The mounting evidence that waterflooding of clay-containing sandstone reservoirs using floodwater with reduced salinity can enhance oil recovery, but with unpredictably large variation in responses, demands improved understanding of the underlying mechanisms. Mobilization of clays and other fines is one candidate mechanism. Flow experiments in Berea sandstone plugs were designed such that the change in their fines distribution from before to after the oil and water injections could be imaged in exactly the same pores using scanning electron microscopy. This technique also allowed imaging of the wettability distribution on pore surfaces and was coupled to spectroscopic analysis of the adsorbed asphaltene amounts. One-phase flows switching from highto low-salinity water led to only a low level of fines mobilization, compared to two-phase experiments in which high-or low-salinity water displaced crude oil from mixed-wet prepared plugs. The images reveal that loosely bound, partially oil-wet fines lining sandstone grains are stripped by the adhering oil during its recovery and redeposited on grains further downstream. Reduced salinity increases the fraction of fines thus mobilized by weakening their bonds to grains and strengthening their bonds to oil. Evidence suggests that these more oil-wet fines stabilize the water-in-oil curved menisci, which can aid in maintaining the connectivity of the oil phase and thus enhance oil recovery.

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The microscopic wettability state of porous media, based on glass bead packings, after crude oil drainage of brine was investigated using X-ray micro-CT, white-light profilometry, and electron microscopy. Tomography revealed that the bulk residual brine occupied around 10% of void space, located in smaller pores and as pendular rings around bead contacts, in agreement with numerical simulations of drainage. The bead packing contained planar slabs of mica, quartz, and oxidized silicon wafer, which after flushing and disassembly of the pack allowed analysis of their wettability alteration due to deposition of asphaltenes from the crude oil. These substrates exhibited an overall pattern of rings with clean interiors, matching the brine pendular ring size inferred from experimental and simulated drainage, and asphaltene deposition in their exteriors, verifying the mixed wet model of oil reservoir wettability. The extent of asphaltene intrusion into ring interiors and completeness of asphaltene coverage of exteriors both increased with overall deposition tendency for the brine composition. The observed dependence on NaCl concentration and pH was consistent with expectations from DLVO and non-DLVO interactions governing brine thin film rupture and subsequent asphaltene deposition.

The two different approaches for the evaluation of molecular state electronic polarizabilities of ions based on Seitz–Ruffa (SR) energy level analysis and Wilson–Curtis–Coker model are critically analyzed by calculating the values of dipole moments within the framework of the original Rittner and the modified T-Rittner models. It is found that the polarizabilities based on SR energy level analysis along with the T-Rittner model are distinctly superior. These polarizabilities are used for determining spectroscopic constants for diatomic molecules of alkali halides and alkali hydrides. Various potential functions for the overlap repulsive energy proposed so far are used to estimate the binding energy and its various order derivatives. A comparison of calculated values with the experimental data shows that the modified Varshni–Shukla potential, among seven traditional potentials, and the Narayan–Ramaseshan (NR) potential, among three ion-dependent potentials, yield the best agreement with experimental data. Using these potentials we have calculated the values of spectroscopic constants viz. vibrational anharmonicity constant, rotational–vibrational coupling constant, and higher order spectroscopic constants. It is concluded that the results obtained by NR potential are distinctly superior to those obtained by the modified Varshni–Shukla potential function.

A number of useful thermodynamic approximations of wide applicability for describing high-pressure and high-temperature behaviour of solids are discussed with particular emphasis on the origin and equivalence of such approximations. Calculations of various thermodynamic quantities for NaCl crystals are performed and compared with available experimental data to demonstrate the usefulness of the approximations considered.