Gas injection assisted steam huff-n-puff process for oil recovery from deep heavy oil reservoirs with low-permeability

Abstract

The primary objective of this paper is to evaluate the possibility of using gas assisted cyclic steam stimulation for enhanced oil recovery in Xinjiang low-permeability heavy oil reservoirs. Several attempts have been made in this paper to improve the recovery efficiency, which include hydraulic fracturing horizontal wells, flue-gas and CO2 assisted cyclic steam co-injection, alternating injection of steam and CO2 scheme.To reduce the heavy oil viscosity and heat losses, cyclic flue-gas/steam injection method was proposed to make the gas penetrate deep into the formation and expand the steam chamber. Numerical simulations were carried out to examine the thermal process recovery efficiency of gas assisted steam injection in producing low-permeability heavy oil.The numerical results indicated that gaseous additives such as CO2 or flue-gas were feasible to improve the performance of cyclic steam injection. Without a gas blanket filling the chamber, the heat losses would become significant. Our research results indicated that the CO2/steam coinjection yielded higher oil recovery than flue-gas/steam and pure cyclic steam injection process. The thermal recovery performance is largely dependent on the contacted area of the steam with the oil reservoir. One reason is that the cumulative injected enthalpy of the CO2/steam is higher than flue-gas/steam and pure steam. Another reason is that the addition of nitrogen or carbon dioxide acts a role as thermal isolation to reduce the heat losses along the wellbore due to their low conductivity. The interaction of CO2 injection with reservoir heavy oil under temperature effect was discussed. Compared with the case without considering the temperature effect, the oil rate and cumulative oil recovery was higher for the case including the temperature dependent relative permeability.