Crude oil is not automatically ready for sale just because it has reached the surface.
Before a producer can be paid for the oil, the fluid normally needs to be separated, treated, measured, sampled, and transferred to a purchaser or transportation system.
That transfer is important because ownership of the crude is changing.
The producer wants credit for every barrel of actual oil delivered.
The purchaser does not want to pay crude oil prices for water, sediment, free gas, or measurement error.
A LACT unit helps handle this transfer automatically.
LACT stands for Lease Automatic Custody Transfer.
A LACT unit measures crude oil as it moves from a production facility into a sales pipeline or another receiving system. It can also monitor oil quality, collect representative samples, correct measured volumes, and reject oil that does not meet the required sales specification.
For production operators, understanding the LACT unit is important because this is where field production becomes revenue.
A separator problem, heater treater problem, tank issue, pump problem, or bad instrument can eventually appear as a sales problem at the LACT.
What Does LACT Stand For?
LACT means Lease Automatic Custody Transfer.
Each part of the name describes the purpose of the system.
Lease refers to the producing property or facility.
Automatic means the transfer process can operate using instruments and controls rather than requiring someone to manually measure every load.
Custody transfer means ownership or financial responsibility for the crude changes at a defined measurement point.
The LACT unit is therefore much more than a transfer pump.
It is part of the commercial measurement system used to determine how much crude oil has actually been sold.
What Is Custody Transfer in Oil and Gas?
Custody transfer occurs when measured product moves from one party to another.
For example, an oil producer may own the crude inside a lease storage tank.
The crude is then pumped through the LACT unit into a gathering pipeline.
At a defined point, responsibility for that measured oil transfers to the pipeline company or purchaser.
The recorded volume and quality may determine how much oil the producer is credited for.
This makes measurement accuracy extremely important.
A small error repeated every day can become a large financial difference over thousands or millions of barrels.
Why Is a LACT Unit Used?
Crude oil can also be sold using manual tank measurements.
An operator or crude hauler can gauge a tank before transfer, load oil, and gauge the tank again afterward.
The difference helps determine the transferred volume.
That method is still used in some operations.
A LACT unit provides a more automated method.
Instead of calculating the sale mainly from tank level changes, the LACT measures the crude while it is flowing through piping.
It can monitor quality during the transfer.
It can collect a representative sample.
It can automatically divert unacceptable crude.
It can record transfer totals.
This makes frequent or continuous pipeline sales practical.
Where Is a LACT Unit Located?
A LACT unit is normally located near the point where treated crude leaves the producer’s facility.
A typical production facility may contain:
Producing wells
Separators
Heater treaters
Produced water equipment
Oil storage tanks
A LACT unit
A pipeline connection
The exact arrangement varies between facilities.
Some operations store treated crude before sending it through the LACT.
Others transfer oil more directly from the treatment system.
The important point is that the LACT is normally near the final sales point.
What Does a LACT Unit Actually Do?
A typical LACT system may perform several functions during a transfer.
It moves oil toward the receiving pipeline.
It conditions the stream for measurement.
It checks crude quality.
It removes free gas that could interfere with measurement.
It measures liquid flow.
It measures oil temperature.
It collects representative samples.
It records transferred volume.
It can divert oil that fails quality requirements.
It communicates operating information to the facility control system.
All of these functions support accurate custody transfer.
What Is the Basic Flow Through a LACT Unit?
A simplified flow path is easy to understand.
Oil leaves a storage tank or treatment system.
A transfer pump moves the crude into the LACT skid.
The oil passes through conditioning and measurement equipment.
Quality instruments monitor the crude.
A flow meter measures the liquid volume.
A sampler collects small portions of oil during the transfer.
The crude then leaves the LACT and enters the receiving pipeline.
Actual designs vary, but the basic objective remains the same.
Measure clean, stable, saleable crude before it changes custody.
What Is a LACT Skid?
Many LACT systems are built as skid mounted packages.
The major equipment is assembled on a structural base before the package reaches the field.
A LACT skid can include:
Piping
Valves
A pump
A strainer
A gas eliminator
A flow meter
Temperature measurement
A BS and W monitor
A sampler
A diverter valve
A flow computer
Control equipment
Electrical equipment
Building the unit as a package makes installation and testing easier.
Once delivered, the skid is connected to the production facility and the receiving pipeline.
Why Does a LACT Unit Need a Pump?
The crude needs enough pressure to move through the LACT system and enter the receiving pipeline.
The pipeline may already be operating under significant pressure.
