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Flare and vent systems exist in essentially all segments of the oil and gas industry and are

used for two basic types of waste gas disposal: intermittent and continuous. Intermittent

applications may include the disposal of waste volumes from emergency pressure reliefepisodes, operator initiated or instrumented depressurization events (e.g.,

depressurization of process equipment for inspection or maintenance purposes, or

depressurization of piping for tieins!, plant or system upsets, well servicing and testing,pigging events, and routine blowdown of instruments, drip pots and scrubbers.

"ontinuous applications may include disposal of associated gas and#or tan$ vapours at oil

production facilities where gas conservation is uneconomical or until such economics canbe evaluated, casing gas at heavy oil wells, process waste or byproduct streams that either

have little or no value or are uneconomical to recover (e.g., vent gas from glycol

dehydrators, acid gas from gas sweetening units, and sometimes stabilizer overheads!,

and vent gas from gasoperated devices where natural gas is used as the supply medium(e.g., instrument control loops, chemical in%ection pumps, samplers, etc.!. &ypically,

waste gas volumes are flared if they pose an odour, health or safety concern, and

otherwise are vented.

&here are inconsistencies in what individual companies may include in their reported

vented and flared volumes and, depending on the %urisdiction, this information may notbe reported at all. &he vented and flared volumes reported in production accounting

statistics typically comprise, where applicable, casing gas venting, waste associated gas

flows, treater and stabilizer offgas and gas volumes discharged during process upsets andequipment depressurization events. 'torage and loading#unloading losses are assumed to be

generally excluded from reported vented volumes, and, therefore, are assessed separately.

iscellaneous vented and flared volumes not normally included in reported vented and

flared volumes may include instrument vent gas, compressor start gas, purge gas and blan$etgas that is discharged directly to the atmosphere, dehydrator still column offgas, purge gas

and releases from inspection and maintenance activities.

)here vented and flared volumes are reported all measured quantities are usually

captured* however, flow meters are normally only installed on larger continuous vent or

flare systems, if at all. )here there is no measurement data the volumes may still beestimated. &he problems here are the lac$ of detailed estimation guidelines, the lac$ of

any formal trac$ing of the activity data needed to ma$e many of these estimates (e.g.,

frequency and details of equipment or piping blowdown events, frequency of compressor

engine starts, etc!, and differences in which sources individual operators are evenconsidering.

+istorically, there has been a problem throughout the industry with some vented volumesbeing reported as flared. &he actual split has a significant impact on the total "-

equivalent ("2! emissions from these activities since unburned "+/contributes

approximately 0.0 times more radiative forcing on a 122year time horizon than fullycombusted "+/. ften production accounting forms for production facilities, the ma%or

source of venting and flaring, only provide a single cell for reporting of total vented and

flared volumes.

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3t gas processing plants, acid gas volumes are normally reported separately from other

venting or flaring volumes* however, the latter amounts are reported as a single

aggregated value. 4enting and flaring from gas gathering systems is also reported as asingle aggregate value.

'ome operators have tended to use vented and flared entries as balancing terms toachieve reasonable metering differences when completing production accounting reports.

&he problems with conserving or vented and flared volumes may include small volumesinvolved at individual sites, inconsistencies in flow, poor access to gas gathering systems,

concerns about putting any bac$pressure on the casing in order to use the gas, and

operational difficulties associated with using this gas (e.g., freezeup problems in the

winter! in the absence of any costly onsite dehydration facilities.

&he actual quantification of flows in a flare system allows a review of the economics

associated with conserving the flare gas. &he amount of residual flow in intermittent flare

systems is the sum of the purge gas flow rate and lea$age rates into the flare system. &odistinguish between purge gas flows and lea$age, the minimum required purge gas rate

may be calculated using the procedure presented by 'tone et al. (155-!, and subtractedfrom the total residual flare rate. &he difference is then the amount of lea$age or

potentially avoidable gas loss.

6hysical 3coustics "orporation has developed an acoustic lea$ detector, which

incorporates a lea$ quantification algorithm developed by 7ritish 6etroleum, for

detecting and quantifying lea$age through flare and steam valves. &he technology has

proven very useful in both identifying which valves are lea$ing into flare and ventheaders, and facilitating ob%ective repair decisions. 6anametrics Inc. has developed a

clampon ultrasonic flow meter that may be used to measure gas flows through lea$ing

valves* their instrument offers better accuracies but requires more effort to use and hassome limitations regarding the minimum allowable gas pressure in the pipe. ther

methods include velocity measurements and tracer tests.

In each case, the hydrocarbon concentration in the stream should be determined using aportable combustiblegas detector or based on a detailed laboratory analysis of the flare

gas (where available!.

&otal residual gas flows in the flare systems at / older gasprocessing plants in the 8'(i.e., flows outside of blowdown or emergency relief events! amounted to -.90 x 12 9

m9#d#site (2.22-- t "-#y#site! or -/./ percent of total natural gas losses at each site.

'imilar results have been observed at gas processing plants in "anada. In several casesthe flows from individual systems were sufficient to potentially %ustify installing a flare

gas recovery unit. 3nother option is to target the actual source or sources of the residual

gas flow in these systems (e.g., excessive purge gas consumption and lea$ing pressure

relief devices, drains and blowdown valves connected to the flare header!. &ypically,these causes are difficult to isolate, usually require a ma%or plant shutdown to fix and are

li$ely to reoccur.