Focus on Invisible Lost Time while Managing Non Productive Time for Real Drilling Performance Improvement

My challenge: how many managers in upstream oil and gas companies know the right questions to ask their drilling manager (department)? Poor practices (bore hole surveying bad practices are rampant) and unacceptable well drilling times (Europe land drilling is asleep at 250 feet per day versus super drillers on land in USA and offshore Thailand at 2000 feet per day) do not get challenged by managers as companies expose themselves to risks and lost value (undrillable relief wells, inadequate reservoir definition) and higher well costs (time really is money plus accelerated production).

The fallacy of management focus on Non Productive Time (NPT)

Almost all operators use percentage Non-Productive Time (NPT) as a measure of efficiency, concluding that a well drilled with a low % NPT represents a “better” performance than a well with a high % NPT. This, however, is not necessarily true. If two identical wells are drilled with 10 days NPT where the first well took 100 days in total resulting in 10% NPT and the second was drilled more aggressively in just 50 days, resulting in 20% NPT. The 20% NPT well represents the better drilling performance despite the higher % NPT figure proving that % NPT is meaningless standalone.

A guaranteed way to reduce % NPT is simply to drill slowly thus increasing well cost while delaying hydrocarbon production and to plan / report unscheduled events into the normal drilling duration. Benchmarking data provides numerous examples of relatively inefficient wells displaying low NPT values, suggesting creativity in reporting stopped operations off the critical path.

The issue is that the numerator and denominator both vary independently; this can be solved by reporting NPT in terms of ‘per foot / meter’ in the same way that drilling speed is often reported as ‘Days per foot / meter’. As the length of a foot / meter does not change a low ‘NPT days per foot / meter’ will always represent a better performance than a higher ‘NPT days per foot / meter’.

This, however, only provides a useful measure if NPT is, in fact, capturing all the inefficiency in the drilling process. If it is only capturing some part of the total inefficiency, then the NPT metric is of limited use in measuring total performance.

 Who really understands and admits to Invisible Lost Time (ILT)

There is a better measure of drilling efficiency than NPT, it is ILT. Determining ILT requires a reference performance against which to measure the gap from current performance. A realistic measure of drilling performance or efficiency is to measure and report both NPT and ILT using a single number that sums both quantities. Who is aware of any operator directly measuring and reporting ILT at present?

Some operators set a benchmark for themselves by using the fastest times they have ever achieved for each well section and adding these to provide a target that is their Best-of-the-Best (BOB) well. Its weakness is that this technique measures against internal results without external reference or consideration of potential levels of performance. Results can be achieved that are very close to the BOB composite while falling some way behind the Best-in-Class (BIC) operator leading to the drawback of complacency.

Using benchmarked BIC as a target satisfies the performance measure needs of being challenging as well as real; it has been achieved by others. Unfortunately it does not necessarily reflect the complete potential performance because it is measuring against an achieved performance. However, it does provide a real measure of relative drilling performance or efficiency.

Technical Limit (TL) is a more challenging reference level that is the ‘time is the time it will take to drill a theoretical well assuming a flawless operation on the basis of current knowledge and design technology for all involved systems’ (David Bond and Phil Scott). TL is derived by analysis of historic well data and taking into account BOB data, BIC data and the opportunities team members perceive exist based on their experience.

Maximum Theoretical Performance (MTP) is a calculation of the minimum time a well could possibly be drilled and is calculated from clearly defined physical factors that constrain the drilling time (Ford Brett); viz. rock strength, operational limits, set rates for standard operations, number of casing strings, hole sizes, etc. MTP is the ultimate means to ascertain the real gap between current performance and what is theoretically possible. This gap realistically defines a real operational efficiency ratio in drilling. The challenge is to reasonably and transparently calculate the MTP value for any given well or series of wells.

The objective and advantage of calculating the MTP from the physics for drilling a well is that the result avoids human judgment (used in TL), thus providing a very transparent value against which to measure drilling performance and against which a real drilling efficiency ratio can be calculated.

Real drilling performance requires transparent goals based on best performance.

Here is the list, understand and choose the terms on which your drilling team is willing to compete. Complacency will result in lack of performance and loss of value. Aggressiveness, in a risk managed manner, will lead to maximum results and the greatest opportunity to be a drilling winner.

This post is an extraction from a paper we published: True Lies: Measuring Drilling and Completion Efficiency. John P de Wardt, DE WARDT AND COMPANY; Peter H Rushmore, Retired; Phillip W Scott, Technical Limit Engineering with support from Ford Brett, PetroSkills. SPE 178850 March 2016.