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Through-Casing Formation Tester Provides Answers for Rejuvenation of a Mature Oilfield
Until recently the only way to obtain formation pressures and samples in a cased hole was either by performing a DST (with attendant risks and emissions) or by perforating and testing the formation using a modified open-hole tester (needing explosives and squeeze cementing). This paper describes the field application of a wireline conveyed cased-hole formation dynamics tester that is designed to drill a hole in casing, measure formation pressure and permeability and retrieve samples. The formation fluids can be identified in real-time using downhole optical spectroscopy and a pumpout module. If required, the hole can then be sealed with a plug rated to 10,000 psi (bi-directional).
The Sembakung Field, located in N.E. Kalimantan, has produced over 37 MMBO since its discovery by ARCO in 1975. The Upper Middle Miocene Tabul formation is the main producing interval. This highly stratified reservoir consists of over 35 separate sands and producing wells usually have multiple commingled zones. The quality of both reservoir and crude oil is good (porosity 15-30 %, permeability 200 mD to Darcies, sweet crude of 37° API gravity).
Equatorial Energy acquired a majority share in the Technical Assistance Contract Block in 1998, acquired a 3D seismic survey and commenced a comprehensive re-development program. The 3D seismic revealed the presence of a southward structural extension with significant exploration potential.
Redevelopment revealed the existence of new reservoirs and compartmentalization within the field. Since a large number of potential zones had to be tested, drillstem testing was not feasible. The Cased Hole Formation Dynamics Tester (CHDT®) proved useful for this task. The tool was run successfully in 3 wells where it drilled 19 holes (12 left unplugged on operator's request) and recovered 2 fluid samples. Formation pressures were accurately measured and permeabilities estimated. Formation fluids were identified downhole in real-time using optical spectroscopy. The CHDT proved efficient and cost-effective in redevelopment of this oilfield.
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