Field Operations
LACT Units: Where the Lease Meter Pays the Royalty Check
A lease automatic custody transfer unit, called a LACT unit for short, is the equipment that measures oil as it leaves a lease and enters a pipeline. It sits between the lease tanks and the pipeline, at the point where the oil changes hands. Every barrel that passes through it becomes part of the sales record. That record decides how much the operator gets paid and how much the mineral owner gets paid. A LACT unit is a compact skid of pipe, valves, and instruments. It does in minutes what a gauger used to do by hand over hours. This article explains what is inside a LACT unit and why its numbers matter.
What a LACT unit does
Before LACT units, oil changed hands on the word of a pumper and a gauger. A gauger climbed the tank, ran a tape down to the oil, read the temperature, and wrote down a number. Buyer and seller trusted that number. The oil was then pumped or dumped into a truck or pipeline, and the paper record went with it.
A LACT unit does the same job without the climb. It measures the volume of oil that flows, checks how much water and sediment ride along with it, and records the result. The recording runs continuously while the unit is dumping, and the totals become the official record of the sale.
LACT stands for lease automatic custody transfer. Custody transfer is the moment ownership of the oil passes from one party to another. On most leases that moment happens when the oil leaves the tanks and enters the pipeline. That meter reading is the number the buyer and the seller settle on. That is why the equipment is built to a standard and checked on a regular schedule.
The parts of a LACT unit
A LACT unit is a skid of pipe with a handful of parts bolted together. Each part has one job. Know the parts and you can spot trouble when something stops working.
The run starts at the dump valve. The dump valve opens to let oil out of the tanks and closes when the run is done. Behind it sits the strainer, which catches sand, scale, rust, and other solids before they reach the meter. Crude is dirty stuff, and a chunk of rock through the meter can cost a day of production.
Next comes the meter, the heart of the unit. Most LACT units use a positive displacement meter, which counts fixed volumes of oil as they pass through. The count is the gross volume of the run. Near the meter is the prover connection, a set of valves and fittings where a prover is hooked up to test the meter against a known volume.
The automatic sampler draws a small, steady sample of the oil while the unit is dumping, so the sample represents the whole tank, not just the start or the end. A BS&W monitor, short for basic sediment and water, reads how much water and solids are mixed into the crude as it flows. If the oil is too wet, the unit diverts the flow back to the tanks instead of to the pipeline.
The meter factor and proving
A meter does not read perfectly forever. Temperature, pressure, viscosity, and wear all change how a meter measures. The meter factor is the correction that brings the meter back in line with reality. It is the ratio of the true volume to the volume the meter reports.
To find the factor, the unit is proved. A prover is a section of pipe with a known internal volume and a detector. The oil is diverted through it, and the meter reading is compared with that known volume. If the meter reports 100 barrels and the prover holds 99, the meter factor is 0.99.
The factor is applied to every reading until the next proof. Proving follows a schedule set by contract, by the state agency, or by the buyer. A meter that is not proved is a meter that no one trusts, and an unproved meter can turn into a dispute at settlement time.
Sampling and BS&W adjustments
The meter measures the whole stream, but not all of the stream is oil. Crude out of a tank usually carries some water and sediment with it. The sampler and the BS&W monitor figure out how much. That amount is subtracted from the gross volume to get the net volume of oil sold.
The sampler bottle is sealed and sent to a lab, or tested at the site, and the result comes back as a BS&W percentage. The gross meter volume is multiplied by the meter factor, corrected for temperature and pressure, and then reduced by the BS&W share. What is left is the net barrel figure on the sales ticket.
The water and sediment are separated out and sent back to the storage tanks or to the water disposal system. The older way to get the same numbers is tank gauging, done by hand, and it is still used on leases without a LACT unit.
Why accurate measurement matters
The numbers a LACT unit produces are money. Royalties are paid on the volume of oil sold, and the volume on the ticket is the volume the royalty check is based on. If the meter reads low, the operator gets paid for less oil than the lease produced. If it reads high, the buyer pays for oil that never reached the pipeline. Either error puts the operator and the mineral owner at odds.
The same numbers feed state production reports, tax filings, and the buyer's inventory. One error in the field can ripple through every office that touches the sale. That is why the record keeping matters as much as the hardware. The sales ticket that closes the run ends up in ticket software like OpsFlo, where the field numbers become the office record.
State agencies such as the Texas Railroad Commission have measurement rules that govern how LACT units are proved and how volumes are reported. Buyers and sellers also set their own terms in the purchase contract. A unit that is kept clean, proved on schedule, and sealed against tampering is the surest way to keep the royalty check honest. The meter on the lease is a small piece of equipment with an outsize job. It is the official witness to every barrel that leaves the lease.
Sources and further reading
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