The coning problem for vertical wells and the ridging problem for horizontal wells are very difficult to solve by normal methods in the process of producing oil from the reservoir with bottom water drive. For heavy oil reservoirs, this difficult problem becomes more complicated for the non-Newtonian properties. An innovative completion method with downhole water sink was presented by dual-completed in oil and water columns with a packer separating the two completions for vertical wells and dual-horizontal wells that the upper well produce the fluid over the oil water contact (OWC) and down well the lower well produce the water below the OWC. The unique technique may restrain the formation of the water coning and ridging by adjusting production rates upper and lower OWC and enlarges the oil draining area, which in turn improve the oil recovery.
In order to evaluate quantatively the production performances by using the new method, numerical simulation technique was employed to find out optimal perforation segment and fittest production rates from the formation of the upper and lower OWC.
Water coning has been regarded as the biggest problem during the oil production from a reservoir with bottom water. The phenomenon has been known for at least 100 years. The theory of water coning has been discussed by Smith, C.L.1 62 years ago and some other previous researchers before him. Resumptively, the occurrence of water coning is due to pressure gradients resulting from well production from the pay zone. The pressure gradients result in a water cone to rise toward the bottom of the producing interval. The tendency of the water to cone is offset or partially offset by gravity forces since the water has a higher specific gravity than the oil. A dynamic balance exists between the gravitational forces and the pressure gradients caused by well production. If the pressure gradient exceeds the gravitational force, water coning to the wellbore will occurs.