Case 6 New Gas Reservoir Production with Offshore Oil Site

CASE 6 NEW GAS RESERVOIR PRODUCTION WITH OFFSHORE OIL SITE 

Since going online in 1993, the joint venture has reaped large dividends from the P15/P18 blocks of Holland s Rijn field, some 40 km (25 miles) from Rotterdam. BP-Amoco processes 13 MMm (500 MMft ) of natural gas from the field each day also, nearly 2,000 m (12,300 bbl) of condensate are produced daily. The project marks the first time Dutch gas has been produced to sales specification at an offshore location. Seven reservoirs, developed separately, are tied back 

To meet sales specifications, gas produced at the wellheads must be free of water and hydrocarbon liquids. Twin turboexpanders are a key component in this process, providing dewpoint control with optimal efficiency. Initial processing takes place at the wellhead platforms, where methanol is injected to inhibit hydrate formation. A corrosion inhibitor is also added to prevent gas from damaging downstream equipment. 

At the central platform, water and hydrocarbon liquids are first removed in knockout drums. Then saturated natural gas, free of any liquid droplets, enters the twin expanders. The gas is cooled below its dewpoint, allowing heavy hydrocarbon components and water vapor to condense in the discharge stream. Turboexpanders were chosen for two main reasons They are more compact than competing methods of controlling the dewpoint and their operating costs are typically lower than those of many alternatives. 

The expanders also remove energy from the gas, using that energy to drive a centrifugal compressor for pipeline recompression. As gas expands through the expander s inlet nozzle, pressure drops from 90 bar (1,300 psig) to 55 bar (800 psig). Temperature drops as well, below the dewpoint, and the liquids formed can be separated from the main gas stream. 

---