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The production of sands in oil well production has long been a crucial and thorny issue, but many related technologies are either costly or ineffective. This study introduced a new aggregating reagent, pentaerythritol phosphate melamine salt (PPMS for short), for controlling this problem. PPMS was the reaction product of pentaerythritol, phosphoric acid, and melamine, and there was an amine and a phosphate ester (both are positively charged) in its chemical structure. It could effectively change the ζ potentials of solid particles and help them aggregate through hydrogen bonds and electrostatic interactions, thereby aggregated particles could settle down at the bottom of the pore holes without severe formation permeability damage, which plays a remarkable role in eliminating the co-production of formation particles with oil. PPMS exhibited an excellent performance when the concentration was 0.8 wt % under 60 °C at a neutral environment, at which PPMS (positively charged) not only can highly condense the double layer electric field but also can better react with clay particles (negatively charged) through adsorption and charge neutralization; thus the negative charge of clay surface could decrease to the minimum (almost 0 mV). At the same time, PPMS might have the potential to enhance oil recovery.

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A novel corrosion inhibitor, hexamethylenetetramine quaternary ammonium salt, is synthesized using hexamethylenetetramine (HMTA) and bromohexane as main reactants. The inhibitive action of HQAS on QT800-2 steel in hydrochloric acid medium is evaluated by weight-loss method, electrochemical method, and quantum chemical calculation. The obtained results show that the efficiency of 0.5 wt% HQAS inhibitor in 30 wt.% HCl solution at 363 K is 92.95% and HQAS can form an excellent synergistic effect with some additives. Polarization curves reveal that HQAS behaves as a mixed-type inhibitor with dominant anodic inhibition. Furthermore, the theoretical calculation verifies the relationship between the HQAS molecular structure and corrosion inhibition properties. K E Y W O R D Sacid inhibition, acid solutions, polarization, QT800-2 steel, quantum chemical calculation

Methane gas injected into reservoirs can greatly enhance oil recovery and has been widely used. However, continuous methane gas flooding has a deleterious effect on oil recovery enhancement and easily causes gas channeling in low-permeability heterogeneous reservoirs because of the low viscosity and high mobility of methane gas. This study consists of comprehensive experimental research that combines physical simulation and saturation dynamic monitoring technologies with a component analysis of produced oil to investigate the oil recovery and mobility control effects in lowpermeability heterogeneous cores. First, solubility, foaming ability, and stability are used as evaluation indicators. The results show that an alcohol ethoxylate foaming agent at 1.5 wt % is suitable for reservoirs, based on the Waring blender and Ross−Miles methods combined with microscopic observation. Second, methods of methane gas with water alternating gas (WAG) injection, advanced cyclic water alternating gas (ACWAG) injection, and methane nonionic foam injection are performed on three kinds of low-permeability heterogeneous cores under reservoir conditions. The experimental results show that methane nonionic foam flooding can significantly improve oil recovery by 11−18%. Third, the residual oil saturation in the core is tested by saturation dynamic monitoring. This finding indicates that methane nonionic foam flooding reduces mobility control, effectively restrains gas channeling, increases sweep efficiency, and has the highest permeability plugging rate (82−90%) for high-permeability channels. In the stage of methane WAG and ACWAG flooding, methane gas can increase the C 12 −C 24 components in the produced oil by 0.3−0.9%. ACWAG injection can improve the stage of no watercut oil recovery compared with conventional WAG injection.