4.7. Mechanism of EOR with membrane technology
Enhanced oil recovery with osmotic pressure from fractured
reservoir includes three key steps. The first step is to determine
the salinity of formation water in the matrix. The second is to form
a semi-permeable membrane on the surface of fractured reservoir
by injecting fluid containing membrane-forming materials. And
the third is to inject a fluid with a low solute concentration
(compared to the formation water in the matrix) to displace the
water in the natural fracture and leave the membrane in place. In
such case a chemical potential or solute concentration gradient
was established across the membrane. Under this condition the
osmotic phenomena will spontaneously occur. The osmotic pressure causes parts of the low-solute fluid in the natural fractures to
move across the semi-permeable membrane into the matrix, and
displace the oil in the pore into the natural fractures until the
chemical potential gradient and the hydrostatic pressure reaches
equilibrium