Abstract

BP's Harding Development employs a totally innovative concept for North Sea oil production. A large permanently installed jack-up platform, incorporating production, drilling and living quarters facilities, is positioned on top of a concrete gravity storage base tank which holds Harding's acidic heavy crude before export, via a submerged turret loading buoy, to shuttle tankers. The use of horizontal drilling techniques in the early 1990's coupled with adoption of the above concept transformed a very marginal prospect into a viable development which currently has one of the lowest development costs per barrel in the North Sea.

The paper describes how the viability of the development has been achieved using an entirely new approach to project management by BP with a small integrated management team. The relationships created with design contractors, suppliers and fabricators are shown to represent the embodiment of the principles of the CRINE initiative and have secured for all parties benefits which can be used as benchmarks for future projects in a low oil price environment. Contractual arrangements are discussed and a new approach to Operations and Maintenance support contractors is highlighted.

The concept has potential for reducing abandonment costs due to the relative ease of decommissioning and removal.

Introduction

The Harding Field, originally known as the Forth Field, is a Eocene accumulation located some 320 km north east of Aberdeen in block 9/23b of the northern North Sea. The field, which was discovered in 1988, comprises four reservoirs containing a heavy, naphthenic crude (18 – 28 API, TAN Number 2.8) with a low gas/oil ratio (240– 310 scf/bbl). The two largest reservoirs, Central and South, are being developed as part of the current project programme. The combined recoverable reserves amount to some 185 mmbbls.

Following the initial discovery, a drilling programme was established and in parallel, a series of conceptual studies undertaken to identify viable development options for the Field. Based on the technologies available at the time, the indications from these studies were that an economical case could not easily be made for the field's development. A single, jacket-supported production facility drilling vertical wells over the Central reservoir with subsea tie-backs from the South reservoir appeared to be the only technically feasible concept.

The successful application of horizontal drilling techniques in the early 1990's provided the trigger for a further round of concept reviews. A conventional single production and drilling platform located between the two reservoirs and accessing them via horizontal wells was deemed to be achievable but costs were still providing a barrier to a viable project. In the context of a falling oil price, a highly innovative scheme was required that would drive the development costs per barrel down to a level that was substantially lower than that which had been achieved at the turn of the decade. Eventually, the use of a large purpose-built permanently installed self-elevating jack-up platform was assessed and seen as a preferred solution to overcome the economic hurdles and meet the challenge of a development cost target of less than $4/barrel in a world of $14 oil.

The characteristics of Harding's crude are such that it cannot be blended at peak design production rates of 63,000 bbls/day into the adjacent Forties Pipeline System. A totally submerged concrete gravity base tank (GBT) was identified as suitable storage for the crude until such time as it could be uplifted via shuttle tanker for transportation to refineries capable of handling its special characteristics. The GBT performs two roles in that it provides storage capacity for 580,000 barrels of stabilised crude prior to tanker shipment and acts as the foundation structure for the jack-up. The last major link in the development scheme is the 24" diameter export line, terminating in a Submerged Turret Loading (STL) system.

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