Interpreting High ROP in the Context of Drilling Efficiency

A high instantaneous drilling rate can coexist with dysfunction, inefficient energy transfer, bit degradation, or poor wellbore quality. ROP is an outcome; understanding the quality of that performance requires context.

Rate of penetration is one of the most intuitive measurements in drilling.

If one interval is drilling at 220 ft/hr and another at 160 ft/hr, it is natural to call the first interval better.

Sometimes it is.

But ROP answers a relatively narrow question:

How quickly are we making new hole?

It does not directly tell us how efficiently energy is being transferred to the rock, whether the drillstring is experiencing damaging dynamics, whether the bit is deteriorating, whether the wellbore being left behind is smooth, or whether the operating point can be sustained.

That distinction becomes important when drilling performance is evaluated in real time.

A high ROP can occur while the system is experiencing stick-slip. It can occur shortly before bit performance deteriorates. It can occur under conditions that challenge hole cleaning. And a fast lateral can still leave a wellbore that is more difficult to trip, case, complete, or subsequently operate.

In other words:

ROP is a performance outcome, but it is not a complete measure of drilling efficiency.

This is not merely a theoretical distinction. Published drilling studies have documented cases where wells continued to achieve relatively high ROP while other indicators showed substantially poorer drilling efficiency.[1]

Similar ROP can be produced under very different drilling conditions.

ROP Measures the Result, Not the Mechanism

ROP is valuable because the economic objective of drilling is closely connected to footage and time.

But ROP does not explain how that footage was achieved.

ROP quantifies drilling speed; it does not independently describe the mechanical condition that produced that speed.

Consider two drilling intervals that both average 200 ft/hr.

In the first interval:

• torque is relatively stable,
• WOB and RPM are operating within a repeatable range,
• energy input is effectively producing new hole,
• and there is little evidence of damaging dynamics.

In the second:

• torque is cycling significantly,
• rotational energy is being stored and released through the drillstring,
• the bit may repeatedly accelerate and decelerate,
• and the same average ROP is being achieved under a strong torsional dysfunction.

The ROP number alone treats these intervals as equivalent.

Mechanically, they are not.

The distinction was demonstrated in the field application presented in SPE-186166.[1] Six wells from the same pad were compared at a common depth while rotary drilling. Some wells experiencing stick-slip retained relatively high ROP despite lower drilling-efficiency values.

One of the important conclusions from that comparison was that simply maximizing ROP could conceal dysfunctional drilling behavior.

That has an important operational implication:

A drilling parameter change should not automatically be considered successful simply because ROP increased.

The response of the rest of the drilling system matters.

Mechanical Specific Energy Adds an Important Dimension

One way to move beyond ROP is Mechanical Specific Energy, or MSE.

MSE combines several drilling parameters to estimate the mechanical energy required to remove a unit volume of rock.

Conceptually, it asks:

How much mechanical work are we putting into the drilling process for the amount of rock we are actually removing?

This makes MSE fundamentally different from ROP.

ROP measures output.

MSE relates that output to mechanical input.

If considerably more mechanical energy is required to maintain the same drilling rate, that can be evidence that the drilling process has become less efficient.

MSE therefore provides an important additional perspective for real-time drilling surveillance.

But it introduces another important lesson:

MSE is not a complete diagnosis either.

SPE-186166 notes that MSE trends can indicate inefficient drilling without uniquely identifying whether the underlying cause is stick-slip, whirl, bit bounce, bit balling, a formation change, poor hydraulics, or another condition.[1]

The same increase in MSE can therefore have several different interpretations.

MSE provides an energy-based view of drilling performance, but formation and dysfunction context are still required to interpret the cause of a change.

Formation Changes the Meaning of MSE

Imagine drilling from a relatively soft interval into a significantly stronger formation.

ROP may decrease.

MSE may increase.

Nothing necessarily went wrong.

More energy may simply be required to remove the stronger rock.

