Modelling offshore emissions from oil and gas platforms

Modelling offshore emissions from oil and gas platforms Ralph Burton, Stéphane Bauguitte, Ioana Colfescu, James Lee, Stephen Mobbs (PI), Ruth Purvis, Axel Wellpott, Shona Wilde, Stuart FAAM staff

Emission estimates: methods used Gaussian method Mass flux method • Established method • Easy to implement • Baseline removal: 1 D • Baseline removal: 2 D • Requires background wind to be greater than ~4 -5 m/s • Requires plumes to be of Gaussian shape WRF-LES (Large Eddy Simulation) • Full atmos-pheric model • Need knowledge of WRF, plus access to parallel processing machine • Needs an estimate of release rate • - but can have varying release rate Ideally, use all three methods

I. MASS FLUX METHOD MARCH 2019 Example of reconstructed methane plume (using Barnes interpolation).

I. MASS FLUX METHOD The method can also be applied to other gases. Methane Ethane

II. GAUSSIAN METHOD

II. GAUSSIAN METHOD

II. GAUSSIAN METHOD Example of plume characteristics σy is related to the lateral spread of the plume Peak concentrations (above background) Gaussian fit to observations

II. GAUSSIAN METHOD Elgin uncontrolled release, 2012

III. WRF-LES METHOD Weather Research and Forecasting (WRF) simulations • • • State-of-the-art weather forecasting model. Can be used at scales of 10 s of km to 10 s of m 40, 000 users in 160 countries Sophisticated representations of turbulence, microphysics, radiation, etc. Has been adapted by NCAS for use with release of gas Gives a three-dimensional simulation of plume evolution.

height (m) III. WRF-LES METHOD Initialise with vertical profile obtained from the aircraft (temperature, winds. ) MARCH 2019 θ (K) Use a feasible value (derived from either Gaussian method or mass-flux) for release rate. Process results. Do they agree with observations?

III. WRF-LES METHOD MARCH 2019 Distribution of gas in the vertical Simulation of plume transect at 300 m ASL

WRF modelling of BP drone flight – preliminary results BP drone observed extended area of methane on route to Clair. Was Clair Ridge the source of methane? Courtesy Dan Touzel / BP / WRF modelling with Clair Ridge as source

10 m 100 m 30 m GFS analyses valid 06 Z

WRF modelling with Clair Ridge as source

WRF methane (PPM) ASL 100 m

Clair Ridge Clair best guess at drone flight track WRF methane (PPM) 08 Z 100 m ASL ;

BP drone Dan Touzel / BP WRF on same domain (best estimate)

WRF methane interpolated to 100 m ASL, along best guess of flight track, valid at 08 Z Dan Touzel / BP N S South North

streamlines, 100 m ASL, 09 Z streamlines, 300 m ASL, 09 Z

Summary • WRF results are consistent with BP findings that extended methane area could have originated in Clair Ridge • Would need geo-located measurements of methane to do a more rigorous comparison with WRF …would need (bare minimum): lat, lon, altitude, CH 4, time