Unlocking The Potential: A North Sea Heavy Oil Success Story
- Jonathan James Wylde (Clariant Oil Services) | Gareth D.M. Williams (Clariant Oil Services) | Richard Cousins (BP Exploration and Operating Company Ltd)
- Document ID
- Society of Petroleum Engineers
- SPE International Thermal Operations and Heavy Oil Symposium, 1-3 November, Calgary, Alberta, Canada
- Publication Date
- Document Type
- Conference Paper
- 2005. SPE/PS-CIM/CHOA International Thermal Operations and Heavy Oil Symposium
- 4.3 Flow Assurance, 5.1.1 Exploration, Development, Structural Geology, 4.1.4 Gas Processing, 6.6 Sustainability/Social Responsibility, 5.6.4 Drillstem/Well Testing, 4.3.1 Hydrates, 6.5.2 Water use, produced water discharge and disposal, 1.11 Drilling Fluids and Materials, 1.6.9 Coring, Fishing, 4.5 Offshore Facilities and Subsea Systems, 5.6.8 Well Performance Monitoring, Inflow Performance, 4.9 Facilities Operations, 4.3.3 Aspaltenes, 1.6 Drilling Operations, 5.1.2 Faults and Fracture Characterisation, 5.2.1 Phase Behavior and PVT Measurements, 5.5 Reservoir Simulation, 4.2 Pipelines, Flowlines and Risers, 6.1.5 Human Resources, Competence and Training, 4.1.5 Processing Equipment, 5.2 Reservoir Fluid Dynamics, 4.1.2 Separation and Treating, 4.2.3 Materials and Corrosion, 4.3.4 Scale
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This paper gives details concerning one of the newest producing fields in the North Sea, West of Shetland development. Examples of the pre-start up design and implementation challenges are dwelt on, as well as the philosophy taken when commissioning the plant and chemical injection facilities. The majority of the paper focuses on the first 6 months of production history and the way in which the management of production techniques was performed and in particular how actual operations differed to the planned and designed specifications.
With production of a 20° API crude, significant operational challenges have been encountered with initial start up being a staged and controlled process. Details are given to the suite of production chemicals required to give complete flow assurance as well as to maintain plant integrity. The onset of water production brings with it a whole suite of different challenges with by far the most difficult being demulsification and this has been given particular attention.
CLAIR FIELD BACKGROUND
The Clair Field is located 75 km (40 miles) west of the Shetland Islands and is currently produced from a single fixed platform in 140 m of water (Figure 1). The field produces both oil (exported down a dedicated pipeline to Sullom Voe Terminal (SVT), Shetland) and gas (ties into the existing West of Shetland Pipeline, to SVT) with a GOR of 550 scf/bbl. The Clair reservoir extends over an area some 40 km by 20 km in complex Devonian and Carboniferous units covering 5 licence blocks (206/7a; 206/12; 206/8; 206/13a and 206/9). Current estimates of the likely oil are in excess of 4 billion barrels STOIIP, making Clair the largest undeveloped hydrocarbon accumulation in the UK Continental Shelf and a key component of future UK production strategy.
The Clair Field was originally discovered in 1977 but a poor understanding of the reservoir properties (significant faulting and fracturing) combined with a competitive exploration and appraisal programme through the 1980s by the original four licence groups prevented a commercial development. In the early 1990s acquisition of 3D seismic data over the whole field occurred, and two wells were drilled in 1991 and 1992. Although they demonstrated commercial flow rates, the wells were not produced for long enough to give confidence in long term reservoir performance. In 1996, an extended performance test was conducted on well 206/8-10z in the core area. Flowing at an average rate of 10 MDB for 23 days, with a peak of 18.5 MBD, the well performance changed the perception of the Clair reservoir by demonstrating sustainable crude oil delivery.
The extent of the Clair field demands that it be produced as a phased development. The first phase builds on the successful 1996 well test and targets development of the Core, Graben and Horst areas (Figures 1 and 2). The reservoir is divided into nine fault-bounded segments having a common free water level and maximum oil column of 600 m. A gas cap is present in the structurally elevated ridge segments. The reservoir depth is 1,850 m TVDss and the initial reservoir pressure was 192 Barg with a temperature of 66.1°C. Work is continuing to define this first development and has already begun with Clair Phase 2. The challenge for Clair is in understanding the issues of reservoir deliverability, well productivity and managing the cost base whilst adhering to the aspirations for a sustainable development. Clair will be the third West of Shetland development after Foinaven and Schiehallion.
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