The oil also loses pressure as it passes through piping, valves, strainers, meters, and other equipment.
The transfer pump provides the energy needed to overcome these pressure losses.
It draws crude from the source and pushes it through the measurement system.
Stable pump operation also helps provide consistent flow through the meter and sampler.
Can a LACT Unit Operate Without Its Own Pump?
Some systems may already have enough pressure available from upstream equipment.
In those cases, a dedicated LACT pump may not always be required.
However, many lease transfer systems use a dedicated pump because it provides better control over transfer rate and discharge pressure.
A dedicated pump can also make the transfer less dependent on changing upstream production pressure.
What Is BS and W in Crude Oil?
BS and W means basic sediment and water.
It represents material in the crude stream that is not considered saleable crude oil.
Water is often the largest part.
Sediment can include small quantities of solids and other unwanted material.
Crude leaving a production facility is rarely completely free of water.
Even after separation and treatment, a small amount may remain dispersed in the oil.
The purchaser therefore needs to know how much of the measured liquid is actually crude.
Why Does BS and W Matter?
Suppose the LACT meter records 1,000 barrels of liquid.
If all 1,000 barrels are saleable crude, the calculation is straightforward.
Now suppose 15 barrels of that measured liquid are water and sediment.
The purchaser does not normally want to pay crude oil value for those 15 barrels.
The measured liquid volume therefore needs a quality adjustment.
Even small percentages matter when large quantities of crude are transferred.
What Is a BS and W Monitor?
A BS and W monitor measures or estimates the water content in the flowing crude stream.
Different measurement technologies can be used.
The instrument sends information to the LACT control system.
If the water content rises above the acceptable limit, the system can prevent the crude from entering the sales pipeline.
This protects the receiving system from off specification oil.
What Happens If BS and W Is Too High?
The crude can be diverted away from the sales line.
Instead of entering the pipeline, the oil may return to a storage tank or another treatment destination.
The exact arrangement depends on the facility.
Operators then need to determine why the oil quality deteriorated.
Possible causes include:
Poor oil and water separation
Low treating temperature
High water production
Heater treater problems
An emulsion
Incorrect vessel levels
Chemical treatment problems
A disturbed tank
Water near the tank outlet
The oil normally needs additional treatment or settling before another transfer attempt.
Why Can Cold Crude Have Higher Water Content?
Temperature affects crude viscosity and water separation.
When oil becomes warmer, its viscosity often decreases.
Water droplets can then move and separate more easily.
Cold oil can hold small water droplets in suspension more effectively.
Emulsions can also become harder to break when temperatures are too low.
For some crude streams, reduced treating temperature can therefore cause higher BS and W at the sales point.
What Is an Oil Emulsion?
An emulsion occurs when tiny water droplets remain dispersed throughout crude oil instead of separating into a clear water layer.
These droplets can be surprisingly stable.
Several factors can contribute.
Agitation can create smaller droplets.
Natural compounds in the crude can stabilize the oil and water interface.
Fine solids can also help stabilize an emulsion.
A separator may remove free water while significant emulsified water remains in the oil.
Heat, chemical treatment, and retention time are commonly used to improve separation.
What Is Off Specification Crude?
Off specification crude does not meet the required quality conditions for transfer.
High BS and W is a common reason.
Other specifications can depend on the purchaser and crude stream.
The term does not necessarily mean the oil has no value.
It means the crude cannot be accepted into the receiving system in its current condition.
The producer normally needs to treat or condition it further.
What Is a Diverter Valve?
A diverter valve directs oil to different destinations.
In a LACT system, acceptable crude goes toward the sales pipeline.
Crude that fails a quality requirement can be diverted back to storage or treatment.
A three way valve can be used for this purpose.
The control system determines which route is open.
This valve is an important barrier between off specification crude and the custody transfer line.
Why Is Free Gas a Problem in a LACT Unit?
A liquid flow meter is designed to measure liquid.
If free gas or air passes through the meter with the crude, the measured volume may become inaccurate.
The meter may interpret part of the gas volume as liquid volume.
That is unacceptable during custody transfer.
The LACT system therefore needs a properly conditioned liquid stream.
What Is a Gas Eliminator?
A gas eliminator provides a place for unwanted gas to separate from the crude before the liquid reaches the meter.
Gas can enter the system for several reasons.
A storage tank may be drawn too low.
Gas can break out of solution when pressure decreases.
Maintenance can introduce air.
Poor pump suction conditions can also create gas problems.
Removing free gas improves measurement accuracy.
