M. Robin (Inst. Francais du Petrole)
During steam injection operations, the sweep efficiency is detrimentally affected by gravity effects or reservoir heterogeneities. In order to increase the sweep efficiency, research is being done on combined steam and surfactant flooding, causing the generation of foam; this would plug off the preferential flow paths, reduce the gas mobility, and enable the steam to invade a larger portion of the reservoir.
A laboratory study was carried out to determine and follow the evolution of foamability from ambient conditions up to about 300 degrees C and 10 MPa (572 degrees F and 1450 psi), corresponding to high pressure steam injection. Foam efficiency was evaluated by displacement tests in porous media.
For most of the currently used surfactants, foam stability is dramatically affected by the presence of a residual oil phase. Moreover, the efficiency of foams decreases considerably when temperature increases.
Testing various surfactants in the presence of oil enabled us to screen some chemicals that form foams whose stability is not affected by the contact with a hydrocarbon phase. The pressure drop during foam injection is studied versus temperature and foam quality, in a homogeneous porous medium.
Blocking properties of foams generated by different surfactants are compared under various conditions.
Work has been done under laboratory conditions to visualize the mechanisms of foam action for increasing oil recovery, in cores which are either homogeneous or constist in two layers with different permeabilities. A considerable difference is noticed between the usual surfactants and certain chemicals which are not affected by the presence of oil.
It can be observed that foam stability decreases severely with rising temperature. This effect can be reduced by adding some appropriate compounds to the surfactant solution, prior to injection.
Results of displacement tests performed in cores with crude oils, under steamflood conditions, show a significant increase in recovery due to foam efficiency. These experiments were mainly conducted under isothermal conditions.