BP has been developing an integrated and systematic approach for the early assessment of deepwater geohazards to support planning and design of several major gas field development in the West Nile Delta (WND). The approach has involved the assembly of a team of experienced geoscientists from the disciplines of geology, geophysics, geomorphology and geotechnics. The paper will demonstrate the value of early engagement of multidisciplinary team approach for the evaluation of 3D exploration-quality seismic data in frontier deepwater areas where the issue of geohazards could be a potential major constraint to the siting of tophole locations and facilities. Early screening of the geohazard challenges to development can be used to guide the appropriate level of investment, resources and data acquisition programme to support subsequent stages of the project.

Early acquisition and calibration of field-wide autonomous underwater vehicle (AUV) engineering-quality data is providing opportunities to ensure that development plans are not exposed to unnecessary, avoidable geohazard risks. A key element of the multidisciplinary team approach is the application of integrated geophysical, geotechnical and engineering geomorphological methods that make best use of the high-resolution data these state-of-the-art technologies provide.

The integrated approach is providing valuable in guiding BP's offshore development plans towards properly identifying the geohazard risks and accounting for decision-making at all stages of the project programme (see companion paper by Evans et al. 1). The product of the geohazard assessment work underpin strategies for the optimization of field architecture (avoidance of geohazards) and the evaluation of cost effective options for geohazard-tolerant equipment design and protection (geohazard-resistant design).

West Nile Delta Gas Developments

The Nile Delta is one of the world's largest deltas, with a submarine fan of about 100 000km2 extending northwards into the Mediterranean Sea (Figure 1), and is a major area of hydrocarbon exploration. The delta extends 20–40km offshore to a shelf break where the water depth is about 100m; the maximum water depth beyond the delta slope is about 1500m. BP Egypt, together with partners RWE-Dea and Egyptian Natural Gas Holding Company (EGAS), intend to develop several offshore fields within the West Nile Delta (WND).

The modern Nile Valley is thought to have formed during the late Miocene at the same time as a major desiccation of the Mediterranean Basin. The salt deposits formed at this time were progressively covered by deep sea fan sediments discharged from the River Nile throughout the Pliocene and particularly during the Quaternary2. The WND has been subject to cycles of rapid sediment deposition, erosion and episodic submarine landslide activity for at least the last 250 000 years2.

The resulting present-day seafloor is an irregular patchwork of geomorphological forms and geohazard features including incised canyons, plateaux and escarpments, fault scarps, pockmarks and landslide scars (Figure 2). The shallow soils across the WND are predominately soft marine clays of terrigenous origins and hemipelagic clays. The mechanical properties of these soils are strongly influenced by their depositional histories and most significantly by post-sedimentation events and processes such as landslides, debris flows, turbidity currents and fluid expulsion.

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