Sand Exclusion and Management in the Okwori Subsea Oil Field, Nigeria
- Frederic J.-B. Guinot (Addax Petroleum Corporation) | Jim Duncan (Hess Thailand) | Stuart Douglass (M-I Drilling Fluids UK Ltd.) | Martin J. Orrell (Addax Petroleum Corporation) | Bruno A. Stenger (Abu Dhabi Co. Onshore Oil Opn.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- March 2009
- Document Type
- Journal Paper
- 157 - 168
- 2009. Society of Petroleum Engineers
- 1.14 Casing and Cementing, 4.1.2 Separation and Treating, 4.5.3 Floating Production Systems, 2.4.3 Sand/Solids Control, 3.2.5 Produced Sand / Solids Management and Control, 5.1.1 Exploration, Development, Structural Geology, 4.1.5 Processing Equipment, 2 Well Completion, 1.8 Formation Damage, 7.1.9 Project Economic Analysis, 5.1.2 Faults and Fracture Characterisation, 5.6.4 Drillstem/Well Testing, 1.6 Drilling Operations, 1.2.3 Rock properties, 4.2.3 Materials and Corrosion, 4.2 Pipelines, Flowlines and Risers, 2.4.5 Gravel pack design & evaluation, 4.5 Offshore Facilities and Subsea Systems, 1.11 Drilling Fluids and Materials, 1.5 Drill Bits, 5.2.1 Phase Behavior and PVT Measurements, 2.2.2 Perforating, 1.10 Drilling Equipment, 7.1.10 Field Economic Analysis, 1.2.1 Wellbore integrity
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Several downhole-sand-control failures in Okwori subsea oil producers triggered a significant overhaul of the downhole-sand-control method and a review of topside sand management. Because the eventuality of further downhole-sand-control failures in existing producers could not be ignored, a surface-sand-handling and -management facility was designed. For the future development producers, the downhole-sand-control method was re-engineered to increase its reliability. The initial multizone, fully selective sand-control-completion system, with expanded sand screens inside the casing, was abandoned. A revised openhole sand control was designed with similar completion selectivity. The new completion system implied a change in drilling practices, in reservoir drill-in fluid, and in filter-cake-cleanup techniques that required simultaneous engineering. These revisions were validated and implemented only a few months after encountering the first major sand-control failure. The Okwori floating production, storage, and offloading (FPSO) vessel was not expected to deal with sand production. Temporary sand traps were installed to minimize production downtime and to determine flow regimes that minimized sand production. Severe-service adjustable chokes were introduced to avoid valve erosion and stabilize production rates. Finally, a long-term topside-sand-management solution was designed and recommended for implementation.
With a rig-intervention cost of USD several million and high initial capital expenditure in the range of USD 25 to 35 million, Okwori subsea-development producers were designed to be "interventionless" as defined in Powers et al. (2006). Because of the very high capital expenditure, each Okwori completion must access enough reserves to minimize payback duration and optimize net present value. In the stacked and compartmentalized Okwori reservoirs (Figs. 1 and 2), accessing sufficient reserves per completion required carefully crafted well trajectories penetrating multiple targets like "beads threaded on a necklace." Because selective production from different reservoirs and sand exclusion were mandatory, the Okwori producers required a combination of expensive downhole equipment. "Murphy's law" stands as a warning that the more equipment run in a hole, the more that can and will go wrong. The quest for interventionless Okwori wells translated, therefore, into a risk-minimizing search based on best-engineering practices, proven technologies, and best-implementation practices, with the additional constraint of challenging project economics. Risks that could affect the project adversely were mitigated, and technical solutions were selected so that the project would remain economical throughout its life. Early downhole-sand-control failure on two Okwori producers during the first stage of the development phase prompted the producer and service companies alike to tackle these issues within a very tight schedule.
|File Size||3 MB||Number of Pages||12|
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