Johnson2011-An Analysis of Flaring and Venting Activity in the Alberta Upstream Oil and Gas Industry

An Analysis of Flaring and Venting Activity in the AlbertaUpstream Oil and Gas Industry

Matthew R. Johnson and Adam R. CoderreMechanical and Aerospace Engineering, Carleton University, Ottawa, Ontario, Canada

ABSTRACTAlberta, Canada, is an important global producer of pe-troleum resources. In association with this production,large amounts of gas (1.14 billion m3 in 2008) are flared orvented. Although the amount of flaring and venting hasbeen measurably reduced since 2002, data from 2005reveal sharp increases in venting, which have importantimplications in terms of resource conservation and green-house gas emissions (which exceeded 8 million tonnes ofcarbon dioxide equivalent in 2008). With use of extensivemonthly production data for 18,203 active batteries span-ning the years 2002–2008 obtained in close cooperationwith the Alberta Energy Resources Conservation Board, adetailed analysis has been completed to examine activitypatterns of flaring and venting and reasons behind thesetrends in the Alberta upstream oil and gas industry. In anygiven year, �6000 batteries reported flaring and/or vent-ing, but the distribution of volumes flared and vented atindividual sites was highly skewed, such that small num-bers of sites handled large fractions of the total gas flaringand venting in the Province. Examination of month-to-month volume variability at individual sites, cast in termsof a nominal turndown ratio that would be required for acompressor to capture that gas and direct it into a pipe-line, further revealed that volumes at a majority of siteswere reasonably stable and there was no evidence thatlarger or more stable sites had been preferentially reduced,leaving potential barriers to future mitigation. Throughlinking of geospatial data with production data coupledwith additional statistical analysis, the 31.2% increase in

venting volumes since 2005 was revealed to be predomi-nantly associated with increased production of heavieroils and bitumen in the Lloydminster region of the Prov-ince. Overall, the data suggest that quite significant re-ductions in flaring and venting could be realized by seek-ing mitigation solutions for only the largest batteries inthe Province.

INTRODUCTIONIn the energy and petrochemical sectors, it is commonpractice to dispose of surplus flammable gases by flaring(i.e., combustion in an open-atmosphere flame) or vent-ing (i.e., release of gases directly to the atmosphere). TheU.S. Energy Information Administration estimates that95.6 billion m3 of gas were flared or vented worldwide in2005.1 Analysis of satellite imagery using visible lightcamera data suggests that global flaring rates alone mayexceed 139 billion m3 annually.2 Even with the assump-tion of 100% carbon conversion efficiency, greenhousegas (GHG) emissions from this latter amount of flaringwould equate to 289 million tonnes of carbon dioxide(CO2) annually. To the authors’ knowledge, reliableglobal data for venting volumes do not exist. However,because the major component of most flared and ventedgas is methane (a potent GHG with a global warmingpotential 25 times greater than that of CO2 on a massbasis3), GHG emissions associated with even relativelysmall volumes of vented gas can also be quite significant.

Flaring in the petroleum industry generally fallswithin three broad categories: emergency flaring (large,unplanned, and very short-duration releases, typically atlarger downstream facilities or off-shore platforms), pro-cess flaring (intermittent large or small releases that maylast for a few hours or a few days, as occurs in the up-stream industry during well-test flaring to assess the sizeof a reservoir or at a downstream plant during a plannedprocess blowdown), and production flaring (which mayoccur continuously for years as the resource, oil, is beingproduced).4,5 Venting may also occur in various sectors ofthe industry including at downstream gas plants and ingas transmission pipelines, but the vast majority of vent-ing occurs at upstream production sites and at heavy oilwells in particular. Whereas overall volumes of vented gasare generally quite significant, individual sources are usu-ally smaller.

