02 December 2008
Bosch Rexroth was subsequently selected to provide PLC-based control.
While drilling into the sea bed, the bore hole may pass through several different strata, each layer having its own particular characteristics. If the well is not cemented correctly, then the contents of the various layers can mix and cause problems with the well and result in expensive downtime.
Two diesel engine driven pumps are used to push the cement down the well; these sit in the Cement Room usually placed in the bowels of the rig. After the cement has hardened properly, it is drilled through and deeper drilling of the well recommences. Because of the low pressures involved, the operator can control the pumps manually in relative safety.
These two pumps lend themselves to a variety of other pumping operations, such as pushing chemicals into the bore hole to permeate the formation and thereby enhance recovery. Again, since the pressures are relatively low, the operator can control the diesel engine driven pumps from the local position at the engines.
For high pressure testing operations, these same two pumps are used to force water into the bore hole to test the well. These operations are more hazardous and require the pump operator to stand in a place of safety, away from the Cement room. Under these circumstances, a remote control system is necessary.
Aberdeen Control specialises in the manufacture and provisions of hazardous area equipment for the offshore oil, gas and petrochemical industries and constructs a control cabinet, designed to allow remote control of these diesel engine driven pumps.
It was nine of these cabinets that Schlumberger requested as its existing electro-pneumatic fully-remote control system, whilst adequate, did not provide a fine enough control for some functions.
Aberdeen Control managing director, Graeme Craig, was asked to assess if this type of remote control system could be achieved and turned to Bosch Rexroth.
At the initial project consultation with Aberdeen Control and Schlumberger, Bosch Rexroth proposed using a PLC to control the DDL fieldbus LP04 manifold to ensure that the hazardous zone certification requirements were met. In addition to providing a cost-effective solution, the expectation of using a PLC-based solution was to achieve finer control of the system. The technical aspects of implementing a PLC-based control system into the design were examined with the Aberdeen Control project team at a subsequent onsite meeting.
The resulting design solution included Rexroth’s LP04 double 3/2 version valve manifold with integrated DLL field bus and RA14 3/2 valves. For the safe area version, Rexroth’s ED05 pressure regulator and DDL and ED05 sub-base were specified, along with filter assemblies, mounting kit and DDL units and ancillary components. The ED05 products were swapped for ED07 products for the ex-rated system.
On the control side, Rexroth’s mini-PLC, the IndraControl L20, was used with IndraLogic firmware. The customised program was developed by Rexroth’s application engineers using the system tool IndraWorks with WinStudio lite runtime and editor.
‘Prior to shipment to the oilrigs, the modified control systems were bench tested and then connected to a diesel engine driven pump for full cycling tests,’ explained Craig. The control cabinets are installed and operational on two oil rigs, Rowan Gorilla VI and Leiv Eriksson.
‘Overall this project was very challenging,’ concluded Craig. ‘In the end it worked out rather well and both Schlumberger and Aberdeen Control have been pleased with the technical design.’
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