Being able to capitalize on advantageous mechanical isolation technologies has been the catalyst for some operators to utilize existing wellbores to optimize field recoveries from different reservoirs. An innovative application that installed over 1,400 ft of solid expandable tubulars enabled Marathon Oil Gabon Limited (MOGL) to simultaneously isolate a sour zone produced through casing perforations and segregate a previously repaired multi-stage cementing collar in their Tchatamba South B2 sidetrack (TCTS B2st) well in Gabon. The solid expandable cased-hole liner allowed MOGL to develop a lower zone and continue producing from the existing well.

This value-added approach was even more economically prudent because MOGL used a hydraulic workover unit (HWO) in this well intervention as an alternative to a conventional rig. The increasing cost and unavailability of drilling and workover rigs, mainly offshore, have become contributing obstacles for well intervention and well repairs in mature fields. In this case solid expandable tubulars mitigated production problems and extended the life of the well with lowered costs and increased reliability. This paper describes the safe and successful installation of a solid expandable tubular system that isolated six individual sets of perforations into four intervals. This system also reinforced the integrity of a previously repaired, multi-stage cementing collar, accomplishing both objectives with a minimum reduction to the existing inside diameter (ID) of the wellbore. The paper also details how this enabling technology allowed MOGL to perforate and produce a deeper zone thus optimizing reserve recovery in a mature field.

Field Conditions and Relational Wells

The Tchatamba Field, located in 162 ft of water offshore Gabon, consists of two stand-alone platforms, the Tchatamba West and the Tchatamba South, and a mobile off shore production unit called the Tchatamba Marin (Figure 1). A total of nine wells on artificial lift via electric submersible pumps (ESP) produce from three reservoirs-Madiela, Cap Lopez, and Azile. Wells in the Tchatamba field are pumped without an ESP packer or a surface-controlled subsurface safety valve (SCSSV) once reservoir pressures deplete to the point they are incapable of flow to surface. This simplifies ESP installation and production operations. Operational limitations dictated the recompletion of the Tchatamba South 2ST (TCTS 2ST) well. The recompletion operation called for isolating the shallow, sour Azile reservoir and perforating two previously undeveloped zones of the Madiela to optimize field production and increase overall recovery.

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