Phase 1 consists of a single subsea well tied back to the platform by means of an 8-in. production line, a 4-in. gas lift line, and a control umbilical. The second phase involves a second well, drilled around 100 meters from the first one, with a choke manifold tying in production from the two wells.
ECA's TOV control system is part of the second phase and includes two control units for Argo 1 and Argo 2 (the former replacing an existing control unit). In addition, it is supplying a control unit or the choke manifold and also a surface-based unit. The complete control system has been delivered for integration with Xmas trees in just seven months.
TOV technology relies on small electro-hydraulic control modules, each able to control one hydraulic valve and also to acquire data from two external sensors. Each module is connected on a dedicated panel which remains part of the Xmas tree or manifold structure, and is hard-piped to the actuators, wired to the sensors.
All the modules are connected to an 'electro-hydraulic bus,' which is a prolongation of the umbilical. The low weight (22 kg) of the modules, coupled with their 2,000 meters water depth capability rating, also makes the TOV principle adaptable to deepwater fields, ECA points out, allowing easy retrieval or installation by ROVs.
The Argo 1 and 2 wells are nearly identical as far as the control system is concerned. Only the external sensors are different, Argo 2 being equipped with dual P/T sensors while Argo 1 has just one P and one T sensor. Both feature four 2-in. actuators, one 4-in. actuators, and one safety valve. Gate valves are controlled by 3,000-psi, water-based fluid, with the safety valve controlled at a level of 4,000 psi. Each well is also equipped with a panel including six TOV modules, a 241 accumulator for the gate valves and a 51 accumulator for the safety valves.
The choke manifold includes two 2-in. chokes for gas lift and two 4-in. chokes for production. Each choke is controlled by two monostable TOV modules organized on an eight-slot panel. Three pressure sensors, three dual pressure/temperature sensors and four choke position sensors are also employed by the TOV system.
In accordance with the TOV principle, the three panels are linked as a daisy chain, each module being connected to the common trunkline. Communication on the 13 km umbilical is organized in a master/slave mode with the surface unit. Two operator levels are available with passwords, allowing the supervisor to change some parameters in the subsea modules by a simple downloading action. Data and controls are both displayed at the Hidra platform and at the Rio Cullen centre onshore, through a telemetry link.
Despite Argo's shallow water depth, TOV has adapted well to this project, claims ECA, due to its modularity and the step by step installation.
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