AN UNEXPECTED BENEFIT OF HORIZONTAL WELLS ON OFFSET VERTICAL WELL PRODUCTIVITY IN VERTICAL MISCIBLE FLOODS

Since 1989, Husky Oil has drilled 12 horizontal wells in six mature hy drocarbon vertical miscible flood pools. To date, these horizontal wel ls have been very successful in reducing gas coning and improving oil productivity((1)) as originally intended. Furthermore, actual field pe rformance indicates that, in some cases, horizontal wells have conside rably improved productivities of adjacent vertical wells. The drilling of a horizontal well in the Rainbow Keg River E Pool resulted in a 10 - 15% increase in oil production and a cessation in the rising gas-oi l ratio in the offset vertical wells. Such unexpected benefits are att ributed to improved drainage to the vertical wells induced by the dril ling of the horizontal well along with the healing and/or reduction of the gas cone at the vertical wellbores. These hypothesized causes for the unexpected benefits were qualitatively confirmed with a 3-D numer ical simulation model. It is concluded that drilling of horizontal wel ls can improve the productivities of offset vertical wells. The fear o f drawing gas over to a horizontal well that is drilled close to gas c oning vertical well(s) may be unfounded under most situations. After d rilling a horizontal well into a target area, the lateral section can be extended to cover areas near offset vertical well(s) to improve dra inage and reduce some of the gas coning tendencies around the offset v ertical wellbore(s).