The extreme pressures and volatile environments in oil & gas require all that hydraulics has to offer — precise control and safety at high pressures.
By Josh Cosford, Contributing Editor
I love the town of Ithaca in upstate New York. We discovered it years ago in a casual drive in and around the Finger Lakes. We stayed in a recently renovated boutique hotel called Argos Inn and explored the town the following day. After the requisite coffee shop waylays, our walk led serendipitously to a large, flowing stream descending a gorge. Curiosity led us up what seemed like a never-ending, yet breathtaking, climb up what we later discovered was Cascadilla Gorge Trail.
After reaching the trail’s summit, we recognized while catching our breath that we stood at the entrance to Cornell University. I’m generally not geographically challenged, but it came as a complete surprise that Cornell was in Ithaca. Regardless, the exploration continued (partially for the caffeine refill). Our walk led through the legal library and saw us exit across from the Hollister Hall School of Civil and Environmental Engineering. A large circular sign outside a basement window caught my attention — “DeFrees Hydraulics Lab.”
My interest was piqued; we crossed the street and entered the building to scope out what was clearly my undiscovered fluid power mecca. There hung various student projects and displays in the hallways, and after digesting their content, my enthusiasm faded. Indeed, I discovered the other hydraulics — sure, kind of cool, but akin to telling your teenager their sweet sixteen gift is a car only to unwrap a Ferrari Lego set.
As we fluid power professionals define it, hydraulics is the controlled transfer of work. A hydraulic pump converts incoming mechanical energy from a prime mover (usually a gas engine or electric motor) into hydraulic energy manifesting as both pressure and flow. That hydraulic energy will flow through various control and distribution components on their way to downstream actuators such as cylinders and motors. Anything from log splitters to injection molding machines employ hydrostatic energy to perform high-power functions.
On the other hand, the other hydraulics describes the control and conveyance of groundwater, such as in or through rivers, streams, oceans and lakes. Hydraulic engineers also design stormwater systems to prevent local flooding while sometimes intercepting and directing such waters for purposes such as irrigation.
Hydraulic fracturing — extreme pressures and flows
Furthermore, there exists a form of hydraulics splitting the two above concepts — hydraulic fracturing. Hydraulic fracking, as it’s more colloquially known, is a process where oil and gas are extracted using specialized, pressurized fluids pumped deep underground. Fracking itself is indeed a hydrostatic effort since pressurized fluid works to crack and create fissures deep underground where oil and/or gas may break free from its longtime prison.
Just as with traditional hydraulics, the source of high-pressure fluid begins at the pump, where incoming mechanical energy is converted from the mechanical energy of the prime mover — in this case, almost exclusively from a diesel engine. Indeed, the input of power used for fracturing exceeds even the most potent hydraulic power units — think upwards of 5,000 hp or more.
The very large volume positive-displacement piston pumps work at around 15,000 psi or more and must be capable of withstanding acidic and abrasive fluids. In fact, the pumps are required to resist sand contained within the slick water. If you know anything about hydraulic fluid conditioning, you know how damaging particulate is to hydraulic pumps. Color me impressed with a frack pump’s contamination resistance.
You’d guess correctly that fracking operations require barrels of flow. No kidding, many oilfield engineers literally describe the flow requirements for the various fracking stages in barrels per minute. In perspective, 42 US gallons constitute a single barrel of oil, so imagine when the process describes 90 barrels per minute. Such a combination of high pressure and flow easily elucidates the requirement for thousands of horsepower. The frack sites combine a dozen or more pumps to achieve such flow (especially because few pumps are as large as my first example).
So without getting into too much detail, because this is a fluid power publication, after all, I’ll explain how fracturing works. A rig drills down thousands of feet into ancient shale before the wellbore drills sideways from its kickoff point for thousands of feet longer. The team inserts a tube before pumping in concrete to seal the bore. Then, explosive charges are inserted deep down the wellbore, where their explosions rupture not only the steel and concrete tube but also the surrounding shale.
The frack pumps send slick water down the wellbore where the ultra-high pressure further fractures the shale to open up channels of flow where oil and/or gas may leach out. The fracturing process occurs many more times to create thousands of fissures hundreds of feet deep in all directions into the shale. After all fracturing is complete, the decades-long process of pumping oil and/or gas from the well may begin.
