Study on optimal vertical position of horizontal well in gas-cap reservoir

The horizontal well is an effective way to avoid early gas breakthrough of gas cap reservoir and the identification of its optimal vertical location is the key to obtain the best development result.Through analyzing the effect of the vertical locations of horizontal wells on the critical output and gas breakthrough time of the gas cap reservoir,the curve showing the relationship between the vertical locations of horizontal wells and the critical output as well as the gas breakthrough time is obtained in this paper.After taking both critical output and gas breakthrough time into consideration,the obtains the curve showing the relationship between the vertical locations of horizontal wells and the arithmetic product of critical output and gas breakthrough time.According to the curve tendency,the range of the optimal vertical locations of horizontal wells in gas cap reservoirs is obtained as well.The research shows that the critical output will increase and the gas breakthrough time will become shorter if the horizontal well gets closer to the gas cap.The best development effect will be achieved if the distance between the horizontal well and the oil-gas interface accounts for 80% to 90% of the oil bearing thickness.This can supply basis for reservoir engineering design of the horizontal wells in gas cap reservoir.