Operating Dual-Completed Well to Increase Gas Recovery in Low Productivity Gas Reservoirs With Water Production Problems

Abstract

This paper presents a study into best design and operation of dual-completed wells with Downhole Water Sink (DWS) in low productivity gas reservoirs with water production problems. DWS is an alternative technology to Downhole Gas Water Separation (DGWS) by inclusion of a second (bottom) well completion isolated by a packer from the top completion.The bottom completion diverts water from the top completion so gas production is maximized and water-free.The study analyzed simulated performance of DWS wells for different values of well design parameters (the top and bottom completion lengths, and distance between the two completions), and operational parameter (the top/bottom completion rates, bottom hole flowing pressure at the lower completion, and the lead time when production comes only from the top completion-DWS start-up time). The simulations assumed strong aquifer support, and computed maximum gas recovery at the time when water loading occurs at the top completion.The study demonstrates that the presence of a separating packer between the two completions is critical for the unique hydraulics of DWS, i.e. isolation of two different bottom-hole flowing pressures. Also, the results show that the maximum advantage of DWS can be achieved when the top completion is short (penetrating top 20 -30 percent of the gas zone), bottom completion is long (penetrating the bottom part of the gas zone, or even the top of the aquifer), and the completions are as close as possible. Furthermore, water drainage should be postponed until water breakthrough occurs at the top completion. Then, water should be drained at maximum achievable rate to maximize gas production rate and delay water loading the top completion.

Water Production Problem in Gas Reservoirs: Concepts, Challenges, and Practical Solutions

“…Besides, it should not be postponed until the well is completely loaded with water. Moreover, six factors controlling DWS well performance were analyzed using a layer-cake type model to reach the best conditions by Armenta and Wojtanowicz [74].…”