Why Can Gas Break Out of Crude Oil?
Crude can contain dissolved gas.
As pressure decreases, the oil may no longer be able to hold the same amount of gas in solution.
Some gas then comes out of the liquid.
This is similar in principle to opening a carbonated drink and allowing dissolved gas to escape.
If pressure falls too much before the LACT meter, gas breakout can interfere with liquid measurement.
Maintaining suitable pressure through the skid helps prevent this.
What Is a LACT Strainer?
A strainer removes debris from the crude stream before the oil reaches sensitive equipment.
Possible debris includes:
Rust
Scale
Gasket material
Sand
Pipe debris
Other solids
These materials can damage a meter or interfere with valves.
The strainer protects downstream equipment.
As material accumulates, pressure drop across the strainer can increase.
How Can an Operator Tell a Strainer Is Plugging?
Pressure readings are useful.
If pressure before the strainer remains relatively high while pressure after it falls, the pressure difference across the strainer is increasing.
Flow may also decline.
The transfer pump may need to work harder.
A growing pressure difference is often an indication that the strainer needs attention.
Operators should compare current readings with normal operating values.
What Type of Flow Meter Is Used on a LACT Unit?
Different meter technologies can be used depending on the crude, required accuracy, flow range, standards, and facility design.
Positive displacement meters have historically been common for crude oil custody transfer.
Other meter technologies can also be used where appropriate.
The important point is that a custody transfer meter must provide accurate and repeatable measurement under the actual operating conditions.
What Is a Positive Displacement Meter?
A positive displacement meter measures liquid by repeatedly moving known quantities through internal measuring chambers.
Oil flow causes internal components to move.
The number of measuring cycles corresponds to a volume.
These meters can provide very accurate crude measurement when operating correctly.
Because internal components interact with the flowing oil, contamination and wear can affect performance over time.
What Is a Meter Factor?
A meter factor is a correction value used to account for the actual performance of the custody transfer meter.
No real meter is absolutely perfect.
Suppose the meter indicates slightly more volume than a trusted reference system.
The meter factor corrects the reported quantity.
This factor is determined through meter proving.
What Is Meter Proving?
Meter proving is the process of comparing the custody transfer meter against a known reference volume.
Oil is passed through the meter and the proving system.
The meter’s indicated volume is compared with the reference.
The result helps determine whether the current meter factor remains valid.
Proving can identify changes caused by wear, deposits, maintenance, or operating conditions.
What Is a Meter Prover?
A meter prover is equipment that provides a known reference volume for verifying meter performance.
Different prover designs exist.
The principle is the same.
Instead of assuming the LACT meter remains accurate forever, the operator periodically compares it with an accepted reference.
This creates confidence in the custody transfer measurement.
Why Would a Meter Factor Change?
Several things can affect a meter over time.
Mechanical wear.
Internal deposits.
Changes in fluid viscosity.
Changes in flow rate.
Temperature changes.
Maintenance work.
Damage.
A stable meter often produces consistent proving results.
A sudden large shift in meter factor should be investigated.
Why Is Temperature Important During Crude Oil Measurement?
Crude oil changes volume as temperature changes.
Warm oil occupies more volume than the same amount of oil at a lower temperature.
That creates a problem if one transfer is measured on a hot afternoon and another on a cold morning.
Custody transfer systems account for temperature so measured volumes can be corrected to an agreed reference condition.
This helps make commercial volume comparisons consistent.
What Is Gross Observed Volume?
Gross observed volume is the measured liquid volume at the actual conditions present during the transfer.
It has not yet received all of the corrections needed to express the final saleable oil quantity.
Temperature and quality corrections can then be applied according to the applicable measurement procedure.
The exact terminology used by companies can vary.
What Is Net Oil Volume?
Net oil volume represents the saleable crude after the required adjustments have been applied.
Water and sediment are removed from the commercial quantity.
Temperature correction can also be applied.
The objective is to calculate how much actual crude oil changed custody.
Modern flow computers perform much of this calculation automatically.
What Is API Gravity?
API gravity is a common oil industry measure related to crude density.
Higher API gravity generally indicates lighter crude.
Lower API gravity indicates heavier crude.
API gravity affects crude classification, transportation, processing, and commercial value.
It can also be part of custody transfer calculations and quality reporting.
Is API Gravity the Same as Crude Quality?
No.
It is only one crude property.
Oil quality can also depend on:
Water content
Sulfur content
Salt
Sediment
Acidity
Metals
Vapor pressure
Other chemical characteristics
Two crude oils with similar API gravity can still have different values and processing requirements.
