A novel in situ N2 generation system assisted by authigenic acid for formation energy enhancement in an oilfield

Abstract

The in situ N2 generation technique is a promising method for enhancing oil recovery (EOR) and blockage removal. Conventionally, N2 is generated through the redox reactions of sodium nitrite (NaNO2) and ammonium chloride (NH4Cl). The effect of several parameters on N2 production was studied in this work. The reaction kinetics between NaNO2 and NH4Cl were developed. The results revealed that the optimal molar ratio was 1 : 1 for the reactants and a higher concentration of reactants, H+ and higher temperature would lead to an increase in the gas production volume and a better gas-generating efficiency. The kinetic equation of the N2 generation reaction was defined as dc/dt = −7.103 × 107 cH+1.3291c02.0949e(−51.28 kJ mol−1)/RT. Methyl formate, ethyl formate, ammonium persulphate as well as paraformaldehyde were selected as authigenic acids by measuring their pH values and their effect on the rate of gas-generation, and the gas production volume was studied. An energy enhancement experiment was conducted to examine the influence of reactant concentration, initial pressure and different authigenic acids on energy enhancement and gas-generating efficiency. The results showed that the increase in reactant concentration can improve the energy enhancement while neither the reactant concentration nor the initial pressure could hardly influence the gas-generating efficiency. The presence of authigenic acids can considerably enhance both the gas production volume and the gas-generating efficiency of the system. The ammonium persulphate assisted N2 generation system is considered to be suitable for field applications.