Using the enabling technology of a solid expandable liner system allowed Edison–Milan to cost effectively convert a producing well in Italy to a gas storage monitoring well. The solid expandable liner allowed for the execution of two objectives in a one step operation; sealing off old production perforations and placing a mechanical barrier over a reactive shale formation in the openhole section immediately below the shoe of the previous casing string. The larger post expanded diameter of the combination openhole / cased-hole expandable liner also facilitated the eventual installation of larger diameter gravel pack (GP) screens.
This well required the isolation of old perforations in the toe of the casing as well as a need to cover an "active shale" section in the open hole. While the perforations could have been isolated by squeezing with cement and drilling out, the active shale would still cause a major problem when pumping the gravel pack. Being active means that when pumping fluids in the well, the shale could collapse or swell in on the completion equipment, causing installation problems.
Mitigating the old perforations and then fighting the active shale formations would cause non-productive time (NPT) and could have a large impact to the cost of the well. Additionally, the use of smaller gravel pack screens could impact the economic viability of the well.
The combination openhole / cased-hole solid expandable liner was run in order to isolate the perforations and blank off the active shale section in the open hole. The next hole section was drilled and a GP system was installed. The top of the GP packer was set above the solid expandable liner. The GP assembly and screen were run through the expandable liner into the target zone in the open hole.
The screen sizing is critical on gas storage, as the larger the screen the greater the production/injection rates that can be achieved. If a select screen has a base pipe that is too small, high erosion can occur across the screen wrap/weave, causing catastrophic results including total sand control failure. The solid expandable liner allowed a 4 in. diameter screen to be utilized rather than a 3-1/2 in. diameter screen.