Sure, you’ve seen and held a frac plug, maybe you’ve even watched some of the many YouTube animations about how they work. Still, it’s hard to wrap the mind around how these frac plugs are functioning down hole. Making an informed decision on which plug to use means understanding its complete performance of operations during the entire process of setting, frac, and mill up. Let’s discuss what we can fairly expect from a traditional frac plug, what issues may arise, and how our composite frac plug measures up.
Use of Frac Plugs
Frac plugs are employed to isolate zones in a well for hydraulic fracturing. The well is drilled, and metal casing is installed. Yet, before production can start, the well must first be hydraulically fractured. To accomplish this, a perforating gun is sent down the well to blast holes in the casing. Fluid pumped into the well surges out of the holes and into the rock, breaking it apart. In a finished well, oil flows from these cracks into the well and up to the surface.
After hydraulic fracturing of one section, a frac plug is inserted just above it. The plug isolates the already fractured zone from the rest of the well enabling the next section to be fractured without loss of pressure from pumping fluids through the previous sections perforated casing and fractured rock. This process is repeated multiple times in a single well, meaning multiple zones are all fractured, and isolated by frac plugs.
How A Composite Frac Plug Works
Seven Canyons Composites frac plug build up includes a mandrel, upper slip, sleeve, and cone; seal element; and a lower slip, sleeve, and cone. The core of the plug is the mandrel. Other components ride on the mandrel. On our SCC frac plug the upper sleeve or build-up is an integral part of the mandrel and contains holes on the O.D. for the setting tool to be anchored to for setting the plug. The lower sleeve is bonded on and pinned to the mandrel. Both sleeves constrain the previously mentioned components on the mandrel. The slips and cones interact with each other in a way that allows the slips to move outward and touch the casing. Hardened edges on the slips bite into the casing, locking them in place during the setting process. Seven Canyons composite frac plug has been tested to withstand pressures of 10,000 PSI for at least 1 hour, with a max pressure of 11,000 psi max operating temperature of 300 F. Hydraulic fracturing a section of the well takes approximately 20 minutes. Our plug will hold lower pressures much, much longer.
We engineer the slips on the frac plug to stay together until the setting sequence breaks them apart, at which time the slips move up on the cone and bite the casing. Our plug works with the Baker Hughes 10 E-4 WLPSA (Wireline Pressure Setting Assembly) setting tool. Once set, the lower slip holds the full force of pressure while the upper slip keeps the plug compressed. The sealing element creates a tight seal between the inner diameter casing wall and the mandrel. This seal isolates the area to be perforated and fractured. An FWC 2.25 Frac Ball is dropped down the well to settle in the ballseat area of the frac plug and complete the sealing of the mandrel. The frac ball does not need a wire connected to put in place. It’s simply dropped into the well and travels down to the frac plug with the pumped fluid at the same time of lowering the perforating gun to frac the next stage. Now, the zone is ready for hydraulic fracturing.
This process is repeated. A new frac plug is lowered by wireline down the well and set in a new location up from the last plug, sealing off a new area for hydraulic fracturing. Once the entire well is finished, usually done in 1-2 days, the frac plugs are drilled out. Our composite plugs have a faster milling time than metal plugs thereby increasing production and saving time and money. In addition, Seven Canyons Composites FWC 2.25 Frac Ball is manufactured via a patent pending filament winding/compression molding process to withstand sheering, eliminating delamination issues seen with other composite frac balls
During the pump down sequence, the frac plug, setting tool, and perforating gun can be lowered into the well using coiled tubing, or wireline (cable). Once at the correct position, the setting tool is actuated, and the plug is set. The tool is then removed. At the point of positioning, the main function of the plug is to stay together as it’s dropped down and pumped to its intended location. A malfunction of the slips here would cause the frac plug to become lodged in the casing causing a potentially costly preset event. Our frac plug is built to withstand normal pump down speeds and pressures until activated during its setting sequence providing a smooth transition for each zone.
Additionally, the sealing element needs to stay in place, or you’ll encounter similar problems. There’s typically a small gap, approximately 0.2” in circumference, that allows bypass during down pumping with all frac plugs. This bypass causes a low-pressure zone to form around the plug due to speed at which the frac plug is moving and the flow rate of fluid. The results of this low-pressure zone could be the expansion of the element to contact the casing. To prevent this situation, following provider protocols for flow rates and plug speeds is paramount. Failure to do so may result in malfunction.
When drilling the frac plug out at the end of the hydraulic fracturing cycle, it’s important how the plug performs. As mentioned previously, a composite frac plug drills out faster than metal plugs, however, even among composite plugs there can be a difference in how the mill out proceeds. How the components react to the milling process is important. We design the lower slip to hold the plug in place against forces up to 11,000 psi multiplied by the area of the casing inner diameter. This holds true for milling as well. The bit weight is much less than what the plug can hold and therefore the lower slip holds the plug firmly in place as its drilled. Once the milling proceeds past the lower slip, the remaining components wash down to the next plug and settle against the mandrel and frac ball. It’s of utmost importance that the remaining pieces get locked into the next plug, otherwise they will spin and prevent the bit from establishing a hold on the next frac plug. Our frac ball design acts as a bearing to lock the pieces in place as they’re milled out with the next plug on down to the very last one. This prevents costly delays that would otherwise occur during milling. If the pieces were to continue to spin, all downhole equipment would need to be removed from the well in order for the pieces to be flushed out so the next zone could be milled. Situations like this frustrate the process and add unnecessary time and spending to drilling. The FWC series frac ball accomplishes its job to lock down leftover pieces of the plug for milling.
Seven Canyons Composites
The use of expertly designed and manufactured composite frac plugs can increase well production and reduce cost and time. Seven Canyons Composites exceeds the industry standard and ensures components that are fashioned to optimize the hydraulic fracturing process from setting to milling. Contact us for information on bulk pricing.