Improving Reliability in “The Tough Section”

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Interbedded. Ratty. Transitional. Regardless of what you call it, it is one of the biggest challenges to drilling performance that the industry has been dealing with in the last few years. When rock is formed, at least most of the rock that we drill through, it does so in distinct layers that have different structures and properties.

Due to the transitions between layers of harder and softer rock types, the drill bit may experience difficulties with differing force concentrations across the cutting structure, leading to potential cutter overload and premature bit failure.

In the most challenging applications, these transitions are stacked close on top of each other so that the bit faces a difficult gauntlet which often leads to failure.

Historically, the answer to this challenge was to build in excess durability to the bit design so that it could survive this transitional part of the section and go on to drill to the target depth (TD). This approach could be partially successful in that aim, but bit design is always a compromise between durability and speed, so these bits drill slowly and with reduced efficiency. The bit engineer would have to tread a very thin line between delivering increased performance without compromising too much durability to be able to survive through the transitional zone.
The 12 ¼” intermediate section in the Permian Basin is one such application and it is probably the most important transitional drilling application in the world with approximately half of the US rig count drilling in this region. This vertical section starts shallow at around 500 to 1,000 ft with relatively easy drilling and section TD is about 7,000 to 8,000 ft later. In between these two points and deep into the section are the Cherry and Brushy Canyon formations, a series of highly interbedded limestones, siltstones, and sandstones that have a reputation for damaging PDC drill bits. These formations are the key to success or failure in this section. If the bit makes it through, then it is highly likely it will drill all the way to the end of the section. But, if not, then the operator must pull the drill string. Only 60% of bits make it through, with the other 40% causing hundreds of thousands of dollars of additional time and resources on each well.

The Problem

Recently, a major US operator, in conjunction with other industry leaders, invited Ulterra to directly address this problem and come up with a new bit design that would improve performance in the Permian Basin’s 12 ¼” section. None of the involved parties knew what the eventual solution would look like, but all expressed a desire to improve durability and reliability with the recognition that small increases in performance in this application alone could save millions of dollars over longer periods of time, not to mention all similar transitional drilling applications worldwide.
At Ulterra, the innovation philosophy leads with the question, “What problem are you trying to solve?” whereby every challenge is broken down into its component parts so that each component can be properly addressed. In doing so, you can make sure that the root cause of the issue is being addressed as opposed to the symptoms. In initial meetings, the problem of interfacial severity was correctly identified, and the application was characterized so that everyone had a full understanding of the problem. When you break down interfacial severity further, a major issue is that different parts of the bit profile are subjected to uneven loads from hard and soft lithologies at the same time.

The Solution

Ulterra’s Engineering Team was then tasked with finding a solution once the problem was correctly defined as “How do we deal with unpredictable axial forces without limiting performance?” Traditional depth of cut control uses surfaces or secondary components built into the bit as a barrier to prevent the cutters from penetrating deep into the formation. While highly effective at restricting depth of cut, these barriers only engage at a pre-defined penetration rate. In an application where penetration rate varies so significantly through hard and soft layers that solution can only work by limiting performance. The epiphany came in realizing that erratic axial cutting forces don’t have to be simply limited, they can be better distributed.

The Engineering Team’s solution built on the proven technique used by CounterForce® technology to deal with lateral drilling vibrations, using the existing cutting structure to control depth of cut without putting in penetration rate limiters. Given the name

RipSaw™, the technology uses alternating back rakes which work side-by-side to better distribute the drilling forces across the entire cutting structure. The high back rake cutters are more resistant to depth of cut changes, taking on the higher forces for which their orientation is suited to handle, whereas the low back rake cutters along side continue to aggressively cut the formation. The greater the force trying to push those high back rake cutters in to the formation, the more they resist that change meaning they effectively work like shock absorbers to smooth out fluctuation. Unlike other depth of cut solutions, these components are still primary, active PDC cutters – engaged at any depth of cut – so there is no ceiling on penetration rate.

Managing depth of cut in this way helps to control the forces across the bit profile as it drills through different layers of a transitional application, preventing cutter damage and increasing durability. By keeping depth of cut more consistent, reactive torque produced by the bit is smoothed and controlled. This creates many advantages across a whole variety of non-transitional drilling applications, such as better tool control, lower vibration, and management of weight control in high torque and drag wells.

The Proof

This new technology was incorporated into one of Ulterra’s most successful designs for the 12 ¼” Intermediate Section for testing in West Texas and immediately started producing good results. Reports from test runs showed increased durability and reliability to drill through the Cherry and Brushy Canyon formations. The test bits that were equipped with this technology showcased the results in quantifiably improved dull conditions.
While great individual performances are good to achieve, one-offs can happen for anyone. True, sustained improvements in reliability are very difficult to prove and require exhaustive testing. RipSaw technology was tested across nearly 2,500 runs and over 8 million ft drilled in transitional applications in the Permian Basin alone. Statistical analysis of this huge data set shows that RipSaw bits more reliably make it to any target depth by a huge margin over competitive offerings and come out of hole with a dull condition that is also nearly 30% better based on IADC gradings. Despite having engineered passive elements, keeping the bits in sharp, drilling condition has also yielded several speed records as well.
These reliability gains are incredibly significant in the Permian where the drilling industry has pursued a policy of ruthless efficiency gains over the last few years. Extrapolating the average cost per foot saving of running this new technology in the 8,000,000 ft of test drilling, the cost savings to Permian operators has been in the hundreds of millions of dollars.

Better Together

By applying the “What problem are you trying to solve?” philosophy, Ulterra has successfully created a portfolio of technologies that are each designed to address a particular problem or dysfunction. These technologies are not exclusive or confined to specific product lines, rather they are complimentary and can be incorporated synergistically into new designs whenever they are needed. RipSaw Active Torque Technology is now being recognized as another of these industry-leading technologies thanks to the problem-solving approach at Ulterra.

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