Tank Battery

A tank battery is a group of surface storage tanks that receives crude oil production from one or more wells on a producing lease. The tanks hold the produced oil after it has been separated from gas and water, before the oil is shipped out by truck or pipeline. A typical tank battery has two or more oil tanks for receiving production, one or more saltwater tanks for produced water, and ancillary equipment for emergency containment, vapour recovery, and metering. Tank batteries are everywhere in onshore oil production. Most lease pumpers spend their daily routes driving from one tank battery to the next, gauging fluid levels, checking for leaks, and recording production. The hardware looks simple, but the reliable operation of a small tank battery is the practical foundation on which every onshore oil revenue stream depends.

Key Takeaways

A tank battery is a group of surface storage tanks at a producing lease, used to receive crude oil from one or more wells. The battery sits at the end of the gathering system after separators have removed gas and water from the produced fluid stream.
The tanks themselves are typically welded steel cylinders 4 to 8 metres in diameter and 6 to 9 metres tall, holding 250 to 1,000 barrels each. A small lease might have a battery of 2 to 4 tanks. A larger field facility might have 8 to 20 tanks plus dedicated produced-water storage.
Tanks are connected by a manifold that lets oil flow from any inlet to any tank, and from any tank to the truck loadout or pipeline outlet. The manifold gives the operator flexibility to switch tanks for filling, settling, sampling, and shipping without interrupting well production.
Modern tank batteries include vapour recovery systems that capture light hydrocarbons evaporating from the tank tops, instead of venting them to atmosphere. The recovered vapours are piped back into the gas sales line. Vapour recovery is required by environmental regulations in most North American producing regions and reduces methane emissions significantly.
Secondary containment surrounds the battery: an earthen berm or concrete dike sized to hold 110 to 150 percent of the largest tank's volume, in case of a tank rupture or overfill. The containment prevents spilled oil from migrating off the lease and is required by federal and provincial spill prevention rules.

Fast Facts

The term "tank battery" comes from the artillery use of "battery" to mean a grouped set of similar units (an artillery battery is a group of cannons; a tank battery is a group of tanks). The word entered oilfield use in the 1880s in the Pennsylvania oil fields and has stayed in continuous use ever since. The earliest tank batteries were wooden tanks that leaked steadily; by the 1920s, riveted steel tanks had become standard; by the 1940s, welded steel construction took over and remains standard today. The basic engineering is over a century old, but the regulations around vapour recovery, containment, leak detection, and metering have evolved continuously and now drive most of the design complexity of modern installations.

What Happens at a Tank Battery

Picture a small fenced compound off a county road in west Texas or central Saskatchewan. Inside the fence: half a dozen large white-painted steel tanks, a few smaller separator vessels, a stand of pipework with valves and gauges, a flare stack, and a truck loading platform. The wellhead and pump jack of the producing well are usually a few hundred metres away, connected to the tank battery by a buried flow line. This is a typical small-lease tank battery, and there are tens of thousands of them across North America.

Produced fluid arrives from the wellhead through the flow line, enters the separator (a horizontal or vertical vessel that uses gravity and pressure drop to split the stream into gas, oil, and water), and the separated oil flows into the manifold. The manifold directs the oil to a tank, where it sits while any remaining water and sediment settle to the bottom. Settled water is drained off the tank bottom into the saltwater tanks, leaving clean oil ready for sale.

When a tank fills, the operator switches the inlet manifold to direct flow to the next available tank, isolates the full tank for sampling and gauging, and schedules a truck or pipeline shipment. A trucking company sends a tanker, which connects to the loadout valve, draws the oil out of the tank, hauls it to a midstream gathering point or refinery, and the cycle repeats. On larger leases, oil flows out through a pipeline rather than trucks, but the same basic flow logic applies.

