Despite the progress made on renewable energy, oil and gas remains the world's primary energy source. Meanwhile, large amounts of oil deposits remain unrecovered after application of traditional oil recovery methods. Chemical enhanced oil recovery (EOR) has been adjudged as an efficient oil recovery technique to recover bypassed oil and residual oil trapped in the reservoir. This EOR method relies on the injection of chemicals to boost oil recovery. In this overview, an up-to-date synopsis of chemical EOR with detailed explanation of the chemicals used, and the mechanism governing their oil recovery application have been discussed. Challenges encountered in the application of the various conventional chemical EOR methods were highlighted, and solutions to overcome the challenges were proffered. Besides, the recent trend of incorporating nanotechnology and their synergistic effects on conventional chemicals stability and efficiency for EOR were also explored and analysed. Finally, laboratory results and field projects were outlined. The review of experimental studies shows that porescale mechanisms of conventional chemical EOR is enhanced by incorporating nanotechnology, hence, resulted in higher efficiency. Moreover, the use of ionic liquid chemicals and novel alkaline-cosolvent-polymer technology shows good potentials. This overview presents an extensive information about chemical EOR applications for sustainable energy production.

This study investigated groundwater quality collected from two industrial and residential locations in each of Lagos metropolis. Prescribed standard procedures of American Public Health Association were used to measure physico-chemical parameters of each of the groundwater samples which include pH, EC, DO, TDS, BOD, COD, anions (Cl − , NO 3 − , SO 4 2− , PO 4 3− ) and heavy metals (Cu, Zn, Pb, Mn, Fe, Co, Cd and Cr). From laboratory analysis, measured physico-chemical parameters were within the permissible ranges specified by the WHO and NSDWQ except pH, TDS, EC, Pb, Mn and Fe for groundwater samples from industrial locations and pH, Pb, Mn and Fe for residential locations. Higher concentrations of TDS and EC reported for groundwater samples from industrial locations were attributed to heavy discharge of effluents from industrial treatment plants as well as dissolution of ionic heavy metals from industrial activities of heavy machines. Statistical Pearson's correlation revealed physico-chemical parameters of water quality to be moderately and strongly correlated with one another at either p < 0.05 or < 0.01.

This study is initiated to launch an activated carbon derived from Leucaena leucocephala seed pod as an adsorbent for the removal of hexavalent chromium from aqueous solution. The prepared activated carbon was characterized by proximate analysis, Brunauer-Emmett-Teller (BET) surface area measurement, scanning electron microscopic-energy dispersive Xray (SEM-EDX) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The effects of various variables, initial Cr(VI) concentration, contact time, adsorbent dosage, temperature and pH, which influence the adsorption process, were investigated. Equilibrium adsorption isotherms, kinetic and thermodynamic behaviour of the process were studied. The pH at point of zero charge (pH pzc) of 5.20 suggested that surface of the activated carbon was positively charged for pH below the pH pzc , attracting anions. The obtained results showed that 100 min contact time, 1.0 g adsorbent dose, 45 C temperature and solution pH of 6.0 resulted in maximum Cr(VI) uptake. The experimental data better fitted to the Langmuir isotherm with monolayer adsorption capacity of 26.94 mg/g. The kinetic analysis revealed that pseudo-second-order model fitted well to the acquired experimental data. The thermodynamic behaviour of Cr(VI) adsorption onto activated carbon was found to be spontaneous and endothermic in nature.

Polymers play a significant role in enhanced oil recovery (EOR) due to their viscoelastic properties and macromolecular structure. Herein, the mechanisms of the application of polymeric materials for enhanced oil recovery are elucidated. Subsequently, the polymer types used for EOR, namely synthetic polymers and natural polymers (biopolymers), and their properties are discussed. Moreover, the numerous applications for EOR such as polymer flooding, polymer foam flooding, alkali–polymer flooding, surfactant–polymer flooding, alkali–surfactant–polymer flooding, and polymeric nanofluid flooding are appraised and evaluated. Most of the polymers exhibit pseudoplastic behavior in the presence of shear forces. The biopolymers exhibit better salt tolerance and thermal stability but are susceptible to plugging and biodegradation. As for associative synthetic polyacrylamide, several complexities are involved in unlocking its full potential. Hence, hydrolyzed polyacrylamide remains the most coveted polymer for field application of polymer floods. Finally, alkali–surfactant–polymer flooding shows good efficiency at pilot and field scales, while a recently devised polymeric nanofluid shows good potential for field application of polymer flooding for EOR.

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