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ABSTRACT

The Phillips Petroleum South Timbalier South Addition 260 #1 well, Teak prospect, tested a subsalt closure covering parts of three offshore blocks. The structure was formed by the truncation of southeast dipping strata on the north and west by salt welds. These welds, which juxtapose strata of different ages and geometries, are collapsed salt feeder systems that were the conduits for emplacement of the salt sheet overlying the Teak prospect.

The well encountered eight hydrocarbon shows over 5000’ of subsalt section in predominantly thin-bedded turbidite sandstones interpreted as overbank-levee and splay deposits. Pay intervals are confined to a zone directly below the salt and deeper in the section below an unconformity surface. Salt welds proved to be sealing surfaces, but other parameters also influenced the vertical distribution of hydrocarbons. The hydrocarbons directly below the salt are trapped within a tectonically disturbed zone where reservoirs probably have limited lateral continuity due to faulting and sediment disruption caused by movement of the overlying salt. The deeper unconformity is interpreted as an older salt weld below the present-day salt sheet because of missing stratigraphic section and the presence of a condensed section above it.

A tectonic model for the area indicates three phases of salt movement. The first phase was a near-vertical emplacement of areally-restricted, wedge-shaped salt massifs related to large counter-regional faulting which occurred during the late Miocene. This was followed by rapid deflation of the massifs and large sediment accommodation during the early Pliocene which emplaced the salt over Teak, forming the bounding weld surfaces. Finally, a period of thin-skinned extension during the late Pleistocene remobilized the salt sheets into secondary piercements, forming sub-horizontal welds extending away from the present Teak salt sheet.

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