Discussion on the development technology policy of gas cap and bottom water reservoirs with interlayer

Reservoirs with gas cap and bottom water are exposed to the risk of the situation that the oil and gas are mutually turbulent in the development process. The development of the interlayer can prolong the gas-free and water-free oil recovery period in a single well, control the bottom water coning speed and improve the oil recovery. Therefore, the key to efficiently explore such reservoirs is to seek the interlayer and avoid the turbulence. The Z reservoir is a typical reservoir with gas cap and strong bottom water containing a uniform oil-gas interface and oil-water interface. Interlayers with certain permeability are continuously distributed in the middle part of the reservoir, and it is quite different between the reservoir above the interlayer and below the interlayer in terms of properties. The development technology policy of such reservoirs was established by means of reservoir numerical simulation. The influence of the interlayer on the development index and the development technology strategy of the Z reservoir were studied. According to the research, it is believed that the development of such reservoirs should adopt the method of “drawing the layer system and making regional separation”. According to the reservoir feature, the reservoir is separated to two development systems and three zones by interlayer. The zone I of reservoir above the interlayer is developed according to the reservoir with gas cap and bottom water, and try to avoid the way of oil and gas producing together. The zone II of reservoir below the interlayer is developed according to the reservoir with bottom water. The wells are mostly located closed to the interlayer. The research results show that when the well is drilled under the interlayer, it can slow the gas coning speed and control the gas production rate. But when the well is drilled at the top gas zone, it cannot stop the oil from going back to the top gas zone. Reservoir above the interlayer was developed according to the reservoir with gas cap and bottom water, and reservoir below the interlayer was developed according to the reservoir with bottom water. In addition, it had better development effect on firstly develop of the bottom layer considering the maximum oil recovery factor and high initial oil rate. The optimum number of wells in bottom reservoir is four, and the optimal production allocation is 1500 m³/d. The optimum number of wells in edge reservoir is two, and the optimal production allocation is 100 m³/d.