More than half of the global oil reserves are in carbonate reservoirs. Carbonate rocks, however, in most cases tend to be mixed-wet or oil-wet. Wettability alteration of carbonate reservoir rock has been proven to increase oil recovery significantly. Several chemicals have shown their effect on wettability; however, selection of an appropriate wettability modifier should be made on the basis of the underlying mechanisms and their behavior at reservoir conditions. This review discusses techniques that can help in assessing wettability alteration or reflect on the underlying mechanism and describes several categories of wettability modifiers focusing on their structure−property relationship and factors affecting their performance at reservoir conditions. Surfactants, nanoparticles, salts, and alkalis are four major categories of wettability modifiers that are discussed in this review. Among surfactants, gemini surfactants have great potential and could be a major focus of future research in this area. Nanoparticles are relatively novel materials for wettability alteration with the capability to reduce contact angle significantly at low cost. This review also identifies the current and future challenges related to the performance of various wettability modifiers at high-temperature and high-salinity conditions.

Alkyl thiols and alkenes (enes) polymerize via an extremely rapid step-growth, free-radical chain process, uninhibited by air, to give high-density networks with excellent mechanical and physical properties. These thiol-ene coatings are potentially useful for a wide variety of coatings, adhesives, and optical applications. In this work, a series of nanogold-containing UV-cured, thiol-ene coatings were prepared from trimethylolpropane tris(3-mercaptopropionate) (trithiol) and pentaerythritol allyl ether (triene) monomers using a unique procedure which facilitates precomplexation of the gold-thiol prior to photocuring. Irgacure 651 (1 wt %) was used as a photoinitiator, and nanogold was incorporated at 0-1 wt %, average ∼10 nm size particles by TEM. Physical and mechanical properties were characterized using bulk tack analysis and other standard techniques: DSC, TGA, pencil hardness, and gel fractions. In general, films were found to be low absorbing in the visible range and highly uniform and to contain well-dispersed nanogold particles. Although the rate of polymerization was modestly retarded by the presence of gold nanoparticles, functional group conversions (CdC and S-H) and gel fractions were high. Increasing nanogold content resulted in an increase in T g measured by DSC (-15 to -8 °C for 0-1 wt % nanogold, respectively) due to the increasing number of physical gold-thiol cross-links created. TGA analysis revealed a small negative impact of increasing nanogold composition on relative thermal stability. The 1 wt % nanogold-containing samples possessed appreciable electrostatic discharge (ESD) character, with ESD times of 1-10 s measured using a commercial charge plate analyzer.

No abstract

No abstract

No abstract

ABSTRACT:The adhesive properties, as measured by bulk tack and peel strength analysis, were found to decrease in polystyrene-block-polybutadiene-block-polystyrene (SBS) and polystyrene-block-polyisoprene-block-polystyrene (SIS) PSA films containing common singlet oxygen generators, acridine, rose bengal, and C 60 fullerene, when irradiated with a tungsten halogen light in air. The addition of the singlet oxygen quencher, b-carotene, to the C 60 fullerene samples was found to significantly deter the rate of adhesive loss in the fullerene-SBS and -SIS PSA nanocomposites. The presence of oxygen was essential to the mechanism of adhesive loss and, in combination with the effects of singlet oxygen generators and a singlet oxygen scavenger, strongly supports a singlet-oxygen mediated process. FTIR investigations of fullerene-SBS and -SIS systems suggest the initial formation of peroxides which, upon further irradiation, lead to the generation of carbonyl-containing compounds of a ketonic type after crosslinking. Rates of SBS and SIS C-H abstraction were comparable and found to decrease when the high-pressure, mercury xenon irradiation source was filtered to allow only light of k > 390 nm.

Gemini surfactants are novel surfactants that show unique properties, including low critical micelle concentrations, good water solubility, and outstanding performance in interfacial tension reduction. A previous study focusing on a group of locally synthesized cationic gemini surfactants found promising wettability alteration performance, which indicates the possible application in carbonate reservoirs that are naturally fractured and oil-wet. However, the tested surfactants seemed not to be efficient in high-salinity conditions. Chelating agents are used to reduce salinity by capturing the metal ions, helping maintain the performance of the selected enhanced oil recovery materials. In this study, wettability alteration by the locally synthesized ethoxylated quaternary ammonium gemini surfactant (GS8, with eight carbon atoms in the spacer group) alone and by the mixture between GS8 and a commonly used chelating agent [diethylenetriaminepentaacetic acid (DTPA)] was assessed by contact angle measurements. Results show that GS8 can modify strongly oil-wet Indiana limestone to intermediate-wet when dissolved in deionized water. Adding salts impairs the ability of the surfactant in altering wettability. The negative effect decreases in the sequence: CaCl2 > Na2SO4 > NaCl ≈ NaHCO3 ≈ MgCl2. The addition of DTPA improved the ability of the surfactant to alter the wettability in the presence of salts. A mixture of DTPA and GS8 showed better performance compared to GS8 and DTPA alone. These results suggested that, for high-salinity reservoirs, adding a chelating agent in combination with a cationic gemini surfactant could improve the wettability alteration.

No abstract