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This article, written by Technology Editor Dennis Denney, contains highlights of paper OTC 18655, "Erha and Erha North Development: Overview," by T.C. Parker and A. Sofidiya, SPE, ExxonMobil, prepared for the 2007 Offshore Technology Conference, Houston, 30 April-3 May.
In March 2006, ExxonMobil affiliate Esso E&P Nigeria started production from the Erha deepwater development approximately 97 km offshore Nigeria in 1200 m of water. The Erha development includes Erha North, a satellite development that came on stream in September 2006. The Erha and Erha North Project consists of 32 subsea wells tied back to a floating production, storage, and offloading (FPSO) vessel. A catenary-anchor-leg-mooring (CALM) buoy is used for crude-carrier docking and product transfer.
The first exploration well, Bosi-1, was drilled on the block in 1996. The Erha oil discovery was made with the Erha-1 well in February 1999. Appraisal well Erha-2 was completed in November 1999, and the Erha-3 appraisal well and sidetrack were completed in September 2001. Well Bosi-2 discovered oil in March 2002. After the start of Erha development drilling, an oil discovery was made in March 2004 with Well Erha-7 and Erha-7 sidetrack, leading to the addition of a third drill center, Drill Center North (DCN). Recoverable reserves are estimated to exceed 7.9×107 m3 of oil.
The Erha and Erha North plan included sequential startup of three drill centers, managed simultaneously with a two-rig development-drilling program and ongoing production operations. The subsea wells are connected to a new-build, spread-moored FPSO through flowlines and steel catenary risers (SCRs). Processing facilities installed on the FPSO handle 3.3×104 m3/d of oil, as well as provide injection capability for 2.4×104 m3/d of water and 9.6×106 std m3/d of gas. Processed crude oil is stored in the FPSO and periodically offloaded to trading tankers through a CALM offloading buoy.
Initial development plans focused on selecting a development concept for the Erha field N4 resource with flexibility to accommodate future tiebacks to commercialize additional discoveries on the block. The development concept captured and incorporated learnings from ExxonMobil’s worldwide project execution, with particular emphasis on other west Africa projects, technology, and operability.
The original Erha full-field development plan included 24 subsea wells, clustered in two drill centers: Drill Center East (DCE) and Drill Center West (DCW). All subsea wells would be drilled and completed from a mobile offshore drilling unit (MODU) and tied back to the FPSO. Producing wells would be brought together through manifolds with insulated flowlines and risers connecting the manifolds to the FPSO. All gas-injection wells would be over the gas cap from DCE, and water-injection wells would be from DCW. Injection wells at each drill center would be routed through a manifold connected to the FPSO with a single uninsulated flowline and riser.