Tag Archives : CounterForce

Weight On Bit – WOB

What is Weight on Bit or WOB?

An essential part of the drilling process is adding force to the drill bit in order to successfully break the rock. Weight on the Bit, or WOB, is the amount of downward force exerted on the drill bit provided by thick-walled tubular pieces in the drilling assembly that are known as drill collars. The downward force of gravity on these steel tubes provide force for the drill bit in order to effectively break the rock. The weight of the drilling assembly is controlled and measured while the drill bit is just off the bottom of the wellbore. Then, the drill string is slowly and carefully lowered until it reaches the bottom. As the driller continues to lower the top of the drill string, more of the weight of the assembly is being applied to the bit and harmoniously less weight is hanging at the surface.

To put this into perspective, let us imagine a vertical drilling hole. If the surface measurement reads 1,000 kg less weight of the string while drilling than with the bit off the bottom, then there should be 1,000 kg of force transferred to the bit. This measurement is read using a hydraulic gauge at the surface that is directly connected to the hoisting equipment for maximum accuracy. This measured weight includes everything that exerts tension on the drill string. Weight transfer control can greatly decrease operating cost and time, and lead to a longer lasting drill bit.

Weight on bit is an essential part of drilling optimization to ensure that the well deepens as drilling moves forward. Finding the right amount of WOB per application is crucial to drilling operations. If the WOB is greater than the optimum value, the drill bit has a higher chance of wear or damage and there is even a chance for the drill string to buckle. On the contrary, if the WOB is less than optimal, the Rate of Penetration (ROP) slows down and drilling performance is subpar. The ROP is the speed at which a drill bit breaks the rock or sediment; ROP is typically measured either in feet or meters per hour. It is important to maximize the rate of penetration to reduce rig time and cost. In order to optimize penetration, drilling operators must pay close attention to Weight on bit and alter it as necessary. Finding the optimum WOB is determined by the design and parameters of the drill bit, as well as external factors such as mud weight, BHA, and the rock being drilled. There is no standard range of weight that should be applied to the bit. It can be anywhere between 1,000 lbs. to 100,000 lbs. depending on the size and type of bit, the rock being drilled, and the application. At Ulterra, recommended values for WOB to the customer are based purely on local knowledge and experience of the application.

Bit manufacturers specify the maximum WOB to avoid damage to the bit; each will have their own method that helps them determine this maximum weight. The stable zone for smooth drilling operations calls for moderate WOB and rotary speed. The recommended weight provided by bit manufacturers is determined by factors such as the structural integrity of the bit body and blades, cutter quantity and the cutter orientation, size, and shape. When we determine the maximum weight the design will take before failure, we then add in a 10-20% safety factor. This safety factor provides a guarantee that the bit will not break if the maximum specified Weight on bit is applied during drill operations.

WOB Measurement

Weight on bit is usually measured using a drillstring weight indicator located on the driller’s console and linked to the hoist equipment in the derrick. The more advanced and functional indicators have dual scales which consists of a primary scale indicating the suspended weight of the drilling assembly and the secondary scale for the drill bit weight. These weight indicators are hydraulic gauges that are attached to the dead line of the drilling line that take the actual force measurement. As the tension in the line increases, hydraulic fluid is forced through the instrument which turns the hands of the indicator, providing the operator with the weight suspended off the hoist. Before the driller measures the weight on the bit, they must make a zero offset adjustment to account for any weight other than the drillstring. Therefore, the measurement inclusively measures the weight of the drill string, which includes the drill pipe and bottomhole assembly. Other than these indicators on the surface, Measurement While Drilling (MWD) tools that are located down hole provide more accurate weight on bit measurements that are sent to the surface on a readout interface. Sensors inside the MWD tool measure the strain on the body of the tool, from which they can calculate the applied weight that is actually getting to the bit since the MWD tool typically sits very close in the drilling assembly.


Finding Optimum WOB & Rotary Speed

It is important to select the best bit weight and rotary speed to optimize the drilling operation, minimize cost, and increase bit life. The drilling environment, such as the lithology of the rock and drilling dysfunction, impacts the drilling conditions and can have a negative effect on drilling efficiency. Rotary speed and weight on bit can control vibration and ROP. It is important to be in control of drilling vibration in order to keep the bit in smooth contact with the rock, prevent damage and maximize efficiency by reducing wasted energy. A minimum WOB must be achieved in order to get the drilling started, which is considered the threshold weight. There are average values that have been determined for drilling weights, but proper weight can be determined for each application by increasing the bit weight in steps of 1,000-2,000 lbs., with an optimized rotary speed. Optimum weight has been reached when additional weight is not providing further penetration and the bit starts to founder.

