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Air injection into oil reservoirs for improved oil recovery is a proven technique in oilfields, while the safety of the process has been concerned over the possible explosion of natural gas at high pressure conditions. The combustion and explosion characteristics of natural gas-air mixture are also important for natural gas engines. In this study, ignited explosion experiments of methane-air mixtures have been conducted using a cylinder chamber under pressure up to 32 MPa, in which the influences of pressure on the explosion and flammability limits have been investigated. The experimental results indicate that the lower flammability limit of methane decreases slightly at elevated pressures, while its upper flammability limit increases significantly over 3 MPa, and the theoretical limiting oxygen concentration required for explosion is gradually reduced, posing greater explosion risks. At ambient temperature, the measured explosion limit range for methane in air is 2.93%–60.75%vol at 30 MPa, in contrast to 4.95% and 15.51%vol at atmospheric pressure, and the corresponding theoretical limiting oxygen concentration at 30 MPa can be reduced to as low as 5.86% from around 10% at 0.1 MPa when ignited using heated tungsten wire. A high pressure explosion limits model for methane-air mixture has been proposed based on the experimental data. • Ignited explosion experiments of methane at pressure up to 32 MPa was conducted. • The influences of pressure on the LFL, UFL and theoretical LOC was investigated. • A high pressure explosion limits model for methane-air mixtures was figured out. • The LFL of gases decreased with increasing the calorific values and combustion heat. • The pressure effect on the LFL could be attributed to the combustion heat. [ABSTRACT FROM AUTHOR]

CO 2 foam can be used for mobility control and blocking gas breakthrough channels during CO 2 injection for enhanced oil recovery, and specially designed and formulated foam agents are needed to enhance the stability of the foams especially under reservoir conditions. In this study, the performance of CO 2 foams with various surfactants has been investigated, including amide based surfactants (e.g. coconut monoethanol amide (CMEA), lauryl diethanol amide (LDEA)), amine based surfactants (cocoacyl propyl dimethylamine (UC 11 AMPM)), sodium dodecyl sulfate (SDS) and its mixtures with the amides and amines. A visualized high pressure and high temperature foam meter and a sand-pack flooding setup were used to assess the foam's performance, along with the surface tension measurement of the surfactant solutions in the presence of CO 2. The influence of temperature, the surface tension of the aqueous solution, and SDS on CO 2 foam performance of amide and amine based surfactant were investigated. The experimental results indicate that the amide or amine based surfactant alone all show poor foam performance, while their CO 2 foam stability and their mobility control capability can be greatly enhanced at high temperature up to 100 °C with the salinity of 50000 mg/L. After adding SDS to CMEA, LDEA, or UC 11 AMPM, an excellent synergistic effect can be formed among the molecules, which can reduce the surface tensions of individual surfactant solution and enhance the stability of CO 2 foams. • The CO 2 foam performance of amine and amide based surfactants were tested at HTHP conditions. • Stable CO 2 foams can be generated by amine surfactant with SDS at temperature up to 130 °C. • The synergistic effect of amine based surfactant with SDS has been demonstrated for CO 2 foams at high temperature. [ABSTRACT FROM AUTHOR]