This is why the SPE-186166 methodology incorporated rock-strength information where available and compared MSE behavior with formation strength rather than treating a single MSE threshold as universally meaningful.[1]

Formation context is particularly important in real-time analysis because the same set of surface drilling parameters can produce different outcomes as lithology changes.

The question therefore should not simply be:

Is MSE increasing?

It should be closer to:

Is MSE increasing more than would reasonably be expected from the formation and the current operating conditions?

That is a more useful engineering question.

It also illustrates a broader principle in drilling analytics:

Absolute measurements become more meaningful when they are interpreted relative to the physical environment in which they were generated.

MSE Still Does Not Tell You Which Dysfunction Is Present

Suppose ROP begins falling while MSE rises.

Increasing WOB might appear to be an obvious response.

But that could be exactly the wrong response if the system is already experiencing stick-slip.

SPE-186166 gives a simple illustration of this distinction.

For stick-slip, a common mitigation direction when no active mitigation controller is available is to reduce WOB and increase RPM.

For whirl, the appropriate direction may be different—increasing WOB and reducing RPM can move the bit toward a more stable operating condition.[1]

Those are not universal prescriptions for every BHA and every well. They demonstrate the larger point:

Different dysfunctions can require opposing parameter changes.

A metric that tells us only that drilling has become inefficient is therefore not enough.

We need evidence about how the system has become inefficient.

That evidence can come from the behavior of torque, WOB, differential pressure, ROP, bit aggressiveness, formation information and other relevant measurements.

Signal Behavior Can Matter More Than the Average

Consider torque.

Suppose the average surface torque over a one-minute interval is 15,000 ft-lbf.

Now consider two traces.

Interval A

Torque remains between approximately 14,500 and 15,500 ft-lbf for most of the interval.

Interval B

Torque repeatedly cycles between 8,000 and 22,000 ft-lbf.

The average may still be approximately 15,000 ft-lbf.

But these are not equivalent drilling conditions.

Averages discard information about how the signal behaves.

This is why real-time dysfunction analysis often evaluates both the magnitude and movement of drilling measurements.

The methodology described in SPE-186166 used moving windows to identify whether selected parameters were:

• increasing,
• decreasing,
• relatively constant,
• or erratic.[1]

Linear fitting was used to characterize trends, while variability within a window provided additional information about erratic behavior.

That creates a more informative question than:

What was average torque?

The better question becomes:

What was torque doing?

Average values can conceal drilling dysfunction; signal behavior provides information that ROP and averages alone do not.

A Published Same-Pad Example

A useful field example appears in SPE-186166.

Six wells on the same pad were evaluated at approximately the same measured depth during rotary drilling.[1]

Several wells had relatively high calculated drilling efficiency.

Two wells showed lower efficiency because stick-slip was detected.

Importantly, ROP remained high.

The published figure includes examples around:

• approximately 200 ft/hr with substantially reduced drilling efficiency,
• approximately 213 ft/hr with detectable stick-slip,
• and approximately 223 ft/hr with high drilling efficiency.

The point is not that 200 ft/hr is inefficient or that 223 ft/hr is efficient.

Those values belong to that specific dataset.

The important observation is that high ROP existed on both sides of the efficiency comparison.

If an engineer had ranked those wells using ROP alone, some of the underlying mechanical differences would have been missed.

Synthetic WOB-RPM operating space illustrating how similar ROP can occur in both efficient and dysfunctional regions.

The Same WOB and RPM Do Not Guarantee the Same Result

Another important observation from the field study was that similar WOB and RPM values did not necessarily produce similar drilling efficiency.

At another depth, two wells operating at similar WOB and RPM showed very different calculated efficiency values.[1]

The authors identified several potential contributors:

• bit condition,
• wellbore tortuosity,
• hole cleaning,
• motor condition,
• and other operational differences.

This is particularly important when building drilling roadmaps from offsets.

It is tempting to identify the fastest offset, retrieve its WOB and RPM, and call those values the optimum.

But the operating point that worked on one well does not exist independently of the rest of the system.

