Automated drilling is one of the oil industry’s most important innovation targets.
The sources now being tapped, such as shale gas and coal-bed methane, require a very large number of wells, and 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
Automated drilling would be faster, more efficient, and safer, as it reduces the number of workers on site.
In this R&D sector, Shell has developed an automated drilling system called SCADA drill (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 trialing in Europe and North America.
Based around a central hub, the well manufacturing 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 SCADA drill system is used on the horizontal dewatering bores.
Through sensors mounted on the drill bit, 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:
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.
The SCADA drill computer system connects to the existing instruments and controls of a drilling rig.
It can thus operate the rig machinery and monitor all aspects of the drilling process.
In fact, the monitored parameters serve as the feedback control for the rig machines. In this way the orientation of the borehole is constantly checked as it is being drilled, helping to ensure that the well is drilled efficiently and that it reaches its target.
Although it is capable of working without human supervision, SCADA drill allows well engineers to monitor the rig remotely. If necessary, control can be taken over from the machine.
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 is developing 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.
This technique would have a number of advantages:
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.