Abstract

In the last three years, two significant commercial hydrocarbon accumulations in Indonesia deep waters of the Makassar Strait were discovered. These fields are located approximately 16 miles northeast of the giant Attaka Field in 1400 ft to 3400 ft of water.

To date more than 40 exploration and appraisal wells have been drilled in both fields and extensive pressure data has been collected by formation tester tool and drillstem testing tool. The pressure data, used with other data suchas seismic and well logs, has enabled Unocal Indonesia to characterize deepwater turbidite sand reservoirs.

In this deepwater environment, DST is used selectively and only with strong justification due to its prohibitive cost. Instead, the use of the pressure testing tool is pushed to its limit in order to gain extensive pressure, rockand fluid properties data, conventionally obtained by DST.

This paper will show the experience of Unocal Indonesia to characterize deepwater reservoirs by means of pressure data from the formation tester tool and DST's to complement geological and seismic data interpretations. Reservoir characteristics such as fluid type, fluid contacts, reservoir connectivity and sand geometry can be inferred from the pressure gradients and pressure transients. These data are used in constructing reservoir fluid flow models for field development plan.

Introduction

Since early 1990's Unocal Indonesia Company has been employing acost-effective philosophy in exploring and developing fields in the continental shelf of the Mahakam Delta, offshore East Kalimantan, Indonesia. Through the drill bits, their operations are specially designed to sufficiently capture reservoir data in a cost-effective way by carefully selecting between "wants" and "needs" while gathering data. Experience gained over the years from drilling to formation evaluation has resulted in the continuing refinement of the tools and techniques involved to implement these programs. As the company pushes their exploration beyond the shelf into the deepwater in this known hydrocarbon province, this cost-effective practice again provides the backbone for exploration in this new frontier1.

This paper presents a case study that demonstrates the integration of dataderived from different sources to characterize complex hydrocarbon-bearing reservoirs recently discovered in the deepwater of the Makassar Strait, Indonesia. The key to understanding these reservoirs that lead to their approved development plan stems from a cost-effective data acquisition programwith focus on extensive collection of reservoir data from formation tests. The paper describes how this abundant, less-expensive source of data is used together with data from other sources; such as cores, seismic, logs, and drill-stem testing, to characterize complex turbidite sandstone reservoirs. On the basis of this data, reservoir simulation models are constructed to forecast potential oil and gas recoveries and to drive the field development plan. The methodology employed in constructing these models and key reservoir parameters that influence the decision to select a specific plan of development are alsodiscussed.

Deepwater Geology in the Makassar Strait

In 1996, Unocal Indonesia began its exploration program in Indonesia deepwater in the Makassar Strait, offshore East Kalimantan. Since then, two significant oil and gas accumulations among others have been discovered lyingin the deepwater of this known hydrocarbon province. Located approximately 16 miles ENE of the giant Attaka Field, these new fields are in water depths ranging between 1400 to 3400 (Figure 1).

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