This paper describes the field application of a novel wireline conveyed cased-hole formation dynamics tester designed to drill a hole in casing, measure formation pressure and permeability, identify and retrieve downhole fluid samples and seal the hole with a bi-directional plug. Until recently the only way of obtaining such information in cased hole was either by performing aDST or using a modified open-hole tester (needing explosives and squeeze cementing). The Sembakung field, N.E. Kalimantan was discovered in 1975 and has produced over 37 MMBO. The main producing interval is the Upper Middle Miocene Tabul formation. Over 35 separate sands have been identified in this highly stratified reservoir and producing wells have multiple commingled zones. The reservoir and crude quality is good (f=15–30%, K=200–2000 mD, 37 API, low-sulphur low-wax). Equatorial Energy acquired an 80% stake in the TAC in 1998 and commenced an aggressive program of infill drilling, as well as acquired a 3-D seismic surveyin 2001. 3D seismic uncovered the presence of a significant southward structural extension with additional exploration potential. It also revealed the existence of new untapped reservoirs and structural compartmentalization within the field. Declining pressures and signs of inter-well communication indicated the urgency of field pressure maintenance. Drillstem testing was not feasible as a large number of potential zones needed to be tested. This novel tool proved useful in managing the challenge. The tool was run successfully in 7 wells where it drilled and tested 71 holes in casing and recovered fluid samples. Formation pressures were measured, permeabilities estimated and fluids identified using downhole pump out with optical spectroscopy. The performance conclusively demonstrated the applicability and cost-effectiveness of this novel technique in revival of this oilfield. Sembakung Field The Sembakung field is located in N. E. Kalimantan state of Indonesia and lies in the oil and gas bearing Tarakan basin of onshore North-East Borneo. The location map is shown in Figure 1. Stratigraphically, the Tarakan basin consists of a prograding deltaic sequence from upper Miocene through Pliocenetime. Figure 2 shows the typical stratigraphy of the Tarakan basin. Fields in the basin produce from stacked deltaic sands of Miocene and Pliocene age instructurally controlled traps. Ref. 1 gives a good account of the tectonic history and hydrocarbon geology of the Tarakan basin. The Sembakung feature is a northwest to southeast oriented anticline with abroad northern end and a steeper western flank. The west and east sides of the anticline are bounded by high angle thrust faults forming a reverse flower structure (Ref. 2). Figure 3 is a northwest to southeast seismic cross-section across the Sembakung field, which clearly brings out these features. The main productive interval in the field is the Upper Middle Miocene Tabul formation consisting of thinly interbedded sands and shales. The field is shallow, with the sands occurring over the interval –1600 to –3500 ft subsea. About 35 different sand groups have been identified varying in thickness from a few feet up to 30 feet. A majority of the production comes from the 24 AB to 28sand interval. Figure 4 is a structure map of zone 24 CD, which is one of the main producing sands. The field has been producing since 1977 with a maximum initial production of11,700 BOPD and cumulative production of over 37 MMBO. The field had since then been left on natural decline with a low production rate. Equatorial Energy acquired the field in 1998, carried out a 3-D seismic survey and redeveloped it with closer infill drilling. A significant southward structural extension was found and previously untapped reservoirs identified. Current oil production from the field stands in excess of 7000 BOPD.

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