Water Well Drilling Rig Fuel Consumption: What It Really Burns per Hour

A driller in Ghana sent me his fuel log in August. Two weeks, one 65 kW rig, ninety-six hours on the clock. He was burning 14.2 litres an hour and he wanted to know if the engine was sick.

It wasn’t. He was opening a 12-inch hole through weathered granite with a set of buttons that had done maybe 400 metres too many, and roughly two hours of every shift went to idling while the crew moved casing and waited for the water truck.

The engine was healthy. The number was telling him something else — and that is the whole problem with fuel figures. Almost nobody quotes them properly, so everybody guesses, and the guesses are usually wrong in the expensive direction.

Below is the version I give to customers who ask. It covers what a water well rig actually burns, how to compute it for your own machine, and where the money really leaks.

The Short Answer: Litres per Hour by Rig Class

While the bit is turning and the pump or compressor is working, a water well drilling rig burns roughly this much diesel:

Rig class	Engine power	Burn while drilling	Per 8-hour shift
Portable / trailer-mounted	30–45 kW	5–8 L/h	40–65 L
Crawler water well, light (e.g. WD-W260)	65 kW	9–13 L/h	70–105 L
Crawler water well, heavy (e.g. WD-W600)	129 kW	17–24 L/h	135–190 L
Heavy DTH / deep rotary	250 kW+	30–45 L/h	240–360 L

Those ranges match what other equipment suppliers publish: small to medium rigs are commonly quoted at 40–120 litres per eight-hour shift, and small units at 5–10 litres per hour. If your log sits inside the band for your engine size, your machine is normal. If it sits 30% above it, something in the list further down is costing you money.

Where Those Numbers Actually Come From

You do not need a dyno. You need three inputs and one formula:

Litres per hour = engine kW × load factor × specific fuel consumption

Specific fuel consumption for a modern diesel is about 0.21–0.25 litres per kWh of engine output. Older mechanical engines sit nearer 0.26. The load factor is the part everyone forgets: a rig almost never runs at rated power.

• 65 kW × 0.65 load × 0.22 = 9.3 L/h
• 129 kW × 0.65 load × 0.22 = 18.4 L/h
• 250 kW × 0.65 load × 0.22 = 35.8 L/h

Now change the load factor to what actually happens on site and the number moves a lot:

Activity	Load factor	65 kW rig	129 kW rig
Collaring and spudding	0.70–0.80	10–11 L/h	20–23 L/h
Straight rotary drilling	0.60–0.70	8.5–10 L/h	17–20 L/h
Reaming or opening hole	0.65–0.75	9–11 L/h	18–21 L/h
Tripping rods	0.30–0.40	4–6 L/h	8.5–11 L/h
Idling between operations	0.10–0.20	1.5–3 L/h	3–6 L/h

That table is why two contractors with identical rigs report figures 40% apart. One drills; the other drills, trips, waits and idles. The clock does not distinguish between them, but the fuel log does.

The Compressor Is a Second Engine You Forgot to Budget

On a mud rotary job, the rig is the only diesel engine on site apart from the water truck. On a DTH job there is a second engine, and it is not small.

A towed compressor delivering around 8.5 m³/min at 8.5 bar typically carries a 75–90 kW engine, and it runs at high load for hours because air demand does not ease off. Run the same formula and you get 13–16 L/h. A 21 m³/min unit with a 160 kW engine lands nearer 26–30 L/h. On many DTH water well jobs the compressor burns as much as the rig, sometimes more.

This matters when you compare methods on paper. A DTH package that looks cheap per metre in labour terms can lose that advantage entirely on fuel if the air volume is oversized for the hammer. The right question is not “how much air can this compressor make” but “how much air does this hammer need at this pressure” — which is a separate calculation, covered in our guide to DTH hammer air requirements.

