Drilling innovations to simplify oil and gas exploration
When it comes to it, getting oil and gas out of the ground is pretty crude engineering. The industry has a reputation for slow innovation, which in a sector that is inherently conservative for reasons of safety is not entirely surprising. If you’re going to drill through rock to pump a liquid out of the ground (especially if that liquid is flammable and accompanied by an explosive gas) then tried-and-tested technology is probably the best way to go.
This, argues Shell’s head of wells R&D, Jan Brakel, leads to an interesting dichotomy. ‘We can fly aeroplanes with three hundred-plus people on board on full automatic over a distance of 5000 miles across the Atlantic ocean,’ he said, ‘but we cannot drill 5000 metres without continuous human intervention, using equipment that is still based on the basic design at inception.’
“We cannot drill 5000 metres without continuous human intervention, using equipment that is still based on the basic design
Jan Brakel, head of wells R&D, Shell
Automated drilling is one of the oil industry’s most important innovation targets. This is partly because of the increasing difficulty of finding new oil and gas reserves. The sources now being tapped, such as shale gas and coal-bed methane, require a very large number of wells — Shell estimates that it may need to drill up to 6000 wells per year, and this could mean it would have to spend half of its exploration and production budget on drilling and completing wells, compared with just under a third for more conventional exploration.
Automating the drilling process would be an obvious way to keep the costs under control, and also gets around a problem which many sectors of engineering are experiencing — a shortage of skills. Constructing a well system for unconventional gas requires directional drilling, and finding people who can do that is becoming difficult, as experienced drillers reach retirement age. Automated drilling, so the argument goes, would be faster, more efficient, and safer, as it reduces the number of workers on site.
Shell has developed an automated drilling system called SCADAdrill (SCADA being the acronym for supervisory control and data acquisition, a type of software used for automated factory and process control), and is a component of a new well manufacturing system that it is currently trialling in Europe and North America. Based around a central hub, the well manfacturing system uses three different types of drilling rigs mounted on trucks to construct the complex of wells needed to extract gas from shale or coal bed reserves. One rig drills the ‘top hole’, the vertical upper portion of the well through which gas is extracted. Two intermediate bores are then drilled, starting at an angle and proceeding horizontally to meet at the base of the top hole; these are used to dewater the rock and encourage the gas to flow. The third type of rig installs the tubing and downhole pumps needed to operate the well.
The SCADAdrill system is used on the horizontal dewatering bores. Through sensors mounted on the drillbit, the system monitors the trajectory of the drill and its performance as it travels through the site geology, and controls its path to ensure that it meets the top hole precisely.
Automating drilling takes in three stages of autonomy, according to Brakel. The first is to mechanise the drilling equipment, such as the machinery which connects lengths of drill pipe. The second is to monitor torque and weight on the drill bit, and control these parameters to achieve optimum rate of penetration and the route of the bore-hole. The third level is to automate the entire process, including the speed of the pumps controlling drilling mud; this level of automation could be incorporated into a ‘black-box’ system which could run Shell’s contract wells.
Shell is also developing a new type of casing tube to line wells, which would make the drilling process far simpler by allowing the entire well to be drilled with the same diameter.
Currently, wells are drilled using a stage by stage process. The initial bore is drilled down until the sides start to become unstable; any further down and they would start to collapse. At this point, the drill is stopped, the bore is lined with steel pipe, and the gap between the side of the bore and the outside of the pipe filled with grouting.
The next stage of the bore has to be inside this hole, so a smaller diameter drill bit is used; the drilling again continues until the hole is on the verge of collapsing, then it is lined. And the process continues, with the diameter of the bores reducing each time.
Shell’s innovation here is to develop an expandable casing, which would allow the end of each tube to be ‘flared out’ to that it fits over the end of the tube below it. This can be done using a grade of steel which stretches while still remaining within the strengh parameters needed to stabilise the bore, or by using a slotted tube — a pattern of slots are scored into the surface of the outside and inside of the tube, not penetrating the full thickness of the steel, but allowing the end of the tube to expand by stretching the thinner sections of steel left by the slots.
Shell’s experiments with expandable linings, carried out at its test drilling rig at Rijswijk near The Hague, have indicated that a lining can be stretched at a rate of about 30m per minute. This slows the drilling process down, but there’s a trade-off — narrower bores are quicker to drill. Overall, the time the well is non-productive would be reduced considerably.
This technique would have a number of advantages, Brakel said. First, it reduces the amount of energy needed to drill the bore; wider bores need more energy because they have to displace more material, so for a given depth of bore, less rock has to be removed. It also uses less steel, less cement grouting, and less drilling mud; as well as a smaller drilling rig.
It also allows greater depths to be achieved, he added. There is a limit to the width of bore which it’s practical to drill, which means that the conventional tapering bore hole technique can only go down a certain distance: the lowest bore has to have a certain diameter to work, so the number of sections of different diameters is fixed. With all the sections of bore the same diameter, this limit is removed and — in theory — the depth reachable is increased considerably.
Shell intends to use expandable linings in the field this year, on an offshore well in the Gulf of Mexico; here, it will be used to reach a previously-unreachable field. Future development will focus on reducing the cost of the tubes, as they currently use a rather exotic — and therefore pricey — steel alloy.