Fluid flow at the edge of SAGD chamber where most of bitumen drainage occurs is of great importance. In this region, water condensate co-flows with the falling bitumen towards the production well. Since the bitumen viscosity varies at different locations due to temperature gradient across the edge of steam chamber, new correlations are required to consider the influence of fluid viscosity on the relative permeability curves. In this study, the objective is to remedy this deficiency by developing a new set of correlations for relative permeability estimation addressing in particular such effect at SAGD steam chamber edge.
Various datasets from literature were obtained at different temperatures and oil viscosities. The data were used to develop new correlations which are a modification of the well-known Corey's equations for relative permeability estimation. Two mathematical approaches were applied and evaluated to achieve the best correlations: (1) at each temperature, herein substituted by viscosity ratio, relative permeabilities are functions of saturation, and (2) relative permeability is a function of viscosity ratio at a fixed saturation. Furthermore, different mathematical equations were used in the regression procedure in order to optimize the objective function and achieve the most reliable correlations.
Results indicated a combined power and quadratic functionality of relative permeability to the phases’ viscosity. The viscosity ratio was used in the new correlations as a dimensionless parameter which represents fluids’ viscosities at different temperatures. The new correlations were compared against the original Corey's equations for various experimental datasets. Various statistical error formulation were employed: average relative error, average absolute relative error, root mean squared, correlation coefficient, and standard deviation. The accuracy of the new correlations was also graphically compared with Corey's model using cross-plot illustrations. Comparative evaluation of these correlation error analyses revealed that relative permeability estimations have been significantly improved when new correlations were employed which incorporate different temperature profiles and accordingly the viscosity variations. The application of the new correlation could improve the flow prediction in thermal simulators.
In this study, gas-oil gravity drainage process and steam-gas assisted gravity drainage processes for heavy oil recovery from fractured models were investigated experimentally. For each test, six oil- wet saturated outcrop cores, 8.7 cm in diameter and 15 cm length, were stacked in a long core holder. In the first step, gas injection was started into the model at reservoir condition that results in oil production under gas-oil gravity drainage mechanism. In the second round of tests when no more oil was produced by gas injection, the tests were continued using steam-gas assisted gravity drainage process. In this stage, gas was injected together with specific steam/gas ratio at saturated temperature condition. In the course of experiments, oil and water productions, pressure and temperatures of system were monitored carefully. The experiments were performed using three different combination of gases consist of pure CO2, pure N2 and mixture of 15 % CO2 and 85% N2 as synthetic flue gas. The results showed that after gas breakthrough and fracture depletion, the ultimate oil recovery for CO2 injection was 58.4 % (14.8% for gas injection and 43.6 % for steam-gas co-injection), in the case of flue gas injection, it was 73.8 % (9.8 % for gas injection and 64% for steam-gas co-injection) and for N2 injection was 47% (13.5 % for gas injection and 33.5% for steam-gas co-injection). The results indicate the high performance of flue gas injection for heavy oil recovery from fractured reservoirs during gas-oil gravity drainage and steam-gas assisted gravity drainage processes.