Bayu-Undan Field: Appraisal and Development Planning
Authors: Reese Dave E. , Currie John C. , Chow Yit-Seng , Bhatia Mukul R. 
Published: December 2007

The Bayu-Undan Field - located offshore in the Timor Gap Zone of cooperation Area A (ZOCA) between Australia and Indonesia is a significant "world class" gas-condensate resource. A group led by Phillips Petroleum Company discovered the field in 1995 with the drilling of the Bayu #1. A group led by BHP Petroleum confirmed this discovery as a large accumulation with the drilling of the Undan #1. These two wells are 6 miles apart. This paper will present the results of the appraisal and conceptual development planning of the field to date.

Ten wells have been drilled into this normally pressured sandstone reservoir with consistent results as to the fluid composition and contacts. The reservoir contains a relatively lean gas-condensate whose tested condensate to gas ratio (CGR) is 60 bbls/MMscf. Laboratory testing indicates 2.4% liquid dropout. The gas-water contact (GWC) in all wells is located at 10197 ft subsea. Although large faults creating the possibility for several fault blocks are apparent in all of the seismic interpretations, the faults have not led to differing fluid compositions or contacts. The reservoir is comprised of a series of sandstone and shale intervals. In general, the upper part of the reservoir contains sands of lower net-to-gross and lower quality, while the lower part of the reservoir contains sands of higher quality with higher net-to-gross values. Core and drill stem testing has shown large variability in reservoir quality. Permeabilities from both core and drill stem tests range from less than 1 millidarcy to over 1 darcy.

Introduction

The Bayu-Undan Field was one of the most significant discoveries in 1995 in terms of total reserves of oil and gas. The field, located in the offshore Timor Gap Zone of cooperation Area A between Australia and Indonesia, is 280 miles northwest of Darwin, Australia (Fig. 1). The nearest landfall is approximately 130 miles north on Timor Island, Indonesia. The major part of the field lies in water depth between 230 to 300 feet. The field straddles two adjacent Production Sharing Contracts - ZOCA 91–12 operated by a group led by BHP Petroleum and designated Undan and ZOCA 91–13 operated by a group led by Phillips Petroleum Company and designated Bayu (Fig. 2).

The appraisal and development planning of the field is being carried out to commercialize the field at the earliest opportunity. The discovery well, Bayu #1, drilled by Phillips Petroleum Company intersected 575 feet of hydrocarbon column and the confirmation well, Undan #1, drilled by BHP Petroleum intersected 410 feet of hydrocarbon column. Both wells have the same GWC of 10197 feet subsea. To date, eight additional wells have been drilled, thus accomplishing a successful appraisal campaign. In the last twelve months, extensive subsurface and feasibility studies to finalize and optimize the development plan have been undertaken.

Geology

The Bayu-Undan Field is part of the greater Flamingo High within the northern Bonaparte Basin. The east-west trending Flamingo High is surrounded by north-northwest trending Flamingo and Sahul syncline and east-west trending Malita Graben, which may have been the source area for the Bayu-Undan hydrocarbons.

A thick sequence ranging in age from Triassic to Recent has been intersected in the area. The detailed regional geology has been documented by several authors. The description of the geology of the Bayu-Undan area is given in a paper by Brooks, et al.

The Bayu-Undan structure is a broad east-west trending horst with a number of culminations set up by internal faults (Fig. 2). The field covers an area approximately 18 miles in length and 9 miles in width. P. 401^