Drilling Minute – Directional ROP

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In drilling, time is money, so we usually want to drill the well as fast as we safely can. This drilling minute explains how drilling speed, or ROP, is measured.

How is ROP Measured?

ROP stands for “Rate of Penetration,” which is basically how fast the bit is drilling the hole. Average ROP is generally measured by taking the total distance drilled divided by the time it took to drill it. For example, if you drill 1000 feet in 10 hours, 1000’ divided by 10 hours is 100 feet per hour – on average.

But average ROP doesn’t tell the whole story. Let’s say, for example, you leave your house and it takes you one hour to drive to a rig about 40 miles away. We could say that you drove at 40mph. But what if you drove 70 miles per hour most of the way, and 10 miles per hour the rest? 40 miles per hour would be your average speed, but your instantaneous speed was 70mph and 10mph at different parts of the trip. In drilling, instantaneous ROP usually refers to the maximum, real ROP through an interval or formation.

Rotating vs. Sliding ROP

Just like in driving, you can go faster in a straight line than you can around a curve. While drilling straight ahead in rotating mode, the drill string rotation reduces the drag on the drill string, allowing weight to transfer more directly to the bit. While steering, the static contact between the drill string and the well-bore causes a lot of friction, or drag. Because of the drag, there is less weight available to drive the bit ahead, which is why sliding ROP is usually much lower than rotating ROP.

Understanding Limitations

Because ROP is used to try to understand the limits of the bit and drilling operations, it is important to record it accurately and specifically. Average, instantaneous, sliding, and rotating ROPs are all important. In many cases, recording the sliding and rotating footage and hours is the best way to document the ROPs. This information and much more can be found on the directional driller’s slide sheets and BHA report.

There are many other components that affect directional performance, like motor configuration, which will be the topic of the next segment.

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