Who Dat Project - Deepwater Subsea Production of Light and Heavy Oil
- Dennis Denney (JPT Senior Technology Editor)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- May 2013
- Document Type
- Journal Paper
- 106 - 111
- 2013. Offshore Technology Conference
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- 81 since 2007
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This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper OTC 23378, "Subsea Who Dat Project—Producing Light and Heavy Oil in a Deepwater Subsea Development," by Gerard J. Simms, SPE, Bruce Cooley, SPE, and Rick Fowler, SPE, LLOG Exploration; Kosta J. Leontaritis, SPE, AsphWax; and Kana Krishnathasan, SPE, Intecsea, prepared for the 2012 Offshore Technology Conference, Houston, 30 April-3 May. The paper has not been peer reviewed.
Plans were developed to produce multiple deepwater reservoirs with vastly different fluid properties from a subsea development in 3,100 ft of water in the Gulf of Mexico. Diagnostic and flow-assurance (FA) testing of the different-density oils addressed viscosity including non-Newtonian, wax, asphaltene, and hydrate behavior; downhole and flowline commingling; and fluid-compatibility tests. Provisions for pigging and a chemical-treatment program were added for extra assurance. A larger-sized oil-export line was selected to allow sufficient capacity for blended or heavy oils after restart.
The Who Dat field is in the Mississippi Canyon protraction area of the Gulf of Mexico and is being developed with the Opti-Ex semisubmersible floating production system (FPS), which has a capacity of 60,000 BOPD and 150 MMcf/D of gas. The field primarily contains oil and consists of ten stacked amplitude- supported reservoirs in a salt-withdrawal minibasin. Three wells had been drilled at the time this paper was written, penetrating more than 700 ft of net pay in nine distinct reservoirs ranging in depth from 12,000- to 17,000-ft true vertical depth. Both gas and oil reservoirs were found, with varying fluid properties. Significant fluid data were acquired in the openhole program, with more than 60 downhole fluid samples. Twelve full pressure/volume/temperature (PVT) studies and eight diagnostic FA studies were performed to gain an early understanding of the fluid. Later, flowback oil samples were acquired, rechecked, and evaluated further.
Field development includes 12 subsea wells (i.e., wet trees) flowing into three four-slot subsea manifolds. Drill Center A has one manifold, and Drill Center E has two manifolds. Each manifold is connected to the FPS with dual 6-in.-nominal-diameter wet-insulated flowlines and flexible risers having the capacity of roundtrip pigging. These infield flowlines are approximately 3 miles long, and the seafloor geometry results in a downsloping flowpath. The project includes a 10-in. gas-export line and a 14-in. oil-export line, also with flexible risers. Fig. 1 shows the subsea layout.
The key inputs for the FA process are uncontaminated fluid samples and detailed laboratory analysis. In the case of system selection for the Who Dat field, fluid samples were available from three wells and multiple formations. There were uncertainties about key formation-fluid properties resulting from drilling-fluid contamination, including viscosity, foaming, and wax content.
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