Methods
Estimation model
Twelve sources, each with the equation family that produces it, the tier that classification implies and the measurement that would raise it. Rendered from the running engine, so this page cannot describe a method the code has moved away from.
The twelve sources
| Source | Family | Equation family | Tier | Route to a higher tier |
|---|---|---|---|---|
Flare — uncombusted methane | Combustion slip | flare-combustion split | Tier 2 | Direct measurement of flare combustion efficiency |
Crude-tank flashing | Flashing & venting | Vasquez-Beggs solution gas | Tier 3 | — |
Produced-water degassing | Flashing & venting | Henry's law | Tier 3 | — |
Shuttle-tanker loading | Flashing & venting | loading factor | Tier 2 | Vapour measurement during a loading operation |
Compressor rod-packing vents | Equipment loss | gas-duty scaled | Tier 1 | Vent-rate measurement or component count |
Compressor wet-seal vents | Equipment loss | gas-duty scaled | Tier 1 | Seal-type confirmation and vent measurement |
TEG reboiler vent | Equipment loss | gas-duty scaled | Tier 1 | Still-column vent measurement |
Equipment fugitives | Equipment loss | time-in-service scaled | Tier 1 | Component count and leak-detection survey |
Pneumatic devices | Equipment loss | time-in-service scaled | Tier 1 | Device inventory and drive-medium survey |
Cold vents / blowdowns | Equipment loss | time-in-service scaled | Tier 1 | Blowdown event log |
Sand handling | Equipment loss | time-in-service scaled | Tier 1 | — |
MEG-regeneration flash vent | Flashing & venting | confirmed zero base | Tier 3 | — |
Every uncertain parameter
These are what the Monte-Carlo ensemble samples. The distribution shape is not a detail: over the same bounds, a triangular and a PERT on flare combustion efficiency differ by 17% in the mean slip, on a term carrying about 70% of national methane.
| Parameter | Distribution | Range | Provenance | Shape |
|---|---|---|---|---|
| eta_cFlare combustion efficiency — the fraction of flared methane destroyed | pert | 0.94 – 0.98 – 0.995 | assumed with range | Bounded and concentrated near the mode: the mode is where the evidence points and the bounds are what cannot be excluded. |
| flash_ch4Methane fraction of crude-tank flash gas | triangular | 0.15 – 0.274 – 0.4 | assumed with range | Bounded, with weight falling linearly to each bound. More tail weight than a PERT over the same bounds. |
| P_lpLow-pressure separator pressure, psia | triangular | 25 – 50 – 90 | assumed with range | Bounded, with weight falling linearly to each bound. More tail weight than a PERT over the same bounds. |
| pw_ventFraction of produced-water dissolved gas that reaches atmosphere | triangular | 0.3 – 0.7 – 1 | assumed with range | Bounded, with weight falling linearly to each bound. More tail weight than a PERT over the same bounds. |
| pw_multMultiplier on the produced-water degassing estimate | triangular | 0.4 – 1 – 1.6 | assumed with range | Bounded, with weight falling linearly to each bound. More tail weight than a PERT over the same bounds. |
| act_multMetering uncertainty on reported Petroleum Commission volumes | lognormal | ×÷ 1.03 at 95% | assumed with range | Multiplicative. A factor of 2 means the value could plausibly be twice or half the base rate, which is how an emission-factor uncertainty is normally stated. |
| m_rpUncertainty multiplier — compressor rod-packing vents | lognormal | ×÷ 2 at 95% | assumed with range | Multiplicative. A factor of 2 means the value could plausibly be twice or half the base rate, which is how an emission-factor uncertainty is normally stated. |
| m_wsUncertainty multiplier — compressor wet-seal vents | lognormal | ×÷ 2.5 at 95% | assumed with range | Multiplicative. A factor of 2 means the value could plausibly be twice or half the base rate, which is how an emission-factor uncertainty is normally stated. |
| m_tegUncertainty multiplier — TEG reboiler vent | lognormal | ×÷ 1.65 at 95% | assumed with range | Multiplicative. A factor of 2 means the value could plausibly be twice or half the base rate, which is how an emission-factor uncertainty is normally stated. |
| m_aefUncertainty multiplier — equipment fugitives | lognormal | ×÷ 2 at 95% | assumed with range | Multiplicative. A factor of 2 means the value could plausibly be twice or half the base rate, which is how an emission-factor uncertainty is normally stated. |
| m_pneuUncertainty multiplier — pneumatic devices | lognormal | ×÷ 1.5 at 95% | assumed with range | Multiplicative. A factor of 2 means the value could plausibly be twice or half the base rate, which is how an emission-factor uncertainty is normally stated. |
| m_cvUncertainty multiplier — cold vents and blowdowns | lognormal | ×÷ 1.8 at 95% | assumed with range | Multiplicative. A factor of 2 means the value could plausibly be twice or half the base rate, which is how an emission-factor uncertainty is normally stated. |
| m_sandUncertainty multiplier — sand handling | lognormal | ×÷ 2.5 at 95% | assumed with range | Multiplicative. A factor of 2 means the value could plausibly be twice or half the base rate, which is how an emission-factor uncertainty is normally stated. |