Extreme Drill Rate Performance

This link is to a presentation by Fred Dupriest on extreme performance in drilling.

Yes, Decreasing WOB Increased ROP!

Being employed as an MWD hand frequently leads to interesting and frustrating interaction on the rig. Often times the MWD hand is not viewed in a good light, particularly if they are new (unproven) on that particular rig and/or their qualifications aren’t known. One thing that I’ve found to be most interesting is the widespread misconception that increased WOB always results in increased ROP. In one instance I’ve even witnessed temporary WOB reduction test increase ROP only for WOB to brought back up, resulting in decreased ROP, because “higher WOB increases ROP”. So, we’re going to take a look at that today to clear things up.


The relationship between ROP and WOB is determined by either a step rate test or drill-off test. Both tests, despite different procedures, yield ROP vs WOB information that can be plotted and used for optimization efforts. The plotted test results will typically yield a curve as shown in Figure 1.





On inspection of Figure 1 it becomes immediately apparent that increasing WOB does not always increase ROP. At low WOB it is apparent that the relationship between ROP and WOB is nonlinear. As WOB increases the results indicate a linear relationship. At some WOB the curve deviates from linear behavior. After some maximum ROP the rate of change of ROP with respect to WOB becomes negative and the curve begins to slope downward. The range over which a straight line can be plotted is often said to be where ROP is proportional to WOB. Although most would understand what is meant by saying ROP is proportional to WOB, it should be noted that it is not truly proportional. For the relationship to be proportional the straight line must pass through the origin.


The straight-line region of the plot is where the bit is working with greatest efficiency. The highest WOB at which a straight-line relationship is exhibited is known as the founder point, as shown in Figure 2. Above the founder point some sort of inefficiency, such as vibration, bit balling, or inadequate hole cleaning, starts to influence the ROP. At any WOB after maximum ROP is achieved the inefficiency becomes so severe that it is removing such a large amount of energy the ROP begins to decrease.





If the inefficiency can be rectified it may be possible to increase the WOB at which founder occurs. For example, if the inefficiency is inadequate hole cleaning it may be possible to increase flowrate thus increasing the point at which founder occurs. The changes to the curve made by identifying and removing the inefficiency can be seen in Figure 3. Keep in mind that removing the inefficiency will not shift the curve or increase the slope of the straight-line region. Rather, it will extend the straight-line region, increase WOB at founder, and increase maximum ROP. Additional considerations must be made when attempting to address inefficiency to prevent unsafe drilling and premature equipment failure.





To conclude, we have seen that increasing WOB does not always increase ROP due to inefficiency. The inefficiency may be caused by a number of issues but the most common are inadequate hole cleaning, bit balling, and vibration. There exists some maximum ROP that occurs outside of the efficient range of drilling. While it is possible to drill at the maximum ROP it also increases the likelihood of premature wear or damage. Premature wear may decrease the founder put to the extent that the initial ROP advantage is completely erased or an early trip is required.


Understanding the mechanics of drilling is essential to completing the project in a timely and cost-effective manner. Real time monitoring systems and EDR’s can tell detailed stories. Don’t be afraid to put some trust in the people on your rig tasked with monitoring them!