ORCID Profile
0000-0002-5081-0517
Current Organisations
Technical University of Denmark
,
Technical University of Denmark (DTU)
,
University of Nottingham
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Publisher: Society of Petroleum Engineers (SPE)
Date: 15-06-2016
DOI: 10.2118/169136-PA
Abstract: Core tests demonstrated that decreasing the salinity of injection water can increase oil recovery. Optimizing injection-water salinity, however, would offer a clear economic advantage for several reasons. Too-low salinity risks swelling of the clays that would lead to permanent reservoir damage, but evidence of effectiveness with moderate-salinity solutions would make it less difficult to dispose of produced water. The goal is to define boundary conditions so injection-water salinity is high enough to prevent reservoir damage and low enough to induce the low-salinity (LS) effect, while keeping costs and operational requirements at a minimum. Traditional core-plug testing for optimizing conditions has some limitations. Each test requires a fresh s le core-testing requires sophisticated and expensive equipment and reliable core-test data require several months because cores must be cleaned, restored, and aged before the tests can begin. It is also difficult to compare data from one core with results from another because no two cores are identical, making it difficult to distinguish between effects resulting from different conditions and effects resulting from different cores. Gathering statistics is limited by the time required for each test and the fact that core material is in short supply. Thus, our aim was to explore the possibility of a less-expensive, faster alternative by probing the fundamental chemical mechanisms behind the LS effect. We developed a method that uses atomic-force microscopy (AFM) to investigate the relationship between the wettability of pore surfaces and water salinity. We functionalize AFM tips with organic molecules and use them to represent tiny oil droplets of nonpolar molecules, and we use sand grains removed from core plugs to represent the pore walls in sandstone. We bring our “oil”-wet tip close to the sand-grain surface and measure the work of adhesion between the tip and the surface. Repeated probing of the surface with the tip produces data that one can convert to maps of adhesion, and we can estimate contact angle. Adhesion work is proportional to wettability and is directly correlated with the salinity of the fluid in contact with the tip and the particle surface. From our measurements, the threshold values for the onset of the LS response are 5,000 to 8,000 ppm, which benchmark remarkably well with observations from core-plug tests. From a mechanistic perspective, the correlation between salinity and adhesion provides evidence for the role of electrical-double-layer (EDL) expansion in the LS response expansion of the double layer decreases oil wettability. Because AFM experiments can be performed relatively quickly on very little material, they give the possibility of testing salinity response on many s les throughout a reservoir and for gathering statistics. Our approach provides a range of data that one can use to screen conditions to maximize the value of the core-plug testing and to provide extra data that would be too time consuming or too expensive to gather with traditional methods alone. Thus, AFM force mapping is an excellent complement to traditional core-plug testing.
Publisher: Elsevier BV
Date: 03-2014
Publisher: American Chemical Society (ACS)
Date: 14-07-2014
DOI: 10.1021/EF500218X
Publisher: American Chemical Society (ACS)
Date: 24-11-2014
DOI: 10.1021/LA5024967
Abstract: The interactions between mineral surfaces and organic molecules in water control many processes in nature and in the production of modern materials. To improve the understanding of fluid-surface interactions, we investigated the interface behavior of quartz and muscovite, a model for clay minerals, in aqueous solutions where the pH and composition were controlled. We used atomic force microscopy (AFM) in chemical force mapping (CFM) mode to measure adhesion using tips functionalized with alkyl, -CH3. By combining adhesion forces measured as a function of pH, with data from streaming potential experiments and DLVO calculations, we were able to determine the surface charge density. We observed increased adhesion between the mineral surface and the hydrophobic tips as the contact time increased from 7 ms to ∼2 s. The diffusion of dissolved ions takes time, and density functional theory (DFT) calculations did not indicate a strong hydration of the mineral surfaces. Therefore, we interpret that the loss of ions from the confined space between the tip and s le is a likely explanation of the correlation between the dwell time and adhesion. The maximum adhesion increase with dwell time for muscovite, i.e., 400 ± 77 pN, was considerably larger than for quartz, 84 ± 15 pN, which fits with the different surface structure and composition of the two minerals. We propose two mechanisms to explain these results: (1) cations that are structured in the solution and on the surface remain associated at the tip-s le interface initially but diffuse away during extended contact time and (2) adventitious carbon, the organic material that comes spontaneously from air and solution, can diffuse to the tip-s le interface during contact. This material decreases the surface energy by aggregating near the alkyl tip and increases adhesion between the tip and s le.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Nicolas Bovet.