Fuel per Metre: The Number That Decides the Job

Nobody buys diesel by the hour. You buy it per metre of hole, and that depends on penetration rate far more than on engine size. Take a 65 kW rig burning 12 L/h:

Penetration rate	Fuel per metre (rig only)	Fuel for a 200 m hole
1.5 m/h	8.0 L/m	1,600 L
3 m/h	4.0 L/m	800 L
5 m/h	2.4 L/m	480 L
8 m/h	1.5 L/m	300 L

Put a price on it and the picture sharpens. At an illustrative US$1.40 per litre — substitute your own delivered price, because it varies enormously by country and by whether you are buying at a pump or from a tanker — 200 metres at 3 m/h costs about US$1,120 in diesel. The same hole at 1.5 m/h costs US$2,240. Twice the fuel for the same metreage, and the only thing that changed was how fast the bit cut.

Add the compressor on a DTH job and roughly double these figures. This is exactly why our breakdown of water well drilling cost puts fuel in the variable column rather than the fixed one.

Four Things That Move the Number More Than the Machine

1. Bit condition

A dull bit does not stop drilling. It just stops cutting efficiently, and the difference goes straight out of the exhaust. When button flats widen past about a third of the button diameter, penetration drops and fuel per metre climbs — in my experience by 20–30% before the driller notices anything except “the ground got harder”. The measurement and the fix are in our button bit grinding guide. It is the cheapest fuel saving available.

2. Air volume matched to the hammer

Too little air and the cuttings are reground under the bit, which doubles the work per centimetre. Too much air and you are heating the atmosphere. Both show up as fuel burn with nothing to show at the collar.

3. Hole diameter

Going from 8-inch to 12-inch hole does not raise fuel by 50%. It raises torque, cuttings volume and the air or mud required to clear them, and those compound. If the completion only needs 8-inch, drill 8-inch. This is the same diameter-versus-depth trade-off that decides real capacity, which we worked through in how deep a water well rig can actually drill.

4. Idling and tripping

An idling 65 kW rig burns 2–3 L/h doing nothing. Two hours of that per shift, 250 shifts a year, is 1,000–1,500 litres — a set of bits, or a service kit, spent on noise. Shut it down when the crew is handling casing. The starter is cheaper than the fuel.

How to Measure Your Own Burn in Three Days

Published figures are a planning tool. Your own log is the truth, and it takes three days to build.

1. Fill to full at the start of the shift, at the same pump, at the same time of day. Note the hour meter reading.
2. Fill to full at the end of the shift from the same pump. Litres added divided by hours run is your litres per hour.
3. Log metres drilled separately from hours run, and log idle hours too. Litres divided by metres is the number that matters commercially.

Shift	Engine hours	Idle hours	Metres	Litres	L/h	L/m
Day 1	9.0	2.0	21	104	11.6	4.9
Day 2	9.5	1.2	28	108	11.4	3.9
Day 3	8.5	0.8	31	96	11.3	3.1

That is a made-up but realistic set of rows, and it shows the pattern you are looking for: the hourly burn barely moves while the per-metre cost falls by a third. If your hourly burn is stable and your per-metre number is drifting up, the problem is not the engine. It is the bit, the ground, or the way the hole is being made.

Diesel Quality and Storage: The Slow Cost

Fuel that costs 8% less per litre and clogs a filter every fortnight is not cheaper. In hot, humid climates the common failures are predictable:

• Water and sediment in the tank, usually from condensation and from drums stored on their side. Drain the water trap daily, and the tank sump monthly.
• Filter loading from dirty supply. A restricted filter raises injection pressure and cuts power exactly when you are drilling the hard interval.
• Microbial growth in biodiesel blends left standing. It forms a mat on the tank floor and travels to the injectors.
• Injector and pump wear from abrasive fines. This is the expensive one, and it shows up as smoke and lost power long before it shows up as a breakdown.

None of this is exotic. It is the same discipline covered in the DTH rig maintenance checklist, applied to the fuel side instead of the hammer side.