Its outcome depended on:

• the formation,
• the BHA,
• the bit,
• the hole condition,
• drilling history,
• hydraulics,
• directional behavior,
• and the current condition of the equipment.

SPE-186166 concluded that optimal WOB-RPM regions could vary substantially even among wells on the same pad.[1]

The implication is significant:

Offset-well parameters are a starting point, not a universal optimum.

Real-time evidence from the current well still matters.

High ROP Can Create Other Performance Tradeoffs

Drilling efficiency also extends beyond the immediate mechanics at the bit.

Wellbore quality

SPE-196020 examined more than 300 lateral BHA runs and used a tortuosity index to add a quantitative measure of wellbore quality to conventional performance measures.[2]

The paper explicitly notes that traditional metrics such as ROP, total days and number of runs do not fully capture the quality of the wellbore delivered.

The highest-ROP well is therefore not necessarily the best well from a later well-construction or completion perspective.[2]

Excessive tortuosity can contribute to:

• increased and erratic torque and drag,
• poorer hole cleaning,
• casing and liner-running difficulty,
• and other operational complications.

ROP is important.

But ROP and wellbore quality should not be treated as interchangeable objectives.

Hole cleaning

Higher ROP also means a greater rate of cuttings generation.

That does not mean high ROP is inherently bad for hole cleaning.

It means the hydraulic and mechanical system must be capable of transporting the additional solids being generated.

SPE-204125 describes hole cleaning as a process influenced by circulation rate, bit hydraulics, hole angle, pipe movement, rotation and the history of previous operations.[3]

If ROP is increased while circulation capability remains unchanged, the balance between cuttings generation and transport can change.

A parameter change that improves instantaneous ROP should therefore still be evaluated in the broader context of hole condition.

Bit condition

Bit condition introduces another layer.

SPE-205844 demonstrates that changes in ROP can result from formation, dysfunction or PDC wear and therefore should not automatically be interpreted as bit damage.[4]

The reverse is also important.

A bit can continue making acceptable footage while its mechanical condition deteriorates.

Performance surveillance therefore benefits from examining ROP together with quantities related to WOB, RPM, depth of cut, torque behavior and longer-term trends.

The Objective Should Be Sustainable Performance

The operational goal is rarely the highest ROP that can be achieved for the next thirty seconds.

A more useful objective is:

The highest sustainable drilling performance that maintains acceptable mechanical behavior, hole condition and wellbore quality.

That shifts the optimization problem away from a single variable.

Instead of:

Maximize ROP.

the practical objective becomes something more like:

Increase ROP while keeping the system out of significant dysfunction and maintaining acceptable hole and equipment conditions.

That is a more difficult problem.

It is also much closer to the actual engineering objective.

The operational objective is not simply maximum instantaneous ROP, but high sustainable performance within acceptable mechanical and wellbore conditions.

A Practical Real-Time Workflow for Interpreting ROP

When ROP increases significantly, the first reaction should not automatically be to preserve the new operating point.

A structured review can be more useful.

1. Confirm the operational state

Compare drilling with drilling.

Do not mix rotary drilling, slide drilling, reaming, off-bottom circulation and other activities in the same performance calculation.

2. Examine the parameter change that produced the ROP response

What changed?

• WOB?
• RPM?
• flow?
• differential pressure?
• auto-driller set point?

The ROP response is more meaningful when the input change is understood.

3. Evaluate energy efficiency

Review MSE or another relevant energy-based metric.

Did ROP increase while energy per unit rock removed improved?

Or did the system require substantially more energy to produce the additional footage?

4. Inspect drilling dynamics

Look at torque variability and other relevant dysfunction indicators.

Did the faster drilling rate introduce stronger oscillation or instability?

5. Apply formation and depth context

Did the apparent improvement occur at a formation change?

Was the current interval legitimately easier to drill?

Comparisons should be made over geologically and operationally meaningful intervals.

6. Consider the condition of the hole and equipment

Does the operating point remain compatible with:

• hole cleaning,
• bit condition,
• motor condition,
• wellbore quality,
• and other relevant constraints?