Traditional hydraulics at play
Our hydraulics serve the oil & gas industry in various capacities, of course. In fact, you may be surprised to learn that the oil & gas industry employs one of the most sophisticated hydraulic machines on the market — the seismic vibrator. These impressive machines are a piece of the reflection seismology puzzle, which uses low-frequency vibrations much like sonar to reflect off geological formations deep underground. Geophone sensors strategically positioned a distance away from the vibrator will pick up the sonic reflections, and software interprets the information to essentially map the geophysical nature of the Earth below.
The intense vibrations emit from a large oscillating plate whose mass may exceed five tons. Combined with the truck’s weight and force of the cylinders, high inertia is imparted by sophisticated closed-loop hydraulics. Pilot-operated servo valves transmit precisely administered pump and accumulator flow to vibrate any frequency up to 250 Hz or more.
Closed-circuit feedback compares the LDT signal in the cylinders to the desired position and velocity of the electronic control system to offer a precise and repeatable frequency response of the vibrator. With high-powered servovalves comes all the gratuitous accoutrement required to support them — high-pressure pumps, ultra-fine filtration, accumulators and machine controllers.
Servo-controlled high-pressure, closed-loop piston pumps are standard for these applications. In addition, the closed-loop pump design offers flow to the wheel drive motors for vehicle traverse to relocate to new work locations. Servovalves operate best with high yet stable pressure drop, so a servo-controlled pump with its own closed-loop pressure and flow control offers the most precise pump option available.
As you may or may not know, servovalves are the most sensitive hydraulic component to contamination’s damaging effects. Moreover, a system running at higher pressure may experience more wear or damage because particles are forced through clearances or orifices with more force. Expect to see only highly efficient 3-micron filters every step of the way on seismic vibrators.
Servovalves offer greater precision when they run with higher pressure drop. In other words, when there is difference between the pump port and work port pressure in a servovalve, the higher it flows and the more accurately it performs. However, pressure drop anywhere in a hydraulic system results in pure heat equal to the product of flow and pressure differential. Running closed-loop hydraulics also leaves little room for excess heat, so seismic vibrators come equipped with massive liquid-to-air coolers (likely run from a thermostatically controlled hydraulic fan).
Hydraulics — the power behind oil & gas development
Hydraulics in oil & gas extraction is not limited to the exploration side of the coin. Once the well location is finalized, the site must be cleared and prepped to provide an appropriate area for the well pad, drill rig, centrifuge and generous storage. All that construction work requires construction equipment, and construction equipment requires hydraulics. There isn’t enough room to explain the operation of excavators, graders, dump trucks and dozers, but they are nearly exclusively fluid powered.
A drill rig, for example, may also equip one of various hydraulically operated components. The snubbing rig offers a method of adding or removing pipe sections while the well remains under pressure, a process that improves efficiency. For example, to remove pipes, the sections are first clamped firmly by slips, which are essentially powerful hydraulic collets. Snubber cylinders then jack the pipe to remove sections before they are set aside, and the process is repeated.
As the pipe sections are jacked up, well pressure must be controlled. Blow-out preventers installed below the snubbing rig employ large-bore hydraulic cylinders to block off the well pressure below after a joint has passed. Blow-out preventers must work quickly and with intent and operate with the aid of many large accumulators.
The hydraulic power and control systems for both snubbing rigs and BOP’s must also avoid contributing to dangerous operation. Fire-resistant hydraulic fluids, such as water-based options, prevent contributing to the already dangerous potential for fire. Also, all hydraulic power unit solenoid valves and electrical components must be designated “explosion-proof,” meaning they must not create electrical sparks or arcing during regular operation. Any crude oil blow-out in the presence of a spark makes for very dangerous and difficult to extinguish flames.
In writing this article and knowing how prolific oil & gas wells are across our continent, I researched the presence of oil and gas wells in the Finger Lakes Region of upstate New York, where Ithaca sits at the bottom of Cayuga Lake. Although some previously active wells nearby have since been closed, there exists a veritable mosaic of gas wells scattered on the map on either side of Northern Cayuga Lake. It seems the two worlds of hydraulics are more closely situated than I previously thought.
Filed Under: Cylinders & Actuators, Technologies, Trending, Valves & Manifolds