A Surface Charge Approach to Investigating the Influence of Oil Contacting Clay Minerals on Wettability Alteration

Abstract A large percentage of petroleum reserves are located in carbonate reservoirs, which can be divided into limestone, chalk and dolomite. Roughly the oil recovery from carbonates is below the 30% due to the strong oil wetness, low permeability, abundance of natural fractures, and inhomogeneous rock properties Austad (2013). Injection of adjusted brine chemistry into carbonate reservoirs has been reported to increase oil recovery by 5-30% of the original oil in place in field tests and core flooding experiments. Previous studies have shown that adjusted waterflooding recovery in carbonate reservoirs is dependent on the composition and ionic strength of the injection brine (Morrow et al. 1998; Zhang 2005). Many research works have focused on the role of the brine composition in altering the initial wettability state of carbonate rock, which is usually intermediate- to oil-wet. Crude oils contain carboxyl group, -COOH, that can be found in the resin and asphaltenes fractions. The negatively charged carboxyl group, -COOH bond very strongly with the positively charged, sites on the carbonate surface. The carbonate surface, which is positively charged is believed to adsorb the SO42− that is negatively charged. On the other side cations Ca2+ and Mg2+ bind to the negatively charged carboxylic group and release it from the surface. In this study we use a closed system geochemical model to study the effect of the surface-charge dominant species; Ca2+, Mg2+ and SO42− on the carbonate surfaces at 80 °C. The proposed geochemical interactions can possibly lead to a change in the surface charge, altering wettability of the rock by exchanging ions/cations. Brines with various concentrations of Mg2+ and SO42− were prepared in the lab and contact angle between carbonate substrate and crude oil was measured using a rising/captive bubble tensiometer at 80 °C. The composition of the carbonate system was collected from previous literature review and the composition of adjusted brines was used to build a surface sorption database to develop a geochemical model. This model is focused on identifying the reaction paths and the surface behavior that may represent the real system. Changes in carbonate surface wettability were further evaluated using a series of contact angle experiments. Experimental observations and modeling results are concordant and imply that SO42− ions may alter the wettability of carbonate surface at high temperature.

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Effect of Chlorite Clay-Mineral Dissolution on the Improved Oil Recovery From Sandstone Rocks During Diethylenetriaminepentaacetic Acid Chelating-Agent Flooding

SPE Journal ◽

10.2118/189988-pa ◽

2018 ◽

Vol 23 (05) ◽

pp. 1880-1898 ◽

Cited By ~ 3

Author(s):

Mohamed Ahmed El-Din Mahmoud

Keyword(s):

Contact Angle ◽

Surface Charge ◽

Clay Minerals ◽

Oil Recovery ◽

Chelating Agent ◽

Oil Reservoirs ◽

Diethylenetriaminepentaacetic Acid ◽

Improved Oil Recovery ◽

Angle Measurements ◽

Contact Angle Measurements

Summary Sandstone oil reservoirs consist of different clay minerals, such as kaolinite, illite, and chlorite. While these clay minerals can highly affect oil recovery from sandstone oil reservoirs, no attention has been given to investigating the effects of clay minerals during such oil recovery, and no solution has been introduced to alleviate the effects. In this study, and for the first time, the effect of chlorite clay-mineral content on the improved oil recovery (IOR) from different sandstone rock samples was investigated. A new solution was proposed to eliminate the effect of chlorite on the oil recovery from sandstone rocks. Different sandstone cores were used, such as Berea (BSS), Bandera (BND), Kentucky (KSS), and Scioto (SCS) sandstone rocks with different clay minerals. ζ-potential measurements were used to investigate the surface charge of the different clays and different sandstone rocks with different fluids. Fluids such as seawater (SW), low-salinity water (LSW), fresh water, and chelating agents were used. Diethylenetriaminepentaacetic acid (DTPA) chelating agent was introduced to mitigate the chlorite effect on oil recovery from sandstone rocks. The wettability was evaluated using contact-angle measurements and the Amott test for different solutions and different rocks in the presence of actual crude oil. Coreflooding experiments were conducted using these fluids with different sandstone rocks to identify the effect of chlorite on the oil recovery. Coreflooding experiments showed that sandstone cores with high chlorite content yielded the lowest oil recovery when SW and LSW were used. The effect of chlorite on the oil recovery from the two sandstone rocks was minimized with 3 wt% DTPA chelating agent. More oil was recovered in the case of DTPA because of the iron chelation from chlorite. ζ-potential showed that sandstone with high chlorite content has a surface charge close to zero in the case of SW and fresh water. In addition, contact-angle measurements showed that samples with high chlorite content have less water-wetness, which will reduce oil recovery. Contact-angle measurements on chlorite sheets showed that chlorite is oil-wet compared with mica at the same conditions. The addition of high-pH DTPA chelating agent sequestered the iron from the chlorite clay minerals and changed the surface charge to very high negative value, and the contact angle confirmed that the rock changed to water-wet after adding the chelating agent. The Amott index showed that adding DTPA increased the water-wetness for SCS that contains 4 wt% chlorite.

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The role of clay minerals and the effect of H+ ions on removal of heavy metal (Pb2+) from contaminated soils

Canadian Geotechnical Journal ◽

10.1139/t99-106 ◽

2000 ◽

Vol 37 (2) ◽

pp. 296-307 ◽

Cited By ~ 31

Author(s):

Loretta Y Li ◽

Raymond S Li

Keyword(s):

Heavy Metals ◽

Heavy Metal ◽

Surface Charge ◽

Clay Minerals ◽

Contaminated Soils ◽

Surface Charges ◽

Buffer Solution ◽

Soil System ◽

Variable Charge ◽

Acid Leach

The importance of the surface charge of clay minerals (fixed or variable) and the effect of H+ ions on the adsorption and removal of Pb2+ ions from contaminated soil are investigated using kaolinite (variable charge) and two illitic (fixed charge) soils with pH 3.9 and 9.2. The adsorption-desorption characteristics of Pb2+ ions were determined using batch equilibrium tests and acid leach tests with various acids used to leach the soils. Under the same adsorption conditions, illitic soil adsorbed much more Pb2+ ions than kaolinite. The difference is largely due to the surface charges on the clay minerals. Removal of Pb2+ ions from variable-charge minerals (e.g., kaolinite) requires much less effort than removal of Pb2+ ions from constant-charge minerals (e.g., illite). The surface charge of a clay mineral has an important effect. By increasing the number of H+ ions available in the soil system with a buffer solution such as NaOAc-HOAc, heavy metals adsorbed on the clay surface are expelled to pore water. The increase in H+ ions in the soil system also assists in dissolving any metal carbonates, thereby increasing the solubility of heavy metals in illitic soil. The more H+ ions available in the pore fluid, the more Pb2+ ions can be released from the system.Key words: clay minerals, sorption, desorption, heavy metal, hydrogen ion, electrokinetic, acid leach.

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