7. Watch persistence

A short ROP spike is not the same as sustained improvement.

The parameter combination should remain favorable long enough to determine whether it represents a repeatable operating condition.

A Hypothetical Example

Consider two rotary drilling intervals in the same formation.

Interval A

• ROP: 205 ft/hr
• WOB: 30 klbf
• RPM: 120
• torque: stable
• MSE: relatively stable
• no significant evidence of torsional dysfunction

Interval B

• ROP: 215 ft/hr
• WOB: 40 klbf
• RPM: 85
• torque: strongly oscillatory
• MSE: elevated
• evidence consistent with developing stick-slip

If performance is ranked only by ROP:

Interval B wins.

If the full drilling response is considered:

the conclusion is much less obvious.

The additional 10 ft/hr may have been obtained by moving the system into a less mechanically stable operating region.

An engineer may determine that the faster operating point is acceptable.

Or the engineer may adjust WOB and RPM to seek a slightly lower instantaneous ROP with substantially more stable drilling.

The important point is that the decision is now based on engineering evidence rather than a single performance number.

Benchmark the Process, Not Just the Best ROP

Historical offset data remains extremely valuable.

But instead of asking:

What was the highest ROP on the offset?

a more useful analysis asks:

Under what operating conditions was high ROP repeatedly achieved without significant dysfunction?

Then:

Did those conditions also produce acceptable bit life, hole condition and wellbore quality?

That creates a much stronger benchmark.

It turns the offset from a list of parameter values into evidence about an operating envelope.

Depth-aligned traces compare the current well (orange) with the offset well (blue). Despite broadly similar WOB, RPM, flow rate, and pressure, the current well achieved higher ROP and lower total MSE with a different bit design—showing why offset benchmarking should evaluate the operating system, not ROP alone.

ROP Remains Essential—It Just Should Not Stand Alone

None of this reduces the importance of ROP.

Making hole efficiently remains one of the central objectives of drilling optimization.

ROP is immediate, understandable and economically meaningful.

The problem begins when ROP is asked to answer questions it was never designed to answer.

ROP cannot tell us by itself:

• how efficiently energy reached the rock,
• whether the drillstring was dynamically stable,
• whether the formation changed,
• whether the bit is degrading,
• whether hole cleaning remains adequate,
• or whether the wellbore being delivered is of acceptable quality.

Those questions require other measurements and engineering context.

The most useful interpretation is therefore not:

High ROP = good drilling.

Nor is it:

High ROP = aggressive or inefficient drilling.

It is:

High ROP is valuable when the surrounding evidence shows that the drilling system is achieving it efficiently and sustainably.

That is the difference between monitoring drilling speed and understanding drilling performance.

---

References

1. Ambrus, A., Ashok, P., Chintapalli, A., Ramos, D., Behounek, M., Thetford, T. S., and Nelson, B. A Novel Probabilistic Rig Based Drilling Optimization Index to Improve Drilling Performance. SPE-186166-MS, SPE Offshore Europe Conference & Exhibition, Aberdeen, United Kingdom, 2017.

2. Shahri, M., James, M., Vasicek, A., De Napoli, R., White, M., Behounek, M., D'Angelo, J., Ashok, P., and van Oort, E. Case Studies: Optimizing BHA Performance by Leveraging Data and Advanced Modeling. SPE-196020-MS, SPE Annual Technical Conference and Exhibition, Calgary, Alberta, Canada, 2019.

3. Ashok, P., D'Angelo, J., Ramos, D., Yi, M., Thetford, T., Younk, N., Bohlander, S., Shahri, M., and Behounek, M. A Probabilistic Belief System to Track the Cleanliness of a Hole in Real-time. SPE-204125, SPE/IADC Drilling Conference, 2021.

4. Witt-Doerring, Y., Pastusek, P., Ashok, P., and van Oort, E. Quantifying PDC Bit Wear in Real-Time and Establishing an Effective Bit Pull Criterion Using Surface Sensors. SPE-205844-MS, SPE Annual Technical Conference and Exhibition, 2021.