Subsea oil fields account for around 30% of the total global oil production but keeping the oil flowing from fields in remote deep-water locations is no small challenge for operators. Teams of engineers both onshore and offshore work around the clock, 365 days a year to maintain the integrity of the subsea infrastructure that our energy-hungry societies depend on. As consumers in the 21st century we rightly expect them to perform all this without harm to people or the environment.
The modern subsea oil and gas field is a complex array of hardware, often distributed over an area of the seabed larger than the city of London, all connected by electro-hydraulic umbilicals - the lifelines of the operation. Even with dual redundancy built into these systems and the use of state-of-the-art components, materials and construction methods, umbilical failures have a huge impact on production from subsea fields. So, when an electrical fault develops somewhere in the system, the subsea engineers immediately start planning an intervention to answer the questions “Where is the fault?” and “How do we fix it?”
Planning an intervention efficiently and safely is always key to a successful outcome. The first question to be answered is the timeline – when does it have to take place? Some fault-finding operations have the luxury of being planned during annual maintenance schedules a year in advance, but more often interventions must be undertaken as soon as possible using a vessel of convenience. This can make the sourcing and logistics of equipment and personnel difficult. Specialised equipment may have to be transported from overseas by surface freight, and once in country may need to craned on board the vessel and secured to the deck.
Mobilising offshore crews has been made even harder this past year by the Covid-19 pandemic. With every country having their own Covid protocols in response to everchanging threat levels crews may be required to spend several days in quarantine both before and after the mission. This clearly drives up the costs and can limit the pool of qualified personnel willing to be away from home for so long.
Early on, C-Kore Systems recognised the difficulties subsea engineers have in locating electrical faults in their subsea umbilical networks. Their response was to develop a small, hand-held, testing device incorporating a wet-mate connector to test directly into the subsea equipment. This replaces the use of down-lines and topside testing equipment. A down-line is essentially a very long extension cord, hundreds and sometimes thousands of meters long that connects the subsea equipment to the testing equipment located on the deck of the service vessel. Being a small device packaged in a flight case, the C-Kore testing units are very easy to mobilise. They can quickly be sent to any location via airfreight, and can be walked on board the vessel, not requiring any specialised lifting equipment or sea fastening. Due to their size, they can even be helicoptered on board if the urgency of the job dictates.
The use of the C-Kore testing tools on offshore operations is allowing operators to complete their missions in less time and come back with better data and a clearer picture of what is happening on the seabed.
Earlier this year a major operator in the far east approached C-Kore asking for assistance in locating the source of low insulation resistance (IR) in their subsea electrical network. The low IR was posing a serious threat to the production of oil from the subsea wells. The customer’s previous experience of electrical fault-finding on the seabed had involved the use of a down-line test cable from a surface vessel; a process that requires the mobilisation of a heavy reeler unit and specialist technicians to the intervention vessel. Reliance on downline intervention limits the accuracy of subsea fault-finding due to the distance between the tester and the equipment under test and to the environmental conditions on the deck of the vessel. It also requires the management of safety risks on the back deck and on the seabed associated with cable handling under challenging weather conditions and sea states.
The first task was to decide on the best set of tools for the job. Discussing the goals for the operation with the customer and evaluating the field layout, the C-Kore engineers recommended the Cable Monitor units and Subsea TDR units. The Cable Monitor unit measures the insulation resistance (IR) and continuity of the electrical lines. The unit plugs directly into the equipment subsea to identify which lines have low IR values. Working at a very low voltage, the units safely test directly into Subsea Control Modules containing sensitive electronic equipment without any danger of damage. Divers can also work in proximity to the Cable Monitor during use, and do not have to retreat to the diving bell as they must do with higher voltage testing systems. This saves valuable testing and diving time. The Subsea Time Domain Reflectometer (TDR) tool works like a radar but for electrical lines, sending an electrical pulse down the line and listening for the reflections. By interpreting these reflections the precise locations of faults and anomalies can be determined.
Due the age of the subsea hardware the customer’s engineering team did not have access to detailed dimensioned drawings or STEP files of the interface at the umbilical terminations, but a review of the General Arrangement drawings and video files suggested that adjacent steelwork might make the deployment of the standard C-Kore tool too close for comfort. Finding out the hard way that the test tool would not fit was clearly not an option, so C-Kore took advantage of the modular design of the tools to configure the units specifically for the job to avoid any chance of a clash.
C-Kore assisted the client in making the subsea fault-finding intervention as efficient as possible by minimising the number of disconnections, the time on the seabed, vessel movement and the period of power isolation. They also preprogrammed the units with a sequence of core to core and core to earth insulation resistance tests before the units left the factory. All the customer’s offshore team needed to do was to connect the tool to the subsea circuit and flash the ROV lights at it to initiate the test. With the test units pre-configured for immediate deployment no specialist offshore personnel were required to operate them. Training was delivered via an on-line interactive session, whilst the client’s team were in Covid quarantine, so that they were all fully confident with the tools prior to the mission.
As soon as test results were obtained they were relayed to C-Kore’s team in the UK where specialists were on standby on the same shift pattern as the client’s team to analyse the data and support decision making whilst the vessel was still on station. The C-Kore engineers drew on experience from hundreds of similar situations to assist the client in quickly identifying the faulty parts of the circuit. C-Kore has also amassed a wealth of knowledge in interpreting TDR traces to determine the precise location of the fault and whether it is a short circuit, open circuit, or water ingress problem. Working with C-Kore in this way enabled the operator to benefit from access to a team of experts who can peer review each other’s observations and conclusions in step with the offshore operation on the far side of the world. Achieving the same result using other means would have necessitated mobilising two specialist engineers from the UK (to cover day and night shifts) and adding nearly 30,000 air-miles to the project’s carbon footprint.
For their customer in the far east the use of C-Kore’s tools and onshore support service resulted in several electrical faults being identified quickly and efficiently. This was achieved with reduced environmental impact and less exposure of personnel to the Covid risk of international travel. Once Covid-19 is a thing of the past the advantages of C-Kore’s easy-to-use tooling, online training, and 24-hour expert support services will still be delivering savings and environmental gains to the subsea industry.
For further information on C-Kore’s innovative subsea testing technology, please contact them:
Web: www.c-kore.com
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Tel: +44 (0)1904 215161