Rotary speed and weight on bit cannot be continuously increased without causing extreme stress on the drill string and bit. If excessive force and weight are being applied to the drill string it can cause the drill pipe to buckle. Buckling at a minimum leads to decreased performance and increased stress on components, but it can even result in parting the string and losing your BHA, which means losing expensive high-tech logging equipment and directional drilling tools down the hole.

After a certain bit weight value is reached, it is normally observed that rate of penetration starts to reduce. The poor response of penetration is usually attributed to inefficient bottom hole cleaning and wear on the drill bit, but it is often actually the case that drilling dysfunction starts to kick in. At very high WOB the sheer amount of torque being produced by the bit starts to overload the drilling system leading to vibration and inefficiency. Likewise, after a certain value of rotary speed has been met, ROP decelerates as the bit starts skating on top of the rock rather than getting good penetration of the cutting structure, the speed is too high to get a good bite into the rock. This poor response of decreased penetration is likely due to loss of stability of the drilling assembly in the wellbore.

To test bit performance, the driller can increase WOB by x amount and the drill rate will increase by y amount of ft/hr. If this bit is efficiently shearing the rock, the next x amount of weight on the bit should yield another y amount of ft/hr. If the drill rate does not increase by the same amount, the response is disproportionate. That increased weight could be damaging to the bit or the BHA. These tests of efficiency will help determine how proportionate the response is between WOB and ROP (ft/hr).

Rotary speed and weight are just two parameters that must be monitored and adjusted to improve drilling efficiency. Other drilling parameters such as torque, flow rate, bottom-hole temperature, and bottom-hole pressure can also be converted into ROP at the bit.


Lower WOB, Higher ROP

Ulterra assembled a team of material specialists, design engineers, and performance optimization experts to create a PDC bit platform that was superior to both traditional matrix and steel PDC bodies and that would allow the cutters to get deep into the formation to increase ROP. This team of experts ended up creating the FastBack™ series of bits, which are designed to drill faster with lower WOB. FastBack is designed to get the bit body out of the way so that the drilling is focused on the sharp, diamond edge of the PDC cutter. The energy provided by the PDC cutting structure in these designs requires less WOB while still providing a greater ROP than traditional bits.

Ulterra also offers CounterForce® technology which is focused on the cutter orientation to maximize rock failure and drilling efficiency. CounterForce cutters work synergistically to engage the formation and optimize crack propagation by re-directing resultant drilling forces back into the rock. The angles of the cutters are designed to shear rock more efficiently while keeping the cuttings moving away from the crucial sharp edge of the cutter. This helps reduce reactive torque and improves bit stability for better control and wellbore quality.

With both of these advanced technologies from Ulterra, less weight on bit is required to drill because the bits are more efficient at translating the energy from WOB into cutting action. This translates into a wider envelope of useable drilling parameters, less possibility for drilling dysfunction and overall reduced rates of damage to the bit.







Hart’s E&P June 2017

Featured in the June issue of Hart’s E&P, Ulterra discusses how new bit designs are pushing drilling boundaries. Over the past year, Ulterra has looked critically at bit design, blade geometry, cutter reinforcement and hydraulics and has been testing new materials, which has resulted in its XP™ line of polycrystalline diamond compact (PDC) bits. With the increased energy going through the bit, it is Ulterra’s goal to make sure the bits do not become the limiting factor in performance.

Hart’s E&P June 2017

Read the full article from Hart’s E&P here.

Ulterra Celebrates Recent Success with Operator in the Northeast US

By: Kerry Sisson, District Manager

Operators in the Northeast US have been drilling wells with increasingly complex well plans. Due to this, they have been looking more to rotary steerable systems (RSS) to reduce slide time in the lateral and increase directional flexibility and responsiveness. As a result of the down market, RSS have become a more affordable and viable option and Southwestern Energy is certainly not an outlier in this trend with their operations in West Virginia and Pennsylvania.

Ulterra was granted an opportunity to participate in the curve and lateral on Weatherford’s motorized point-the-bit RSS, drilling a Marcellus well with Southwestern Energy. To be competitive in this interval, a bit design must be both toolface friendly to complete the curve and aggressive enough to rotate in the lateral at a high rate of penetration (ROP). Ulterra’s solution was the 8.5” U516M, featuring patent pending CounterForce® technology. CounterForce uses its unique cutting structure to reduce vibrations at the bit, which increases efficiency and reduces bit damage. Reducing vibration is important on wells which utilize RSS since most RSS tools are highly susceptible to failure due to vibration.