Why Does a LACT Unit Need an Automatic Sampler?
A single grab sample may not accurately represent thousands of barrels of crude transferred over several hours.
Crude quality can change during the transfer.
An automatic sampler collects many small portions throughout the run.
Those portions are combined into a composite sample.
This sample can then be analyzed to estimate the average properties of the entire transfer.
What Is a Composite Sample?
A composite sample is a combined sample collected from many smaller portions during the transfer period.
Imagine oil quality slowly changes over an eight hour transfer.
One sample taken at the beginning could be different from one taken near the end.
A properly collected composite sample provides a better representation of the entire batch.
Why Must Sampling Be Representative?
A custody transfer calculation is only as good as the sample used for quality determination.
If the sampler collects unusually wet oil, the reported water content can be too high.
If it collects unusually clean oil, the result can be too low.
The sample point and flow conditions therefore matter.
The sampling system should collect material that represents the main flowing stream.
What Is a Sample Pot?
The small samples collected during transfer are stored in a sample receiver, often called a sample pot.
At the end of the transfer period, the accumulated sample can be mixed and analyzed.
The container needs to be clean.
Material left from a previous transfer can contaminate the next sample.
Correct sample handling is part of accurate custody measurement.
What Does the LACT Flow Computer Do?
The flow computer handles much of the measurement and control logic.
It can receive signals for:
Flow rate
Total volume
Temperature
BS and W
Pressure
Pump status
Valve position
Alarms
Sampler operation
The computer can also perform volume correction calculations and store transfer records.
Modern systems may communicate the information to a remote control center or production accounting system.
Can a LACT Unit Run Automatically?
Yes.
Many systems operate automatically based on tank level or other process conditions.
For example, oil may accumulate in a storage tank.
When the tank reaches a selected high level, the LACT transfer sequence starts.
The pump starts.
Valves move into the correct position.
Oil quality is checked.
Acceptable oil flows to the sales line.
When the tank reaches a lower level, the transfer stops.
The actual sequence depends on facility design.
Why Use Storage Tanks Before the LACT?
Storage tanks provide a buffer between production and sales.
Wells produce continuously or intermittently according to reservoir and equipment conditions.
The receiving pipeline operates according to its own conditions.
A storage tank allows oil to accumulate even when the LACT is not transferring.
Tanks also provide additional time for water to settle from the crude.
Can Crude Flow Directly From a Treater Into a LACT?
Yes, certain facility designs can transfer oil with limited storage between treatment and custody measurement.
The suitability depends on process stability and the required operating philosophy.
Without much storage, treatment reliability becomes especially important.
There is less time for water to settle before the crude reaches the measurement point.
Why Does a LACT Unit Need Backpressure?
Maintaining pressure through the measurement section can help keep dissolved gas in the crude.
If pressure falls too low, gas can break out and interfere with the meter.
Backpressure also helps establish stable operating conditions.
A pressure control valve can maintain the required upstream pressure while the crude flows toward the pipeline.
What Is a Backpressure Valve?
A backpressure valve regulates flow so a selected pressure is maintained upstream.
In a LACT system, it can help maintain adequate pressure through the meter and other components.
The valve must be sized for the expected flow and pressure conditions.
A poorly operating valve can cause unstable flow or excessive pressure.
Why Is Stable Flow Important?
Meters and samplers perform best when flow stays within the intended operating range.
Large fluctuations can make accurate sampling more difficult.
They can also place the meter outside its best operating region.
The pump, valves, and pressure controls therefore work together to create reasonably stable transfer conditions.
What Is a Check Valve Used For?
A check valve allows flow in one direction and prevents reverse flow.
After the LACT pump stops, the operator does not want crude from the receiving pipeline flowing backward through the skid.
Backflow can create measurement, contamination, and operating problems.
The check valve helps maintain the intended flow direction.
What Happens If Pipeline Pressure Increases?
The LACT pump needs to overcome the receiving pipeline pressure.
If that pressure rises, the pump must work against greater resistance.
Flow can decrease.
Discharge pressure can increase.
The pump may move away from its preferred operating condition.
If pipeline pressure becomes too high, the unit may be unable to transfer crude normally.
Why Would a LACT Unit Keep Shutting Down?
There are many possible reasons.
High BS and W.
Low source tank level.
High discharge pressure.
Low suction pressure.
Pump problems.
Meter alarms.
Instrument failures.
Valve problems.
Loss of electrical power.
Control system faults.
Emergency shutdown activation.
