The flexible subsea drilling rig set to bring down the cost of oil exploration

Current fluctuations in oil prices have highlighted the key characteristic of the oil industry – it is expensive business. While we, as consumers, are benefitting from an easing in prices at the pump, and the knock-on effect of cheaper groceries in the shops, it is not too difficult to see the pendulum swing the other way - American's responding to their glut of shale oil by consuming more, and Middle Eastern producers protecting prices by cutting back on output. Along with the wider economic mayhem this all creates, it also does not make it easy for the oil and gas industry to maintain consistent development plans. That oil price pendulum swings a lot faster than the development cycle of new reserves and when prices are low it makes investment in exploration a delicate calculation. And without the exploration now, it could be that resources are thin on the ground in the future. What helps is the introduction of new techniques and technologies that can bring down the cost of this exploration. The main reason that this cost is currently so high, when we are talking about offshore resources, is that the traditional core item of equipment is a drill ship. The distance between the surface and the seabed, which can be several kilometres, needs to be added to the length of the actual drill hole when accommodating the necessary drilling rods. They are also required to be reasonably stable if drilling is to be both accurate and controlled. As a consequence drill ships tend to be very large and very expensive. Canyon Offshore has been taking its operations to the seabed for nearly two decades, principally for trenching operations and some other engineering services based around underwater remotely operated vehicles (ROVs). About five years ago it started looking at a project that became known as ROV Drill. The logic behind this is to take the portability and flexibility of an ROV into the subsea drilling environment. This fits the model for modern oil exploration according to Martin Griffiths, the senior software engineer for Metis Automation, who was involved in the ROV Drill project. "I suppose they are taking more speculative chances," said Griffiths. "Where in the past there might have been a dead certainty that there was oil somewhere, nowadays it is small, isolated drill sites all over the place and you need to able to move around quickly and easily between them." ROV Drill is actually moved around on a small DP vessel with an 'A' frame at the back. DP, dynamic positioning, is frequently used in exploration and research activities as it is equipped with the technology (e.g. sonar and radar) to ensure it can maintain position in heavy seas without the use of an anchor. Canyon developed the drill hardware with Cellula Robotics. There are two key parts to ROV drill – the drill and the robotic arm. This arm can select any one of up to 60 tools from a rack that is arranged in a semicircle around it. The arm takes a tool, positions it at the drill head and screws it on. There can be a variety of tools from drill bits, drill rods and casings for taking core samples. If the objective is to drill one long hole it could be that the tool racks are filled with 3m long drilling rods that will be used to build up the drill tool piece by piece. However, ROV Drill can be used for a number of separate drilling activities and can remain underwater for several shifts, or even a week or two. In this case, samples can be returned to the tool rack for storage until ROV Drill resurfaces. Alternatives to PLCs Without the need to retract the total drill for each bore, as is the case with a drill ship, the ROV Drill is far more nimble and time efficient. But such functionality requires a considerable degree of control and that caused Canyon to reappraise existing control methodology. The rest of the company's ROVs used PLCs, but with a view to changing the approach Canyon looked to Metis Automation, an NI Alliance member. Griffiths commented: "There are some quite complex control challenges on here. Subsea PLCs are proven and have quite a track record, but there are challenges on this that PLCs couldn't meet. You need to do a few things subsea. You need to do some really fast and accurate logging rates, so if you are taking load tests to prove to your customer that this is the place to construct [a production platform] you need to have really good evidence of that. The CompactRIO will let you have those flexible, sometimes fast sometimes slow, logging rates. You may be down there for weeks at a time when the logging rates might be slower, but sometimes you might want to speed that up." CompactRIO is a software configurable controller from National Instruments and it lies at the heart of the ROV Drill. "We have got some really critical control conditions going on down there," continued Griffiths, "so dive site to dive site we have got no idea what kind of conditions we are going to meet. Some places have extremely strong side currents, so we have to put a lot of effort into just controlling the stability of the drill. We have got several control loops running in parallel, some trying to keep it stable, some trying to move the arms, sometimes against really strong currents to move the drill bit back and forth." Accurate drill control However, the most critical function involves controlling the speed and force on the drill bit during a test – in some tests this force is the important parameter rather than taking samples. Griffiths continued: "CompactRIO allows you to assign higher priorities – so when we are drilling we might want to put all of our speed and all of our effort into controlling that drill, but when we are moving the arms we might want to slow down the drill control because it is at idle and move onto something else. That is something that the PLCs were not able to let us do, but the CompactRIO allows us to move around and completely change the configuration." An Ethernet expansion chassis is used to increase the number of inputs as there are over a hundred proximity switches, sensors, control valves and the like, but the single processor of the CompactRIO handles all the tasks. ROV Drill is connected to the surface by an umbilical – Ethernet over fibre optic – that carries all communications and power. On the support vessel is a control cabin from which the ROV pilots have access to video feeds and all information from the ROV Drill. "We have got some neat LabView interfaces here that show the position of the arms and the drill bit, and a huge amount of feedback. They just control everything from this control chair," concluded Griffiths. Two systems are currently in operation; one in the North Sea and the other currently deployed off West Africa.