In the first two runs Ulterra had with Southwestern in 2016, the 8.5” U516M CounterForce had the operator’s two fastest curve-lateral runs in the state of West Virginia. The runs were an average of 38% higher ROP than the competitor average on the previous pad.

World Oil October 2016

Featured in the October issue of World Oil magazine, Ulterra discusses PDC bits for RSS applications.

To extract the full potential of different RSS types, operators have sought out drill bit manufacturers, to provide designs tailored to specific parameters and BHAs. Ulterra has utilized its proprietary technology to develop CounterForce™ PDC bits, designed specifically to reduce lateral vibrations, a leading cause of downhole tool failure.

PDF_download_Icon World Oil October 2016

Ulterra Continues to Expand the Application for CounterForce®

By: Matt Case, Lead Engineer, Eastern U.S.

Ulterra Drilling Technologies continues to expand the application for its ground breaking CounterForce® cutting structure technology.  CounterForce uses the cutting structure to reduce vibrations at the bit, which increases efficiency and reduces bit damage.  Reducing vibration is particularly important on wells which utilize Rotary Steerable Systems (RSS), which are becoming more popular as well planners are pushing the limits on directional difficulty and lateral lengths.  Most RSS tools are highly susceptible to failure due to vibration, which is one of the most common reasons the BHA must be tripped.  RSS directional hands will often monitor these vibrations and are forced to reduce drilling parameters, and sometimes stop drilling altogether to pick up off bottom when vibrations get too high.  Vibrations in a way act as an ROP ceiling, limiting the driller to lower parameters than what is necessary for maximum ROP.  With the ability of the CounterForce cutting structure to reduce vibrations, we can not only reduce the number of trips for tool failures, we can also effectively elevate the ROP ceiling so that operators can drill faster and still avoid high vibrations.

The claim that CounterForce can reduce vibrations, and therefore increase ROP and reduce the number of trips is validated through numerous field runs verses competitor bits.  A major operator in South Texas utilizes the Weatherford Revolution Rotary Steerable System to drill out from under surface through the curve and lateral to TD in one trip.  Comparing the Ulterra CounterForce U516M verses competitor bits in this application in the year 2015, the U516M on average drilled 10% faster and was tripped 32% fewer times for tool failures.  With 41 runs within this time frame, the U516M is the performance and market share leader for this operator.

CounterForce performance has also been validated through electronic drilling recorder (EDR) analysis.  A four well pad in South Texas utilizing the Waterford Revolution RSS ran the CounterForce U516M on three wells, and a competitor bit on the fourth.  The stick-slip magnitude, measured in a rotational value of c/min, was 35% lower for the average of the three CounterForce runs compared to the offset.  In addition, the average ROP for the three CounterForce runs was 27% faster than the offset, saving the operator 13 hours on each well the CounterForce U516M was in the hole.

CounterForce technology has also been tested in demanding applications offshore in the Gulf of Mexico.  A major operator drilling in the Eastern GOM utilized the Ulterra 16.50” U713M CounterForce to drill a 2,600 ft. section through the Base Miocene and Cretaceous formations.  This operator was particularly concerned with high vibrations through these formations due to offsets they had drilled in the past.  The Ulterra U713M CounterForce was able to decrease stick-slip vibration by 30% and increase ROP by 14% compared to said offsets.

Oilfield Technology June 2016

Featured in the June issue of Oilfield Technology, Ulterra discusses how customized bit development for RSS reduces tool failure.

Most RSS tools are highly susceptible to failure due to vibration, which is one of the most common reasons the BHA must be tripped. Ulterra’s CounterForce® technology uses the cutting structure to reduce vibrations at the bit, which increases efficiency and reduces bit damage.

PDF_download_IconOilfield Technology June 2016

Hart’s E&P June 2016

This article was sourced for a recent article in Hart’s E&P magazine, which can be found here.

Working, Together: RSS-Tailored Bit Designs Improve Drilling Performance

Written by: Aron Deen, Levi Sasser, and Chris Gooch

Nearly all new technologies struggle in their infancy to gain adoption due to high cost, problematic reliability, lack of understanding, and marginal value proposition.  Over years of learning, development and refinement these hurdles reduce, and with each step new opportunities open up.  This has been the case for rotary steerable systems (RSS), which is finding new value in this historic downturn.

Another facet of technology adoption is the availability of compliments.  For example, smartphones need great apps for customers to realize their true value.  In much the same way, RSS need to have great drill bits designed to work with them in order for operators to realize their maximum value.

