화학공학소재연구정보센터
Journal of Canadian Petroleum Technology, Vol.44, No.12, 49-54, 2005
Dual gas lift in wells with downhole water sink completions
Downhole Water Sink (DWS) technology controls water coning in dual-completed wells by concurrently producing water from the bottom completion below the oil-water contact, and oil from another completion at the top of the oil sand. It has been shown that DWS improves well productivity, increases oil recovery, and could produce oil-free water for direct injection or overboard dumping offshore. To date, DWS has been applied in natural now wells or wells where a downhole pump can be easily installed. However, in many areas, such as the Louisiana Gulf Coast and Venezuela where water coning is commonplace, the only production method is gas lift. This paper presents a feasibility study and a design method for dual gas lifting in DWS wells. The design employs a two-tier nodal analysis for several combinations Of two tubing strings - one for oil and a second one for water-installed in a production casing. First, nodal analysis is performed separately for the water and oil leas in order to define their operational range. Then, the two solutions are combined and coupled with the Inflow Performance Window (IPW) describing the operational domain (top inflow rate vs. bottom inflow rate) of the well. Using the new method, a simulation study was conducted using data from actual wells. The results indicate that the gas lift would limit the performance of DWS wells. Moreover, the design can be optimized for maximum production of oil with controlled water withdrawal from the bottom completion. Limitations such as maximum gas injection rate, or injection gas pressure, are discussed. Also, this paper presents an example of a theoretical performance of a DWS well with gas lift.