If Fuel Cost Is the Deciding Factor

Three practical rules, in the order they save the most money:

1. Right-size the rig. A 129 kW machine doing the work of a 65 kW machine burns 40–60% more diesel for the same metreage. Buy the smallest class that holds your depth at your diameter in your ground — not the one that looks more capable in a brochure.
2. Right-size the air. Match compressor output to hammer demand at the working pressure. Oversized air is the single most common hidden fuel cost on DTH water well work.
3. Consider electric where the grid is real. Mains power at a stable site cuts fuel to near zero and cuts noise with it. It stops making sense the moment you have to gen-set the power or move every three weeks — the trade-off is the same one we set out in DTH versus rotary for method choice.

If you are still comparing machine classes, the full range is on our drilling rigs page, and the bits, rods and hammers that affect burn rate are on drilling tools.

Two Budgets Side by Side

Abstract figures get argued about. Two jobs I quoted this year make the pattern concrete. Both are real configurations; the fuel numbers follow from the arithmetic above, not from a meter reading.

Item	Village borehole, 150 m	Irrigation well, 250 m
Hole size	8-inch (200 mm)	12-inch (305 mm)
Method	Mud rotary	DTH with towed compressor
Rig	65 kW crawler	129 kW crawler
Average penetration	4 m/h	3 m/h
Drilling hours	~38	~83
Rig burn	12 L/h → 456 L	20 L/h → 1,660 L
Compressor burn	—	14 L/h → 1,160 L
Trips, idling, setup	~90 L	~200 L
Total diesel	~550 L	~3,020 L
Fuel per metre	~3.7 L/m	~12.1 L/m
At US$1.40/L	~US$770	~US$4,230

Three times the fuel per metre, and none of it is waste. The second hole is deeper, wider and drilled in harder ground with air. What the table shows is where the money goes, which is the argument for quoting fuel as a line item rather than burying it in a day rate.

It also shows why a “cheap” rig can be expensive. If the 129 kW machine had been sold into the village job, it would have burned 20 L/h to make hole that a 65 kW rig makes at 12 L/h. Same metreage, 65% more diesel, forever.

Fuel Logistics: How Much to Hold on Site

The calculation is the easy part. Keeping diesel on a remote site without losing it is the operational part, and it affects your real cost per litre more than most people admit.

• Size the tank to one week, not one month. Long storage means water, sediment and microbial growth, and it means more capital sitting in a tank that can be stolen.
• Use a mechanical flow meter on the dispenser. It converts “we think we used about a hundred litres” into a number you can compare with the engine hour meter. Most fuel discrepancies disappear the week a meter is installed.
• Record every fill against the hour meter. Two columns in the site book. A sudden 15% jump is your earliest warning of an injector problem, an air leak, or a hose pulled off the tank.
• Keep drums off the ground and out of the sun, bung up, and never store in a container that has held a different product. Contamination shows up as filter clogging two weeks later.

On multi-rig sites the numbers add up fast. A single 65 kW rig at 100 litres a shift, running 25 shifts a month, is 2,500 litres a month — enough that a 2% variance is worth chasing.

Questions I Get Asked About Rig Fuel

How much fuel does a water well rig use per day?

For a 65 kW crawler rig, plan 70–105 litres per eight-hour shift. For a 129 kW machine, 135–190 litres. Add the compressor if you are drilling with air: a 8.5 m³/min unit adds roughly 100–130 litres per shift.

Does a DTH rig burn more fuel than mud rotary?

Yes, usually 60–100% more for the same hole, because you are running a compressor as well as the rig. That extra burn often buys penetration two to four times faster in hard rock, which is why the per-metre number can still come out lower. Compare per metre, never per hour.

How do I calculate fuel cost per metre?

Litres per hour divided by metres per hour, multiplied by your delivered price per litre. Log all three for a week before you quote a job. Estimates from a brochure will be wrong by enough to matter.

Is a smaller engine always cheaper to run?

Only if it can hold the penetration rate. An undersized rig that labours at 1 m/h in hard ground can burn more per metre than a larger one cruising at 4 m/h. Engine size is not the variable that matters — fuel per metre is.

If you send me your engine size, hole diameter, ground description and the hourly rate you are getting, I will tell you whether your burn is normal or whether there is money leaking somewhere in the chain.