The Usan development comprises 42 subsea wells: 23 oil producers and 19 water- and gas-injection wells. Subsea trees and manifolds are linked by production and injection flowlines, flexible risers and electro-hydraulic umbilicals to the FPSO. The architecture provides dedicated production gathering, water injection, gas injection, chemical delivery, control and monitoring across the seabed drill centres. The topsides separate oil, gas and produced water, stabilise the crude, compress associated gas and condition seawater for reservoir injection. An oil-and-water wash tank is incorporated within the hull, while dedicated produced-water treatment and seawater-injection systems support continuous processing and reservoir-pressure maintenance. Metering, chemical injection, subsea controls and flow-assurance systems support the well network. Permanent utilities include onboard electrical generation and distribution, flare and pressure-relief equipment, firewater, fire-and-gas detection, emergency shutdown, marine systems, cargo handling, telecommunications and accommodation. The purpose-built vessel is approximately 320 metres long, 61 metres wide and 32 metres deep, with storage for about two million barrels of crude. A permanent spread-mooring system holds the FPSO at a fixed heading. Stabilised oil is exported through a separate loading terminal comprising an offloading buoy and two offloading lines, allowing tankers to load clear of the FPSO. Associated gas is used for fuel or reinjected through the field’s gas-injection system; no permanent sales-gas export pipeline is documented for the original development.