by Peter Kuusimaa, Owner of Comet Tech
I have decided to write this article since electric control in drilling rigs and particularly in exploration rigs is often regarded as unreliable and too complicated. However, more manufacturers already have electrical control options as well as HMI (human-machine interface = display) in their fleets to give more accurate information of the drilling process and parameters, as well as the option to log drilling parameters on the go.
Then why do electronics have such a bad reputation amongst drillers and drilling companies? I can name a couple of things from my experience, and I am sure you can think of a few more. Before, the biggest issue was to find components that are protected against the elements, since usually exploration rigs won’t have a driller’s cabin or any other safe place where they could be placed.
Programmable logic controllers (PLCs), for example, which are meant for factory automation, need to operate in an air-conditioned enclosure. With water, grease, temperature fluctuations, etc. being a constant part of drilling, a PLC won’t last very long in a rig. Since it is mandatory for the components to have a good enough IP rating, they tolerate extremely high and in some cases low temperatures as well vibration. The second issue is troubleshooting. If something does not work, you only need a spanner to crack the hose and see if that practical actuator or valve gets oil from the system. In electrical systems, particularly in CAN bus ones, troubleshooting can be more difficult depending on how the system is designed. Not to mention that you need at least a good quality multimeter and basic knowledge of the system itself to troubleshoot. The old maxim that electricity is blue, and it hurts isn’t enough anymore.
I have been fortunate to be part of the change in the drilling industry from the early 2000s when I was working as a young design engineer and I got to clearly see the benefits of electrics and CAN. I have also seen firsthand some issues they have caused. I have prepared three examples (see Examples 1-3) from a practical point of view of different kinds of controls without getting too deep into the topic.
These examples are manually/direct-controlled mobile valve, pilot hydraulic-controlled mobile valve and electrically controlled hydraulic mobile valve. It is also good to remember that hydraulic pressure generates a force which is moving the spool in both hydraulic- and electric controlled valves, excluding valves meant for lower flow rates.
Examples 2 and 3 increase the flexibility to locate controls to an ideal place for the operator without moving the main valve and large amount of hosing with it. Example 3 is especially more flexible since valve is controlled by electrical joystick, so no hoses or any type of hydraulic valves are close to the operator. This type of system is very convenient to use and safer than the other two, as there is no possibility of a high-pressure oil injection, there is less noise and less heat.
So why do we need CAN bus systems if electrical control is just as convenient and safe? I believe the following systems (see Examples 4 and 5) are the best example to show the benefits of CAN bus.
Let’s say we have four-spool mobile control valve, which has two PWM (pulse width modulation) controlled solenoids per each spool. So, we need a total of 8 wires from the spool to the control unit, which supplies control signal to the solenoids. The same control unit is also connected to joysticks which are normally either hall sensor or potentiometer type. Usually, the control unit is located close to the joysticks because the signal they supply is more sensitive to interference and its level is lower than the control signal to coils. In that type of system, we already have 8 individual wires which can be damaged. Not to mention that the wires must be big enough to be able to transmit control current, so we are talking about a rather large bundle. Also, the more valves you need to control, the more wires you will need.
If instead of ‘normal’ PWM coils, we use coils with CAN receivers in directional control valves, here’s how the system would work (see Example 5).
We have CAN bus system, so we only need two CAN wires between the control unit and coils. Those wires are only transmitting low level voltage signal between the control units, which means that wires don’t need to have a large cross section. Instead of eight possible points of malfunction, in this system we only have two. If for example we have 20 valves, the benefits of this kind of system are undeniable compared to the previous system with only one control unit. Admittedly, we still need operating voltage and ground to every coil, but still, the number of needed wires is lower compared to the system from the previous example.
Now that we have established the benefits of the system where control signals can be multiplexed between control units, like CAN bus, let’s think about the other benefits of the electrical control system. For example, we have a cage around the mast, which protects the driller from rotating parts and there is a door in the cage (see Example 6). If the cage’s door is open, the rotary head can’t be activated or can be rotated at a really slow speed.
Let’s now use the systems from the previous examples: direct/manual-controlled hydraulic, hydraulic pilot control and electrical control. In direct/manual-controlled systems we need to direct the rotation oil flow from the control valve first to a valve in the cage which then would allow oil flow to rotate the head motors in case the cage is closed. In this kind of system, hoses must be big enough to minimize flow losses and should also be able to withstand the maximum system pressure.
The valve which senses if the door is closed or open must be as large for the same reason and it will need a lot of force to operate due to its sheer size. This kind of system is not only difficult to make but also increases loses in the system because of the long hose runs. In a hydraulic pilot-operated systems (see Example 7), stopping or slowing the rotation can be done in two ways.
We could use a system similar to the one described above or place the valving in a pilot circuit. When the valving is placed in a pilot circuit, there are the following benefits: the sensing valve for the cage door does not need to be large, it does not need to withstand the maximum operating pressure of the hydraulic system and it can be activated with less force. Also, it is more convenient for the driller to operate a hydraulic joystick compared to a direct-operated valve. However, if we instead have one or several valves which can rotation interlock, the system becomes more complex, and more hosing is needed. Also, long pilot lines sometimes result in delay in control and the system becomes awkward to operate.
If using electrics, the simplest solution would be to use a proximity switch, a relay and a solenoid valve (see Example 8).
By doing so, long hose runs can be replaced by a proximity switch and wiring, which controls the interlock valve. Options for component location are many, but I believe that everyone agrees that running two core cable is in most cases easier than hydraulic hoses and takes up less space. Also, if one solenoid valve is close to another, the valves system has minimal delay. Again, thinking of a more complex system with multiple functions which can interlock rotation, this one will become complex and difficult to troubleshoot due to the many interlocks. But if instead of using relays with proximity switches, we had a PLC where all proximity switches are connected – which can be more expensive, however – there are undeniable benefits. Some of them: the system is more reliable as PLC does not have mechanical contacts as relays do, the status of proximity switches can be monitored, so cable breakage can be detected, more complex interlocking can be done via the PLC software and its characteristics can be easily altered without doing any physical changes to the system. When the system has an HMI, the operator gets real time information of different interlock statuses and whole system diagnostics.
I hope this article was able to point out some benefits of using electrics in drilling rigs. However, the most important thing to consider when deciding between hydraulic and electric controls is the level of technical expertise of the people who will maintain the systems and equipment available. Even the most advanced PLC-controlled system is useless if no one knows how to fix it or has any troubleshooting equipment when a problem arises.
About the author
Peter Kuusimaa is a Finnish mechanical engineer who has been working with and designing hydraulic and control systems for drilling rigs for over 20 years and in different continents. He is currently based and works in Australia. He has been part of many major drilling companies, nowadays he works as a consultant and a freelancer. You can find Peter at Comet-Tech Pty Ltd, on www.comet-tech.com.au or at comet-tech@bigpond.com.