Where Tank Batteries Sit in the Oil Production System

Every onshore oil well that produces commercial volumes has a tank battery somewhere downstream. A tank battery serves one well in the simplest case (a single producing well with a dedicated battery on the same lease) or many wells in larger fields (a centralized battery receiving production from a dozen or more wells gathered through a network of flow lines). The battery is the boundary between the production system (everything from the reservoir to the tank inlet) and the marketing system (everything from the tank outlet to the refinery).

The tank battery is also where production accounting starts. Tank gauging produces the inventory numbers that get reported to the operator's accounting system, the royalty owners, and the regulator. The Texas Railroad Commission, the Alberta Energy Regulator, the Saskatchewan Ministry of Energy and Resources, and equivalent bodies in every producing jurisdiction require regular tank gauging reports as part of their production reporting framework. Errors in tank gauging propagate directly into royalty calculations and tax liability, so the gauging procedure is taken seriously.

Lease pumpers (the field workers who manage producing wells) spend most of their day on the road between tank batteries. A typical pumper covers 20 to 60 tank batteries on a daily route, gauging tank levels, checking for leaks, restarting any wells that have shut down on alarm, and writing up the daily production report. The work is unglamorous and absolutely essential. The reliable operation of the tank battery is what converts the well's underground production into recognized revenue at surface.

A tank battery is also called a tank farm (more common for larger facilities), an oil battery, or just "the battery" in field shorthand. The smaller version on a single-well lease is sometimes called a single-well battery or a stock tank battery. Related terms include separator (a pressure vessel that splits the produced fluid stream into gas, oil, and water phases by gravity and pressure drop; sits upstream of the tank battery and feeds it with separated oil), lease pumper (the field worker responsible for the day-to-day operation of producing wells and tank batteries on a lease; gauges tanks, monitors equipment, and reports production), vapor recovery (a system that captures light hydrocarbon vapours from tank tops and returns them to the gas sales line instead of venting them to atmosphere; required by environmental regulations in most North American producing regions), secondary containment (an earthen berm or concrete dike around a tank battery sized to hold the volume of the largest tank, plus margin; prevents spilled oil from migrating off the lease and is required under federal and provincial spill prevention rules), and LACT unit (Lease Automatic Custody Transfer, the metering and quality-measurement system used to transfer custody of crude oil from the tank battery to a pipeline buyer; replaces manual gauging on automated pipeline-connected batteries).

Why a Routine Tank-Gauging Visit Catches a Six-Figure Mistake

A lease pumper on a Saskatchewan route arrives at Tank Battery 11 on his morning rounds. He has gauged this battery five days a week for two years. The morning routine is: open the thief hatch on each tank, drop a calibrated steel tape and bob to the oil surface, read the level, write it down, close the hatch, move to the next tank.

This morning, Tank 3 reads 14.2 feet of oil. Yesterday it read 13.8 feet. The well feeding the battery was producing 80 barrels per day on the latest test. Four-tenths of a foot in this size of tank is about 6.8 barrels of oil. The well should have added closer to 80 barrels in the past 24 hours, plus or minus a few barrels for any water cut variation.

The pumper walks the battery. He finds a small wet spot in the dirt under the saltwater tank manifold, a leak that has been weeping for at least 12 hours. The leak is on a fitting that is supposed to connect the saltwater drain line to the disposal pipe. Instead of draining water, it has been diverting oil-water mix from the tank into the dirt at the base of the battery. He shuts in the leak, starts a spill response protocol, and calls the production foreman.

The cleanup costs CAD 14,000. The reportable spill is small enough that the regulator accepts the voluntary disclosure without a fine. If the pumper had skipped the daily gauge for another two days (a "good enough" temptation when nothing seems wrong), the leak could have grown into a CAD 80,000 to CAD 250,000 cleanup with regulatory penalties. The math is simple. Tank gauging is a 12-minute task per battery. Across 28 batteries on a route, the daily gauge is the difference between catching small problems early and managing large problems later. The tank battery is the smallest and most fundamental piece of oilfield surface infrastructure, and the daily routine of looking after it is one of the most economically valuable practices in the industry.