Improved Oil Recovery by Low Salinity Waterflooding: Surface Chemistry and SCAL Studies - Annual Report 2009.doc

Annual Report VISTA [2009]

Project Title: Improved Oil Recovery by Low Salinity Waterflooding: Surface Chemistry and SCAL Studies

Project director: Gisle Øye, Ugelstad Laboratory, Trondheim

PhD Scholar: Umer Farooq

Project Duration: 01-10-07 ------ 30-09-10

Technical Contact Person in Statoil: Medad T. Tweheyo

Divisional Head: Lars Høier

Project Number:

Objet:

The purpose of this project is to investigate the surface chemistry of typical reservoir surfaces where Low Salinity Waterflooding [LSW] can be used for improved oil recovery, and link this to SCAL studies. This combination will provide advanced understanding of the LSW mechanisms that will be useful when addressing the challenges encountered in flooding processes. The investigation of surface chemistry of reservoir surface will be divided into the following tasks: Task 1: To elucidate how variables such as pH, ion valency, ion concentration and temperature will affect the surface properties (potential distribution and contact angles) of selected model systems and reservoir samples using model brines as well as sea water. The zeta potentials will be determined, while direct titration experiments will be carried out in order to determine the surface potential. Task 2: To study the interaction of different crude oil components with model surfaces and the effect of salinity on desorption. Quartz Crystal Microbalance [QCM] will be used. Components from different fractions of crude oil will adsorb onto the reservoir surfaces. Adsorbed components will desorb with different concentrations of low saline water at different pHs. Task 3: Interfacial tension [IFT] measurements of different fractions of oil will be performed in different saline water and pHs. Contact angle measurements will also be performed on different model surfaces. Task 4: Zeta potential of different fractions of oil will be determined in different ionic solutions at different pHs and compare the studies with QCM and IFT results.

Status:

In order to fulfil the first task, potentiometric titrations and zeta potential measurements of model, outcrop and reservoir samples under low salinity, different cationic valency and pH ranges were performed. For all the minerals it was found that Ca2+ and Mg2+ reduced the electrophoretic mobility and zeta-potential more effectively than Na+ ions and the magnitude vary between ±20 mV. The presence of carbonates in outcrop and reservoir samples significantly affected the zeta-potential at high pH values by reversing the charge in divalent solutions. The compositional differences between the samples were also reflected in the point of zero charge (pzc) values. Samples containing more than 1.5% carbonates had point of zero charge in the range of pH 8-9, while samples with small fractions of carbonates or without carbonates had pzc values in the range of pH 2.9-3.3.

Desorption of asphaltenes from silica surface with low saline aqueous solutions of different ionic concentrations and valencies suggested that the 1500ppm of Na+ and 350ppm of Ca2+ desorb asphaltenes more effectively. Comparative adsorption/desorption studies of different fractions of crude oils suggested that high TBN [Total Base Number] crude oil or acid free fractions are relatively adsorbed more on silica crystals while high TAN [Total Acid Number] crude oil or base free fractions desorbed more effectively by different concentrations of low saline aqueous solutions.

Ionic valency and sequence of titration at different pH have significant influence on the zeta-potential values of different fractions of oil. Ca2+ and diluted sea water [1500ppm] shows profound interactions with different fractions of oil. Charge reversal effect is also observed at high pH values (pH > 8).

Base free crude oil at pH 9 in different Na+ solutions shows the minimum values (< 10 mN/m) of interfacial tension.

Publications:

1) Umer Farooq, Medad T. Tweheyo, Johan Sjöblom and Gisle Øye. “Surface Characterization of Model, Outcrop and Reservoir Samples in Low Salinity Aqueous Solutions” Accepted in Journal of Dispersion Science & Tech.

2) Umer Farooq, Medad T. Tweheyo, Johan Sjöblom and Gisle Øye. “Desorption Studies of Asphaltene from Silica Quartz Crystals Under Low Saline Aqueous Solutions” Manuscript is ready to publish

3) Umer Farooq, Medad T. Tweheyo, Johan Sjöblom and Gisle Øye. “Dynamic Interfacial Tension and Zeta Potential Measurements of Crude oil Fractions in High and Low Saline Aqueous Solutions” Writing Manuscript