A shutdown should be treated as useful information.
Repeatedly resetting the unit without understanding the cause can damage equipment or hide a developing process problem.
What Causes Low LACT Pump Suction Pressure?
Possible causes include:
Low tank level
Closed or partially closed valves
A plugged strainer
Cold viscous crude
Restricted suction piping
Gas entering the pump
Poor tank venting
Trying to transfer faster than the suction system can supply
Low suction pressure can lead to unstable pump operation and cavitation.
What Is Pump Cavitation?
Cavitation occurs when pressure inside part of the pump becomes low enough for vapor bubbles to form.
These bubbles later collapse when pressure rises.
The repeated collapse can damage pump components.
Cavitation can also produce unusual noise and vibration.
Poor suction conditions are a common cause.
If a transfer pump suddenly sounds like it contains gravel, cavitation should be considered.
Why Can Hotter Crude Increase Cavitation Risk?
Liquid vapor pressure increases with temperature.
As crude becomes hotter, it can begin forming vapor at a higher absolute pressure than it would when colder.
A pump with marginal suction conditions may therefore cavitate more easily as fluid temperature rises.
This is another reason operators need to consider pressure and temperature together.
Why Would a LACT Pump Lose Prime?
Gas or air can enter the pump suction.
A tank can be drawn too low.
Maintenance can leave air in the system.
A suction connection can leak.
Some pump designs depend on having liquid present before they can move fluid effectively.
Repeated loss of prime usually indicates an underlying condition that should be corrected.
Why Would BS and W Suddenly Increase During a Transfer?
A sudden increase can originate upstream of the LACT.
Possible causes include:
The source tank was disturbed.
Water accumulated near the tank outlet.
The heater treater stopped performing correctly.
Treating temperature decreased.
Chemical treatment changed.
Well water production increased.
A separator level controller malfunctioned.
The LACT instrument may also be faulty.
Operators should investigate the full process rather than assuming the LACT itself caused the wet oil.
Can Water Settle in the Bottom of an Oil Tank?
Yes.
Free water is denser than crude oil.
Given enough time, it tends to settle below the oil.
This creates a water layer near the tank bottom.
If the tank is drawn too low, the outlet may begin pulling fluid near that interface.
BS and W can then rise rapidly.
What Is Tank Bottom?
Tank bottom refers to the material that collects in the lower part of a crude oil tank.
It can contain:
Produced water
Sediment
Rust
Sludge
Heavy hydrocarbons
Other solids
The lowest part of the tank can therefore contain poorer quality material than the main oil inventory.
Operators manage tank bottoms carefully to avoid transferring this material through the LACT.
Why Do Operators Drain Water From Crude Tanks?
Removing settled water prevents the interface from rising toward the sales outlet.
If too much water accumulates, the LACT may reject the crude.
Tank water draining needs to be controlled carefully.
The operator wants to remove water without sending excessive oil into the produced water system.
Sampling and interface measurements can help identify what is being drained.
Why Does Heater Treater Performance Affect LACT Sales?
The heater treater removes water from crude before sale.
If it does not perform correctly, wetter oil reaches the storage tanks and LACT.
The LACT may then reject the oil for high BS and W.
This is an important troubleshooting lesson.
The instrument detecting the problem is not necessarily the equipment causing the problem.
A high water reading at the LACT may begin with a process problem much farther upstream.
Does Increasing Heater Temperature Always Fix Wet Oil?
No.
Low temperature can contribute to poor oil and water separation, but increasing heat blindly is not a good troubleshooting strategy.
The problem may be:
Incorrect retention time
Poor chemical treatment
High fluid rate
An interface control issue
A severe emulsion
Mechanical damage
Changing crude properties
The correct treatment depends on the actual cause.
What Happens When the LACT Rejects Oil?
The control system changes the crude flow path.
Instead of sending the oil into the sales pipeline, it directs the crude to an approved alternate destination.
That may be a storage tank or treatment system.
The oil is not necessarily wasted.
It can often be treated or allowed to settle and then transferred again once it meets specification.
Can a Bad BS and W Instrument Reject Good Oil?
Yes.
Instrumentation can fail.
A dirty sensor, incorrect calibration, wiring problem, or other fault can create an inaccurate reading.
If a sudden high water reading does not match other process information, the operator should verify it.
A correctly collected manual sample can provide an independent comparison.
Why Are Manual Samples Still Important?
Automatic analyzers are useful, but manual sampling provides another source of information.
Suppose the online instrument reports 2 percent water while a properly collected laboratory sample indicates only a very small amount.
