Alkali Co-Solvent Polymer Flooding of High TAN Number Oil: Using Phase Experiments, Micro-Models and Corefloods for Injection Agent Selection

Abstract

Chemical Enhanced Oil Recovery leads to substantial incremental costs over waterflooding of oil reservoirs. Reservoirs containing oil with a high Total Acid Number (TAN) could be produced by injection of alkali. Alkali might lead to generation of soaps and emulsify the oil. However, the generated emulsions are not always stable. Phase experiments are used to determine the initial amount of emulsions generated and their stability if measured over time. Based on the phase experiments, the minimum concentration of alkali can be determined and the concentration of alkali above which no significant increase in formation of initial emulsions is observed. Micro-model experiments are performed to investigate the effects on pore scale. For injection of alkali into high TAN number oils, mobilization of residual oil after waterflooding is seen. The oil mobilization is due to breaking-up of oil ganglia or movement of elongated ganglia through the porous medium. As the oil is depleting in surface active components, residual oil saturation is left behind either as isolated ganglia or in down-gradient of grains. Simultaneous injection of alkali and polymers leads to higher incremental oil production in the micro-models owing to larger pressure drops over the oil ganglia and more effective mobilization accordingly. Core flood tests confirm the micro-model experiments and additional data are derived from these tests. Alkali co-solvent polymer injection leads to the highest incremental oil recovery of the chemical agents which is difficult to differentiate in micro-model experiments. The polymer adsorption is substantially reduced if alkali is injected with polymers compared with polymer injection only. The reason is the effect of the pH on the polymers. As in the micro-models, the incremental oil recovery is also higher for alkali polymer injection than with alkali injection only. To evaluate the incremental operating costs of the chemical agents, Equivalent Utility Factors (EqUF) are calculated. The EqUF takes the costs of the various chemicals into account. The lowest EqUF and hence lowest chemical incremental OPEX are incurred by injection of Na2CO3, however, the highest incremental recovery factor is seen with alkali co-solvent polymer injection. It should be noted that the incremental oil recovery owing to macroscopic sweep efficiency improvement by polymer needs to be taken into account to assess the efficiency of the chemical agents.

Wettability Changes Due to Nanomaterials and Alkali—A Proposed Formulation for EOR

“…The utilization of alkali leads to a drastic reduction of IFT as shown in Figure 3 b. As reported by Schumi et al [ 39 ] for the same oil, alkali reacts with the acidic components of the oil, producing in situ surfactants (soaps) which contribute mainly to the IFT reduction. An interesting behavior was a slight increase in the IFT at the beginning of the measurement, followed by a steep drop and stabilization—refer to Figure 3 b between the elapsed time of 0 and 80 min.…”

“…In previous work, we evaluated the nanomaterials alongside with alkali (Na 2 CO 3 ) and with polyacrylamide polymers as emulsion stabilizers [ 9 , 10 ]. This included the evaluation of possible effects of other nanoparticles, alkali, and polymer [ 9 , 10 ] or alkali polymer [ 38 , 39 ] on wettability, IFT, and phase behavior.…”

Micromodel Studies of Surfactant Flooding for Enhanced Oil Recovery: A Review

“…The further reduction of IFT to ultralow levels significantly improves the oil recovery . Under the ultralow IFT, the trapped oil ganglia become extremely flexible and flow as rivulets with injected surfactant solutions (Figure b). , Therefore, at favorable viscosity ratios, the ultralow IFT surfactant flooding can substantially improve oil recovery.…”