Enhancing Gas Flow – Dual Completion Wells
By perforating the casing both below and above the packer, as shown in figure 2-1, a lease operator can produce natural gas from two different zones simultaneously. Thus, a dual completion can double the intiial gas flow from a well. If, as often happens, the formation being drained by the tubing is depleted first, a serious problem arises. If the casing pressure substantially exceeds the tubing pressure, the tubing can collapse and gas flow to the tubing side of the wellhead tree will be restricted. If the casing side formation is first to depressure, an attractive opportunity may develop. A small hole, the size of a button, may be shot into the tubing string just above the packer. The flow of high pressure gas from the tubing into the annular space inside the casing, will act as lift gas. This lift gas will prevent the casing from loading up with liquids and thus surpress gas production. If this “button hole”, is made too large, a restrictive choke may be required on the casing’s gas production. This will probably negate the effect of the lift gas, as the restrictive choke will raise the pressure at the perforations above the packer in the same way as would liquid loading.
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