Sweep enhancers for oil recovery

The use of viscoelastic sweep improvers to overcome injected fluid diversion is assessed at the low pressure gradients associated with secondary oil production. The flow evolves from Newtonian to non-Newtonian behavior with increasing pressure gradient. Additive concentration determines this transition and controls the effectiveness of selective retardation. This is demonstrated in an experimental simulation of parallel flow in two core samples of different permeabilities. Even at pressure gradients lower than 1.0 bar/m channeling can effectively be reduced and early water breakthrough delayed. This has the potential to greatly increase ultimate oil recovery

Viscoelastic surfactants for diversion control in oil recovery

Hydrocarbon recovery is significantly improved in heterogeneous systems by injecting viscoelastic surfactant solutions. These solutions retard the effect of preferential flow through so called ‘thief zones’ (high permeability regions). The viscoelastic fluid passively increases flow resistance in regions of high permeability thereby partially blocking thief-zones. The low permeability volume paths in these heterogeneous reservoirs are swept more efficiently since less of the injected flooding fluid is lost. The produced water cut is significantly reduced which increases the overall effectiveness of the recovery process. The solutions we used are self-regulating, making them universally applicable without extensive knowledge of the reservoir properties

Improved oil reservoir sweep with viscoelastic surfactants

Viscoelastic surfactant solutions increase oil recovery by selectively modifying the viscosity of the injected displacing fluid in different zones of the reservoir. We demonstrate that flow resistance in high permeability zones is increased whereas no significant change in viscosity occurs in low permeability zones. This greatly reduces injected fluid losses via the high permeability route. In two phase flow in sandstones, recovery increases by about 25%. Efficiency also increases by a factor of 3 as shown by the large reduction in injected volume at breakthrough. Consequently less fluid is lost through high permeability thief zones. Recovery is increased in carbonates as well but the efficiency is depleted due to apparent changes in wetting. The reduction in injected fluid before breakthrough has the potential to prolong the economical lifespan of water wet reservoirs

Flow of viscoelastic surfactants through porous media

We compare the flow behavior of viscoelastic surfactant (VES) solutions and Newtonian fluids through two different model porous media having similar permeability: (a) a 3D random packed bed and (b) a microchannel with a periodically spaced pillars. The former provides much larger flow resistance at the same apparent shear rate compared to the latter. The flow profile in the 3D packed bed cannot be observed since it is a closed system. However, visualization of the flow profile in the microchannel shows strong spatial and temporal flow instabilities in VES fluids appear above a critical shear rate. The onset of such elastic instabilities correlates to the flow rate where increased flow resistance is observed. The elastic instabilities are attributed to the formation of transient shear induced structures. The experiments provide a detailed insight into the complex interplay between the pore scale geometry and rheology of VES in the creeping flow regim