Through field testing offshore Angola, Cabinda Gulf Oil Ltd. (affiliate of Chevron) and US-based Natural Gas Turbine Technologies Inc. (NGTT) have developed a natural gas powered turbo-electric generator that will be installed at each of company’s locations in Angola where gas lift is available.
The new product is the result of Chevron’s search for a more robust, more reliable source of remote power for its gas lift control valves and SCADA equipment at its offshore and onshore operations in Angola.
Photo of the GT-400 gas-powered turbo-electric generator on the Cabinda Gulf Oil Ltd.-operated Wamba-Bravo platform on the Takula field in block O offshore Angola.
In 2004, NGTT delivered a 150 W prototype turbo-electric generator for testing on a Chevron platform in the Takola field offshore Angola. The unit was identical to NGTT’s GT-150, except the housing was electroless nickel-plated inside and out, it was rated for an operating pressure of 1,800 psi rather than 600 psi, and the internal electrical components were epoxy encapsulated to withstand wet sour gas.
The prototype was installed in late 2004 on the field. With the exception of a few problems with the electronic battery charger, but unrelated to the operation of the turbo-electric generator itself, the prototype ran for about one full year before being taken out of service for disassembly and inspection. The unit showed almost no signs of wear. It had held up against the wet gas going through it and had demonstrated to Chevron’s satisfaction that NGTT technology could operate successfully in harsh environments flowing wet gas.
As a result, Chevron and NGTT settled on a new production unit specification. The new unit, GT-400, was to deliver 400 W rather than 150 W of power using substantially the same amount of gas flow as the prototype. It was to be rated at 1,800 psi operating pressure and be FM-approved for Class 1, Division II locations. The electronic control was to be able to run 24 V DC equipment directly and charge backup batteries at the same time. In addition, the electronic control was to have reporting capabilities using Modbus protocol and be capable of being shut down remotely. In 2005, Chevron ordered 10 of the units.
NGTT delivered the units in July 2006. The first was installed on Chevron’s Wamba-Bravo platform on the Takula field offshore Angola in November 2006. The unit takes gas from a 910 psi, 19-mm (3⁄4-in.) lift line. After turning the turbo-rotor flywheel and generating the required electricity, the gas is returned to a 180 psi oil production line. It is estimated 57.6 Mcf/d passes through the generator to provide enough DC power to run 14 Flowserve Valtek StarPac control valves and a PLC while keeping 16, 12 V backup batteries charged - equivalent to 12 amps at 24 V DC.
Chevron plans to install two GT-400s at each of its locations in Angola where gas lift is available. One unit will be the primary generator and the other will serve as backup.
