Drilling performance · rig time

NPT in drilling: nonproductive time, explained

Nonproductive time (NPT) in drilling is rig time spent on anything that does not move the well forward as planned: repairing failed rig equipment, fishing, regaining well control, curing losses, or waiting on weather, materials, orders or third-party services. It is usually reported as a share of total rig time, NPT % = NPT hours ÷ total rig hours × 100, and costed at the daily spread rate, NPT cost = NPT hours ÷ 24 × spread rate. There is no single industry definition, so the same well can show different NPT under different companies' rules; what makes NPT useful is logging it consistently, with a cause, on the daily drilling report. Time lost inside planned operations, such as slow connections or trips, is not NPT but invisible lost time, and it has to be found by benchmarking.

1. What counts as NPT

The basic test is whether the time was part of the well plan. Drilling ahead, planned trips, running casing and cementing, logging and BOP tests are productive time even when they take a long time. Time spent dealing with something that went wrong, or waiting for something that should already have been there, is nonproductive. On the IADC daily drilling report the time is still logged under the operation the crew was doing, for example code 8 for rig repair or code 19 for fishing, and then flagged as NPT with a cause; see IADC daily drilling report codes for the codes themselves.

Companies draw the line in different places. In a 2010 Drilling Contractor survey of the subject, Occidental's drilling manager described a broad definition, under which anything outside the original well plan counts as NPT, and split it into "hard" NPT tied to a specific equipment failure and less visible NPT, such as an extra trip caused by an underperforming bit or hole conditions. Chevron's vice president of drilling and completions said his company deliberately logged more events as NPT so that they would be flagged for analysis, and that NPT was a way to find improvements rather than a performance number. The practical lesson is that NPT figures are only comparable when they are logged under the same rules.

2. The main causes of NPT

Which group dominates depends on the rig and the field. In the same 2010 Drilling Contractor article, an internal Chevron study found that BOPs and top drives accounted for 51% to 75% of equipment-related NPT across two deepwater data sets, while on land rigs power generation and fluids equipment were described as the main trouble spots. Downhole problems such as stuck pipe and lost circulation are driven by the well itself: pore pressure, fracture gradient, hole cleaning and how close the mud weight and ECD run to the limits.

3. How to calculate NPT percentage and cost

Two formulas cover most reporting:

• NPT % = NPT hours ÷ total rig hours × 100
• NPT cost = NPT hours ÷ 24 × daily spread rate

The spread rate is the full daily cost of keeping the operation going: the rig day rate plus the services, rentals and personnel that keep charging while the rig is stopped. Using the rig day rate alone understates the cost.

Worked example

A land well takes 30 days from spud to rig release, so total rig time is 30 × 24 = 720 hours. The daily drilling reports record these nonproductive events:

NPT % = 86.4 ÷ 720 × 100 = 12.0%. With an illustrative spread rate of $60,000 a day, the cost is 86.4 ÷ 24 × $60,000 = $216,000. The stuck-pipe event alone is 41.5 ÷ 86.4 = 48% of the NPT, which is where the analysis should start. These figures are an arithmetic illustration, not a benchmark.

4. Invisible lost time

Some of the most expensive lost time never appears as NPT, because the operation was planned. A trip that took twice as long as the best crew's trip, or connections that take a few minutes longer than they should, are logged as productive time. This is usually called invisible lost time (ILT). Because it is spread across hundreds of short operations, conventional 15- or 30-minute reporting misses it.

The arithmetic is simple and the effect is large. At a 2013 IADC conference, a Halliburton drilling optimisation specialist pointed out that one extra minute per connection in a 10,000-ft section adds 100 minutes to the operation, and described a case where day crews averaged 11 minutes per connection and night crews 14 on a 12¼-in. section; after a crew competition connections fell to 8½ minutes, saving 172 minutes over the section. ILT is found by timing repeated operations, such as connections, tripping speed in stands or feet per hour, and casing running in joints per hour, and comparing them with the best performance on offset wells or the same rig.

5. How to reduce NPT

• Log it at source, with a cause. Record each NPT event when it happens with the operation code, the cause, the equipment involved and who was responsible. "Waiting" or "repair" on its own cannot be analysed.
• Investigate the small events too. In the Chevron study cited above, up to 94% of one contractor's NPT incidents over two years had no root cause analysis because they fell below a 12-hour threshold. Frequent short failures add up.
• Separate maintenance from repair. Planned maintenance (code 7) and reactive repair (code 8) need to be kept apart, or equipment reliability cannot be measured.
• Use offset wells before spud. Review where previous wells in the field lost time: stuck pipe depths, loss zones, tight hole, and the mud weights and ECDs that worked.
• Watch the hydraulics. Many lost-circulation and well-control events start with ECD too close to the fracture gradient or mud weight too close to pore pressure; see annular pressure loss and kill sheet calculations.
• Plan logistics around the critical path. Waiting on casing, cement, crews or approvals is avoidable NPT; track it as carefully as equipment failures.
• Benchmark ILT. Time connections and trips and compare crews and wells, so that the hidden lost time is visible as well as the NPT.
• Read the contract. Daywork contracts often allow a set number of repair hours at the full rate before repair time is paid at a reduced rate or not at all. The exact terms vary by contract, so check how your rig repair time is paid and make sure the daily report supports it.

6. In DrillX

DrillX daily drilling reports use IADC-style time logs. DrillX checks each report as you type, flags lost time and catches errors such as depth at 24:00 shallower than at 00:00, or footage with no drilling time logged. The rig fleet view shows each rig's latest position from its daily report, and NPT insights show where rig time is being lost. DrillX also includes calculators such as a kill sheet, ECD and string volumes. DrillX opens soon; email info@drillx.app for a demo or early access.

Sources and further reading

• Drilling Contractor, Rig NPT: the ugly truth (September/October 2010): Chevron and Occidental views on NPT definitions, Chevron equipment-NPT study, root cause analysis threshold.
• Drilling Contractor, Automated rig activity analysis offers more precise method for reducing NPT, invisible lost time (November 2013): NPT and invisible lost time figures from the IADC Critical Issues Asia Pacific conference.
• IADC, Definitions of the 34 Main Codes of the IADC DDR Plus (2019).

Reference summary only. The worked example is illustrative arithmetic. NPT definitions differ between companies and contracts; use your own reporting rules and contract terms.