To be sure, there are certainly some hurdles in working across company lines on product development.  For example, gauge pad configuration is one of the many aspects of bit designs that are customized to work perfectly with differing RSS tools.  Different lengths, steps, tapers, helix angles, and wear protection may be advantageous for a particular RSS application, but producing such a specific product requires a significant investment of engineering resources and capital.  And once created, such a bespoke asset should not be blindly forced into an improper application to the detriment of another operator.  The only long-term path over such hurdles is for service companies to jointly commit to focus first on performance for the customer.

World Record RSS runs in Eagle Ford

In South Texas, operators and RSS tool developers have toiled for the last few years to uncover the full value proposition of being able to steer while rotating.  In theory, this should allow operators to capture all of the benefits of highly directional wells without the inefficiency of regularly having to interrupt operations to orient and slide at low ROP – and have better hole quality to go along with it.  The increased complexity of the systems, however, requires all components to work together seamlessly.  The primary challenge for operators has been maintaining ultra-tight windows in lateral applications of the extended-reach horizontals in the Eagle Ford.  RSS has made those complex well designs a possibility.

Ulterra’s willingness to partner with RSS makers has contributed to great runs.  After working with Weatherford to design an Eagle Ford bit tailored to Weatherford’s Revolution® RSS, there has been a huge improvement in vibration and torque, which has drastically reduced the chance of tool failure. At the same time, the bit is increasing ROP, setting distance records, and coming out of the hole in pristine condition.

In a run in Live Oak County, TX, the bit set three global footage records for the Revolution RSS by drilling 16,234 feet in one run.  The extended-reach well had a total depth of 22,700 feet.  Reaching out that far is a big challenge, and accomplishing it with one bottom-hole assembly had been previously unheard of.  With the Ulterra bit and Weatherford RSS working together the BHA was able to stay on bottom for 192 hours.

Reduced Vibration, Improved Efficiency in Abu Dhabi

In a recent well in Abu Dhabi, a major operator encountered difficulty drilling through a troublesome series of formations in an ADMA brownfield while utilizing the AutoTrak X-treme™ motorized RSS from Baker Hughes.  Based on data from their CoPilot™ system, vibration was identified to be one of the major performance limiting factors in two bits that had failed to complete the section.  As this was the case, the operator turned to Ulterra to provide a custom solution.

One of the unique design technologies that Ulterra has to combat lateral vibration at the bit is CounterForce®, a novel cutter arrangement methodology that allows the cutters to work together to redirect vibrational energy back into the rock.  By pairing this technology into a U713M bit design along with the RSS, the operator was able to complete the interval.

The Ulterra bit delivered, allowing the RSS assembly to drill 824 feet to section TD at an ROP of 23 ft/hr. This run was 66% faster than the average of the two previous bit runs in mother hole and 230% faster than the average of the two previous bit runs in pilot hole. According to the operator, this performance saved three trips. The dull condition was also excellent with only minimal abrasive wear to some of the cutters on the nose and shoulder.


More importantly to the operator, the MSE calculations from the CoPilot down hole measurement tool showed that the Ulterra bit, with CounterForce technology, achieved this using 14% less energy to drill compared to the previous runs that had mostly drilled in softer, easier formations. Vibration levels were also dramatically reduced in the most difficult formation where it causes the most issues.  Compared to other bit runs, lateral vibrations and whirl were reduced by 84% and 31% respectively, while stick-slip was reduced by 88%.

Best for Best

Some RSS makers, such as Weatherford, Gyrodata, Scout Downhole, and others, focus their energy and expertise on their tools and services while leaving complimentary performance parts to other experts.  Others produce their own OEM (original equipment manufacturer) drill bits, and obviously they will often recommend them with self-benefiting reasons.  However, in high-cost, high-performance applications, which are often identifiable by the use of RSS, “stock” equipment is seldom the best option.

As a PDC drill bit company, Ulterra is always excited for the opportunity to tackle new and unique problems.  Our mission is to be the most trusted employer and supplier of PDC drill bits in the industry, and to reward that trust with industry leading consistency, performance and relentless, rapid improvement.  There are many great car makers, but they all rely on other companies for the best tires in the world.  While Ulterra doesn’t make RSS tools, the evidence is growing that we do make the best bits for them.

Ulterra CounterForce™ and TorkBuster® a Winning Combination for Major Operator in Central Australia

A major operator in central Australia recently achieved significant time and cost savings thanks to the combination of the Ulterra TorkBuster matched with the U513M CounterForce drill bit. The combination of TorkBuster and CounterForce proved to be a rock destruction solution within the challenging Permian, with the operator increasing ROP by 52% and achieving total savings of $150,000.

Download PDFCounterForce and TorkBuster a Winning Combination