Modern shale gas exploration means more horizontal wells, longer laterals and more frac stages. The market shift to horizontal wells has also brought different horizontal frac completions methods. The benefits and drawbacks of two of them, “plug and perf” (or limited entry) and pinpoint fracturing, continue to spark debate among operators.
We won’t solve that debate here. The technical discussion is far from over. But we can briefly look at the two completion methods and outline their characteristics. What’s the difference between limited entry and pinpoint entry, and what are the pros and cons of each?
Limited Entry Fracturing
Plug and perf (or limited entry) is the preferred and most common fracturing method for unconventional wells. Often employed in wells with cemented liners, it involves pumping down a bridge plug on wireline with perforating guns.
The operator sets the plug at a horizontal location near the well toe, and the zone is then perforated. Next, the tools are removed from the well, and the fracture stimulation treatment gets pumped in. A ball-activated plug diverts fracture fluids through the perforations and into the formation. As the operator repeats the “plug and perf” process for each stage, the downhole tools move from the end of the wellbore back to the beginning until each stage has been fraced.
Limited entry operations are predictable and repeatable—two things operators love. However, limited entry comes with its limitations.
One disadvantage is that it creates multiple permanent entry points per target fracturing stage, with multiple perforations per entry point over dozens of target stages along the length of the wellbore.
Since multiple perforation clusters are stimulated simultaneously, there is no control over the size of each fracture. Some clusters are not stimulated at all, while others receive varying amounts of treatment. The result is gaping areas of the formation that remain unstimulated.
This lack of control during frac placement opens the door for disruptive technologies that address these concerns in very tangible ways.
Which leads us to “pinpoint” fracing …
Pinpoint Entry Fracturing
With limited entry (discussed above), drillers frac multiple clusters ( a group of perforations intervals or zones) at the same time. Most drilling operations in the United States include five clusters per stage. Some oil and gas operators are experimenting with an increased number of clusters (up to 16 per stage).
There’s a significant group of big operators (including ExxonMobil, Shell, Apache, among others) that seem to be convinced it is extremely challenging to accurately and equally frac each zone, all at the same time, with limited entry. Therefore, they prefer to treat each area individually. That’s where pinpoint, or single-point entry, fracturing comes in.
Pinpoint fracturing can improve near-term and long-term well performance compared to plug-and-perf. It provides consistent, repeatable fracture placement along the entire lateral of each well and from well to well.
Zones are isolated with sand plugs, and operators can frac each cluster individually with coiled tubing in the well. This approach allows operators to optimize the stimulation design for a given formation.
Locations of fracture initiation are verifiable and consistent because pinpoint fracturing treats a single cluster at a time. The amount of proppant and fluid pumped into each fracture is consistent.
Pinpoint fracing has been growing in popularity, and many service companies have designed completions systems around it. Indeed, several completions companies are cropping up lately that sell specialized tools for unconventional multistage fracturing. That said, one of the big selling points of pinpoint stimulation is that it requires less equipment and a smaller footprint.
Operators who end up going back to plug and perf say the maximum number of stages they can frac with pinpoint stimulation is a limitation, as is the pump rate they can achieve. They also cite cost and operational inefficiencies.
For example, one of the most successful pinpoint frac systems these days comes from NCS Multistage. The systems are limited by the maximum depth and flow rate they can achieve; both issues are because they require coiled tubing to activate their sleeves.
What Do You Think?
While many single-point entry fracturing adopters have found it increases oil production, several big players stick with the more traditional plug-and-perf method. What’s your opinion? What do you think is next in stimulation technology? What emergent methods will be the next “big thing” in hydraulic fracturing?
Get in touch with us and let us know what you think. If you need support and stability from a manufacturer with over fifty years of experience in designing, manufacturing and delivering high-quality oilfield tools, Keystone Energy Tools will be happy to assist you.