EVALUATION OF POLYMER INJECTION, NEAR-WELLBORE, AND IN-DEPTH GEL TREATMENTS IN A STRATIFIED POROUS MEDIUM

摘要

In this work, water–oil displacement in a stratified oil reservoir was studied, using field-scale numerical simulations, and the effect of polymer injection, near-wellbore and in-depth gel treatments on oil recovery enhancement were evaluated. Water channeling, i.e., the main governing phenomenon in the studied cases, was highly affected by the permeability ratio between the layers and water/oil mobility ratio; and to some extent by other parameters including crossflow between the layers, reservoir dip, vertical permeability, the relative position of the layers, and the injection flow rate. As the permeability ratio between the layers increased from 5 to 1000, or by increasing oil–water viscosity ratio from 1 to 20, the water breakthrough time was almost 10 times shorter and the oil recovery factor was approximately halved, after 3 pore volume water injection. Relative position of the high and the low-permeability layers influenced oil recovery, due to the gravity drainage effect. This effect was pronounced at lower injection flow rates. Increasing the dip angle in the up-dip reservoir resulted in higher oil recovery and sharper displacement. Injection of a polymer slug resulted in a short-term water cut reduction and a jump in oil recovery (up to 20%); however, as polymer slug was diluted and displaced by the subsequently injected water, mostly through the high-permeability layer, the long-term recovery factor approached that of the waterflooding, especially in the cases with lower oil–water viscosity ratios. Enlarging the slug size of polymer was more effective than injecting more viscous polymer. Increasing the polymer viscosity up to 50%, did not improve oil recovery factor. In the reservoir with communicating layers, in-depth gel treatment resulted in almost 5% incremental oil recovery after 5 pore volume water injection; while less than 2% recovery improvement resulted by near-wellbore treatment. It was demonstrated that increasing gel-treated length and strength are more effective than the depth of treatment, especially in the long term.