Abstract

Development of previously marginal fields in the Carnarvon sedimentary basin in Western Australia has been made possible by the use of monopod production platforms. The Bambra 3 project sought production platforms. The Bambra 3 project sought significant cost reduction through integration of the construction and drilling activities. During the project a method of fast installation of piles was developed and tested.

Introduction

Single column or monopod type production platforms are in widespread use. In size they vary from a conductor with wellhead in a swamp or lake to full size, multi-well production platforms servicing an entire field. The structures offer a number of advantages: in the single conductor case, economy; in the entire field case, provision of oil storage or resistance to damage by ice. In Western Australia they are utilized for economic reasons.

A number of offshore hydrocarbon discoveries have been made in Western Australia in the northern Carnarvon basin. It is the most prolific of the sedimentary basins in the state. Figure 1 shows the location; it is remote, the nearest major population center is Perth some 1200 km to the population center is Perth some 1200 km to the south.

To date six large gas fields and five commercial oilfields have been located. One of the larger gas fields and four of the oil fields have been developed and are being exploited.

Development of two of the smaller finds was delayed due to the high cost of conventional methods in these remote areas without resident development infrastructures. In both cases development was only made possible through the use of inexpensive, single column well platforms after previous attempts utilizing conventional structures had failed at the economic study stage.

The ability to take advantage of a drilling unit's availability for the installation work allowed a flexibility in programming the operations which lead to substantial savings. Simple structures were required which could be assembled without large shop or fabrication yard facilities and did not attract the high cost of marine transport from the south. Minimal structures with multi-function members (a beefed up well conductor acting as the main structural member), giving support and access to a number of surface wellheads provided the solution.

The Bambra project sought a further reduction in costs by integration of the drilling and installation phases of the development process and a reduction in risk, by allowing staged commitment, using a modular development approach.

BAMBRA FIELD

The Bambra hydrocarbon accumulation was discovered in 1982. The field is situated approximately 7 km north-west of Harriet oil field. The reservoir structure is a four way dip closed anticline. The reservoir formation is the Flag Sandstone section of the Barrow group. Reservoir characteristics are excellent with high permeabilities and strong water drive.

Bambra 1 encountered a gas/condensate zone. After reprocessing and remapping, Bambra 2 was drilled on a different high point of the same structure. Bambra 2 intersected an oil column under a gas cap. The well flowed oil and water during drill stem testing and was suspended as a sub-economic oil and gas discovery.

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