Foam assisted lift (FAL) is one of the common deliquification techniques that is applied in different forms. However, achieving sustainable improved performance in practice from case to case is yet a challenge. This paper shares the journey that PDO has gone through so far in assessing and applying foam assisted lift technology, and the strategy that is emerging from this journey. The paper sheds light on challenges and lessons learned by sharing both successful as well as unsuccessful cases to provide a comprehensive picture. Proper candidate selection as well as selecting different implementation methods for different cases are the key learnings and yet challenges in practice that this paper elaborates on.
The installation of a smaller size tubing or velocity string inside an existing tubing completion is a well-known deliquification technique. The velocity string comes in various designs providing different functionalities for deliquification. Typically, velocity strings are installed to the top of the producing reservoir interval. In case multiple reservoirs produce across significant liner length (the liner here is the length/area between the two reservoirs), this "shallow" velocity string does not provide deliquification across the reservoir liner section. Depending on the size and length of the reservoir liner and the inflow performance of the producing reservoirs, the liquid loading across the liner can have significant adverse impact on production in which case deliquification by means of a "deep" velocity string installed across the reservoir liner becomes essential. This paper shares different designs, a modeling methodology and real-life assessment cases of such deep-set velocity strings, to achieve deliquification across the tubing completion above the reservoir and the liner completion straddling the reservoir. The proposed designs provide different flow options by changing the setting of sliding side doors (SSD's) embedded in the design or isolating the two zones by packers. The proposed modeling methodology helps to compare the performance of different flow options for shallow and deep velocity string designs. This paper continues by sharing three field cases of deep-set VS for the assessment of its real-life application.
Following the reduction of system pressure through depletion compression more than 150 deep gas wells started struggling from halite deposition. Halite deposition in the completion restricted or blocked the production from the lower reservoir in these wells and reduced the total gas production of the field by about 40%. Meanwhile, many of the wells with halite deposition issue were also suffering from liquid loading and velocity strings were isntalled in them as the primary means of gas well deliquification. Many of these wells with velocity string showed no further halite deposition due to increase of the bottom hole pressure and reduction of the draw-down. Consequently, frequent freshwater bull heading or clean out with coiled tubing were no longer needed. This observation triggered the idea to create synergy between gas well deliquification and halite management through installation of velocty string. This synergy does not exist in every case, and this paper elaborates on identifying where it exists.
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