring water movement in a hydrocarbon reservoir, in real time, during production. The method is distinct from other electrical methods because these require an active source and are limited in their depth of investigation. The SP signal is generated by moving water, salinity and temperature fronts in the reservoir, allowing a (much) greater depth of investigation and requiring less sophisticated downhole hardware. This presentation will review the results of numerical modelling and laboratory experimentation that suggests waterfronts can be monitored while they are several tens to hundreds of metres away from an instrumented well. Other potential applications, and the next steps required to implement the method as a viable technology, are also discussed.
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