That difference suggests the instrument or sample system needs investigation.
Manual samples are also useful when troubleshooting upstream treatment problems.
What Is a LACT Ticket?
A LACT ticket is the record of the custody transfer.
Depending on the system, it can include:
Gross volume
Net volume
Temperature
Meter factor
BS and W
API gravity
Transfer start and stop times
Meter readings
Other measurement information
Older systems may produce physical tickets.
Modern systems often store and transmit the information electronically.
Why Are LACT Records So Important?
They affect revenue and production accounting.
The measured sales quantity can influence:
Producer revenue
Purchaser records
Royalty calculations
Partner allocations
Tax reporting
Production accounting
Inventory reconciliation
Accurate records are therefore commercially important even when the equipment itself appears relatively simple.
Is LACT Sales Volume the Same as Daily Production?
Not necessarily.
Wells may produce continuously while crude is sold only during certain periods.
Storage tank inventory can increase or decrease.
Water can be removed from tanks.
Transfers can cross reporting periods.
A field may produce 1,000 barrels today but sell a different amount because some crude remains in storage.
Production and sales are related but are not always identical.
Why Might Tank Inventory and LACT Sales Not Match?
Possible reasons include:
Tank measurement error
Meter measurement error
Temperature changes
Water drainage
Multiple tank movements
Incorrect starting inventory
Incorrect ending inventory
Leaks
Unrecorded transfers
Timing differences
An unexplained difference that persists should be investigated.
Material balance problems can reveal both measurement and process issues.
What Is Meter Proving Frequency?
Custody meters are proved according to the requirements of the measurement program, applicable standards, contractual requirements, equipment condition, and operating history.
There is no one universal proving interval for every LACT system.
A meter that shows a sudden change in proving results may require additional investigation.
The objective is maintaining confidence that transfer measurement remains accurate.
Can Dirty Crude Damage a LACT Meter?
Yes.
Sediment and debris can wear internal components or interfere with moving parts.
Deposits can also affect performance.
This is one reason crude treatment, strainers, and maintenance are important.
A custody transfer meter should not be ignored simply because it continues producing a number.
Measurement equipment can drift before it fails completely.
What Happens During LACT Maintenance?
Typical maintenance can include:
Cleaning strainers
Inspecting the transfer pump
Checking valves
Testing pressure instruments
Checking temperature measurement
Inspecting the BS and W monitor
Testing the automatic sampler
Servicing the meter
Reviewing meter proving history
Testing alarms and shutdowns
Checking electrical systems
Inspecting piping for leaks
The exact maintenance program depends on equipment design and company procedures.
What Happens If the LACT Meter Fails?
Normal custody transfer may need to stop unless an approved alternate measurement method exists.
If the producer cannot reliably measure the transferred oil, the purchaser may not accept the transfer.
Production can continue into storage temporarily.
Once the available storage becomes full, wells may need to be reduced or shut in.
A relatively small meter problem can therefore affect an entire producing field.
Why Can One LACT Failure Shut In Several Wells?
Many wells can feed one central production facility.
Their oil eventually reaches the same storage tanks and sales system.
If the LACT stops transferring oil, the tanks begin filling.
When storage capacity is exhausted, the incoming production has nowhere to go.
The operator may then need to reduce or stop wells.
This makes the LACT a critical part of production availability.
What Is a Central Delivery Point?
A central delivery point receives crude from multiple wells or production facilities.
Oil can be treated, stored, measured, and transferred from one location.
A large LACT unit may therefore handle production from many wells.
Centralizing the sales point can reduce the amount of duplicate measurement equipment.
The disadvantage is that one central failure can affect a larger amount of production.
Can Several Producers Deliver Into the Same Pipeline?
Yes.
A gathering pipeline can receive oil from many leases and operators.
Each producer needs an approved method of measuring how much crude enters the system.
Custody transfer equipment allows volumes to be assigned correctly.
Without accurate measurement, commercial allocation would become extremely difficult.
What Is Crude Oil Gathering?
Gathering refers to moving crude from individual producing locations toward larger pipelines, terminals, or storage facilities.
Gathering systems are normally closer to the producing wells than major long distance transmission pipelines.
The LACT often marks the point where crude leaves the producer’s facility and enters a gathering system.
Is a LACT Unit Only Used With Pipelines?
No.
Custody transfer measurement can be used in different crude transfer arrangements.
However, LACT units are strongly associated with pipeline sales because they allow oil to be transferred automatically without requiring a truck for every load.
