Where does the oxygen at custody transfer come from?
It is air drawn in at the surface, not from the reservoir.
Produced natural gas leaves the reservoir essentially oxygen-free, so every part-per-million of O₂ measured at custody transfer is air pulled in somewhere upstream. It enters at the wellhead (sub-atmospheric pressure on declining and stripper wells, plunger-lift and unloading venting), at tanks and vapor-recovery units (thief hatches and VRU equipment), at compressor stations (worn rod packing on sub-atmospheric suction), and across gathering (fittings, valve packing, dresser couplings, and porous welds). None of these sources is large on its own — but they accumulate, and the converged stream arrives at the custody point carrying the sum.
What is the oxygen limit for custody transfer?
Pipeline tariffs publish a maximum O₂ — commonly around 10 ppm.
At custody transfer the pipeline takes ownership of the gas and measures it for quality and quantity. Gas-quality specifications, including a maximum oxygen content, are written into each pipeline's tariff and gas sales agreement; interstate systems commonly enforce a limit on the order of ~10 ppm, though the exact figure varies by pipeline and contract. [Confirm the specific O₂ spec for your target interconnect.] When delivered gas is above the published limit, the pipeline can refuse to accept it, apply a penalty, or require the seller to remediate or blend it back into spec.
What happens when gas is off-spec on oxygen at the meter?
The seller carries the cost — rejection, penalty, or shut-in.
Because quality is measured at the custody point, an off-spec oxygen reading lands on the producer's side of the meter. Consequences range from rejection of the gas and contractual penalties to forced shut-in, reprocessing, or contractual blending with compliant gas to stay in spec — all of which cost real revenue and operating time. Oxygen is also one of the more corrosive contaminants in wet gas: combined with water and CO₂/H₂S it accelerates internal corrosion and microbiologically influenced corrosion (MIC), so an O₂ problem at the fence line is often an asset-integrity problem in the miles of line behind it.
How does OxyScout protect custody transfer?
Continuous optical O₂, measured before the bill comes due.
OxyScout reads oxygen continuously at or just upstream of the custody-transfer point using luminescence-quenching optical sensing — so cumulative ingress is caught before it crosses the tariff line, and it can drive alarms and divert or shut-in logic before off-spec gas reaches the sales meter. Pair it with checkpoints at the wellhead, tanks, compressor, and gathering taps and a high reading at custody transfer can be localized back to the offending stage instead of leaving you to hunt the whole field. Because the measurement is optical, there is no galvanic cell to deplete and replace on a schedule, which means less drift, fewer truck rolls, and a lower total cost of ownership than legacy electrochemical analyzers.
Benefits of OxyScout for Custody Transfer
Measures the gas you sell — Reads O₂ at or just before the custody point, where the tariff is actually enforced.
Catches cumulative ingress — Sums four upstream sources into one defensible custody-point reading.
No consumable cell — Optical sensing; nothing to deplete or replace on a schedule.
Drift-resistant & fast — Holds calibration and responds quickly as oxygen rises or falls.
Localizes the source — Pair with wellhead, tank, compressor and gathering taps to find the offending stage.
Protects revenue — Alarm and divert before off-spec gas hits the sales meter — avoid rejection and penalties.
Guards asset integrity — Early O₂ detection limits internal corrosion and MIC across wet lines.
Lower 2–3 yr TCO — No cell swaps and fewer truck rolls put total cost below legacy electrochemical.