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Abstract

In August 1998 Unocal Indonesia drilled the discovery well for the West Seno Field located in the Kutei Basin offshore East Kalimantan, Indonesia. Following an accelerated delineation program, a Plan of Development was submitted and approved in September, 1999, which served to commercialize the Makassar Straits Production Sharing Contract (PSC) area.

In the West Seno area, hydrocarbon accumulations occur where upper and middle Miocene sandstones are fault and stratigraphically trapped in an updip position. The lateral continuity of seismic reflectors, biostratigraphic analysis, and well log data in the West Seno area suggest the sand-prone intervals display significant lateral distribution. These sandstones are interpreted to be amalgamated, turbidite channel sands associated with interbedded, levee-overbank sand/shale sequences deposited in a mid-slope position. Porosity in the reservoir sandstones ranges from 22 to 32 % and permeability ranges from 150 to 1500 mD. Productive sandstones are characterized by resistivity readings ranging from 4 to 20 ohms. Core data show that low-resistive pay intervals, with 4 to 5 ohms resistivity, are characterized by reservoir bed thickness ranging from millimeter to centimeter scale, interbedded with shale and carbonaceous laminae of similar bed thickness.

Geochemical analyses of the Miocene oils and gases demonstrate they are most likely derived from predominantly terrestrial plant organic material. The hydrocarbons found in West Seno are interpreted to have migrated vertically along faults from the source area to the upper Miocene reservoirs. The oils are all good quality crude having an API gravity range between 35 to 46 degrees.

Data gained from conventional cores, special petro-physical logging tools, and drill stem tests were used to construct a petrophysical model to calculate reservoir properties used in the quantification of the West Seno Field reserves.

The West Seno Field is a “fast tracked” project; only 14 months from time of first discovery through to Plan of Development approval. This will be the first deepwater development for Indonesia and for Unocal; expected first production will commence in 2002.

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