Remote or lower volume leases may still depend on crude hauling.
What Is the Difference Between LACT Sales and Trucked Oil?
With trucked oil, a crude hauler arrives at the facility and loads oil into a tanker.
The amount transferred is measured according to the applicable procedure.
The truck then transports the crude away.
With a pipeline connected LACT, the crude is pumped directly into the gathering or sales pipeline through the custody transfer system.
This allows larger or more frequent transfers without truck traffic.
Why Are Pipeline Sales Often Preferred?
Pipeline transfer can move large quantities of crude efficiently.
It can reduce truck traffic.
It removes dependence on individual truck availability.
It can support automatic transfer.
For high volume production, pipelines can be much more practical than transporting every barrel by road.
The limitation is that pipeline infrastructure needs to exist.
Why Does LACT Flow Sometimes Become Slow?
Possible causes include:
High receiving pipeline pressure
A dirty strainer
Pump wear
A restricted valve
Cold viscous crude
Low tank level
Backpressure valve problems
Meter restrictions
Suction restrictions
Comparing pressures throughout the skid can help locate where the resistance has increased.
Why Is Differential Pressure Useful?
Differential pressure is simply the difference between pressure at two points.
It is extremely useful for identifying restrictions.
If pressure before a strainer is 100 psi and pressure after it is 95 psi, the difference is 5 psi.
If that difference later becomes 30 psi at a similar flow rate, the strainer may be plugging.
The same principle can be applied to other equipment.
What Is SCADA on a LACT Unit?
SCADA allows operators to monitor equipment remotely.
A control room or remote operator may be able to see:
Tank level
Pump status
Flow rate
Transfer totals
Pressure
Temperature
BS and W
Valve position
Alarms
Remote monitoring can reduce unnecessary field visits and allows faster response to abnormal conditions.
It does not replace physical inspection when a field problem needs investigation.
Can a LACT Unit Start Automatically From Tank Level?
Yes.
This is a common operating concept.
The crude tank fills as production enters.
At a selected level, the control system initiates the sales sequence.
The pump transfers crude through the LACT.
When the tank reaches the selected low level, transfer stops.
The tank then begins filling again.
This cycle can repeat without constant operator involvement.
What Is a Permissive?
A permissive is a condition that must be satisfied before the control system allows equipment to operate.
A LACT pump might require:
Adequate tank level
Correct valve positions
Available power
No emergency shutdown
Acceptable receiving pressure
Healthy instruments
No critical alarm
Only after the required conditions are satisfied will the control logic allow the pump to start.
What Is an Interlock?
An interlock automatically prevents or stops an operation when a defined condition occurs.
Examples can include:
High discharge pressure stops the pump.
Low tank level stops the pump.
High BS and W diverts the crude.
A critical instrument failure prevents transfer.
Interlocks help protect equipment, measurement quality, and process safety.
Should an Operator Keep Resetting a LACT Trip?
No.
A trip indicates that the system detected a condition outside normal operation.
Repeated resets without investigation can damage equipment or create a larger process problem.
If the pump repeatedly trips on low suction pressure, check the source tank, valve lineup, strainer, suction pressure, and crude condition.
Do not treat the reset button as the repair.
What Should an Operator Check When the LACT Will Not Start?
Start with basic conditions.
Is there enough oil in the source tank?
Are the correct valves open?
Is electrical power available?
Is the pump ready?
Are any shutdowns active?
Is the receiving pipeline available?
Is BS and W acceptable?
Are important instruments healthy?
Is the system in the correct control mode?
Following the actual flow path often finds the problem faster than immediately assuming there is a control system failure.
What Should an Operator Check When Sales Suddenly Drop?
Compare production, inventory, and sales together.
Check:
Source tank levels
Recent well production
Transfer pump flow
Pipeline pressure
Strainer condition
Valve positions
BS and W diversion
Meter alarms
Transfer run time
Recent shutdowns
If the tanks are filling while sales fall, the problem is probably in the sales system.
If both tank levels and sales are falling, upstream production may have changed.
Why Should a Production Operator Understand the LACT?
Because the LACT connects field operation with money.
A production operator can sometimes prevent a sales interruption by noticing a problem early.
High BS and W may begin with a heater treater issue.
Low LACT flow may begin with a plugging strainer.
Pump cavitation may begin with poor tank management.
A sales shutdown may eventually force wells offline.
Understanding the whole system makes troubleshooting much easier.
What Should a New Operator Learn First About a LACT Unit?
Start by physically tracing the oil.
Find the storage tank.
Find the pump suction.
Find the pump discharge.
Find the strainer.
Find the gas eliminator.
Find the quality measurement.
Find the flow meter.
Find the sampler.
Find the diverter valve.
Find the pipeline outlet.
Then learn the normal operating values.
What is normal suction pressure?
What is normal discharge pressure?
What is normal flow?
What is normal BS and W?
What is normal tank level?
What is normal temperature?
Once those values are familiar, abnormal conditions become much easier to recognize.
Why Is Trend Data Valuable?
One reading only tells you what is happening at one moment.
A trend shows how the process changed.
Suppose LACT flow has gradually decreased over several days while differential pressure across the strainer increased.
That points toward a restriction.
Suppose high BS and W occurs every morning when oil temperature is lowest.
That suggests temperature may be influencing separation.
Suppose the pump trips only when tank level becomes low.
Suction conditions may be involved.
Good troubleshooting looks for relationships.
Why Is the LACT Unit More Important Than It Looks?
A LACT skid may occupy only a small area of a large production facility.
But nearly every barrel of saleable oil may eventually pass through it.
The well can produce normally.
The separator can work.
The heater treater can work.
The tanks can contain good crude.
But if the custody transfer system cannot measure and move that crude, the producer cannot complete the sale.
That makes the LACT one of the most commercially important pieces of equipment at many oil production facilities.
Frequently Asked Questions
What does LACT stand for in oil and gas?
LACT stands for Lease Automatic Custody Transfer.
What is a LACT unit used for?
A LACT unit measures, samples, checks, and transfers crude oil when custody changes from a producer to a purchaser or receiving pipeline.
Does a LACT unit measure crude automatically?
Yes. Many LACT systems automatically measure flow, temperature, quality, and transferred volume while controlling the transfer process.
What is BS and W?
BS and W means basic sediment and water. It represents water and unwanted sediment contained in the crude stream.
Why does high BS and W stop a crude oil sale?
The purchaser does not normally want to pay crude oil value for excessive water and sediment. The LACT can divert the crude until it meets the required specification.
What does the LACT pump do?
The pump moves crude through the measurement equipment and provides enough pressure for the oil to enter the receiving pipeline.
Why does the LACT need a flow meter?
The meter determines how much liquid passes through the custody transfer point.
What is a meter factor?
A meter factor is a correction value that accounts for the actual measured performance of the custody transfer meter.
What does proving a LACT meter mean?
Proving means comparing the meter against a known reference volume to confirm its accuracy and determine the appropriate meter factor.
Why is temperature measured during crude transfer?
Crude changes volume as temperature changes. Temperature measurement allows the observed volume to be corrected to a standard reference condition.
What is a LACT sampler?
A LACT sampler collects small portions of crude throughout a transfer to create a representative composite sample for quality testing.
What happens when a LACT detects wet crude?
The system can divert the crude away from the sales pipeline and send it back to storage or treatment.
Why would a LACT unit trip on low suction pressure?
Possible causes include low tank level, a plugged strainer, restricted piping, closed valves, cold viscous crude, or gas entering the pump suction.
Why does a LACT pump cavitate?
Cavitation can occur when suction pressure becomes too low and vapor bubbles form inside the pump.
Can a LACT failure shut in producing wells?
Yes. If oil cannot be sold and the storage tanks become full, operators may eventually need to reduce or shut in production.
Is a LACT unit the same as a separator?
No. A separator separates production fluids. A LACT unit measures and transfers treated crude at the custody transfer point.
Is a LACT unit the same as a heater treater?
No. A heater treater helps remove water from crude. The LACT verifies and measures the treated oil when it is sold.
Can a bad BS and W sensor reject good oil?
Yes. Instrument problems can create incorrect readings, which is why unexpected measurements should be verified.
Why are storage tanks often located before the LACT?
The tanks provide inventory capacity and additional settling time while allowing production and sales to operate at different rates.
What should an operator check first when a LACT will not run?
Check tank level, valve lineup, active alarms, pump readiness, suction pressure, pipeline pressure, crude quality, and instrument status before assuming the control system has failed.
Why is LACT measurement financially important?
The measured quantity and quality determine how much crude oil is credited during custody transfer. Small repeated errors can become financially significant over large volumes.
What is the most important thing to understand about a LACT unit?
Understand the entire crude flow path from storage through the pump, conditioning equipment, quality measurement, meter, sampler, diverter valve, and sales pipeline. Once that path is clear, most LACT problems become much easier to troubleshoot.