Pollutant emissions associated with oil and gas pro-duction have been the subject of a number of recentstudies6–12 and over the past decade, there has been a

IMPLICATIONSGlobal flaring and venting of substantial volumes of wasteflammable gases is a significant environmental concern.Alberta, Canada, is an example of a jurisdiction that hasachieved significant reductions in flare and vent volumesfrom historic highs; however, these efforts have stalled inrecent years. Through unprecedented access to severalyears of site-by-site production data for the entire upstreamoil and gas industry in this region, a detailed analysis ofcurrent practices and activity trends in flaring and venting inAlberta has been made possible for the first time. Theresults of this analysis, including a specific investigation ofpotential barriers to mitigation of flaring and venting in amature oil- and gas-producing region, have important im-plications for flaring and venting mitigation throughout theworld.

TECHNICAL PAPER ISSN:1047-3289 J. Air & Waste Manage. Assoc. 61:190–200DOI:10.3155/1047-3289.61.2.190Copyright 2011 Air & Waste Management Association

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concerted global effort to reduce volumes of gas beingflared and vented,13 in large part because of concernsabout emission of GHGs and pollutants such as particu-late matter and sulfur dioxide, but also because flaringand venting destroy a potentially valuable resource.14–18

However, the scale of the problem is enormous and thecomplexities of the oil and gas industry, coupled with thediversity of situations under which flaring and venting areapplied, preclude single solutions. Moreover, in the ma-jority of situations in which flaring or venting occurs ona continuous basis, the raw gas has little to no localeconomic value. This may be due to a combination offactors such as an absence of infrastructure necessary tocollect and transport the gas, challenges related to un-steady or intermittent flow, low gas heating value, thepresence of H2S or other contaminants, or the absence ofa local market to consume the gas.

Although progress in reducing flaring and ventingglobally has been somewhat limited, certain jurisdictionshave achieved varying degrees of success. One of these isthe Province of Alberta, Canada, which had a reduction inflared and vented volumes of 51% between 1999 and2008.19 The purpose of this paper was to analyze opera-tional data for the Alberta Upstream Oil and Gas sectorobtained in partnership with the Alberta Energy Re-sources Conservation Board (ERCB) to examine recenttrends in flaring and venting activity within the Province,to investigate potential reasons for the observed trends,and to determine what these trends suggest about poten-tial opportunities and barriers to further mitigation.

Flaring and Venting in Alberta, CanadaThe province of Alberta, Canada, is one of the largestpetroleum-producing regions in North America. In 2008,there were more than 175,000 active oil and gas wells inthe province, which produced 184 million barrels of con-ventional crude oil, 133 billion m3 of salable gas, and 214million barrels of “crude bitumen.” The ERCB definescrude bitumen as being either heavy oil (“crude oil havinga density of 920 kg/m3 or greater at 15 °C”) or crudebitumen (“a naturally occurring viscous mixture, mainlyof hydrocarbons heavier than pentane, that may containsulfur compounds and that in its naturally occurring vis-cous state will not flow to a well”).20 This category ex-cludes mined oil sands. In practice, the labels “oil battery”or “bitumen battery” are inconsistently applied; however,this is not critical because these batteries are considered inaggregate for most of the present analysis.21 A further 264million barrels of oil equivalent were produced throughmining and processing of oil sands. Flaring and ventingfrom all reported sources in the upstream oil and gasindustry in Alberta totaled 1.14 billion m3 of gas in 2008.By assuming a typical composition for this gas including86% methane and an ideal 100% carbon conversion effi-ciency for flares, this equates to at least 8.03 milliontonnes of CO2 equivalent greenhouse gas emissions an-nually. Environment Canada estimates that flaring andventing represent as much as 25.5% of total GHG emis-sions associated with upstream oil and gas production inCanada (29.5% excluding oil sands production).22

Most conventional oil production in Alberta origi-nates from smaller volume wells that are directed to facil-ities known as “batteries,” where primary separation ofoil, water, and solution gas (also known as associated gas)takes place. The term “solution gas” is generally used todescribe any dissolved gases that come out of solutionwhen reservoir liquids are reduced from reservoir to at-mospheric pressure. Gases that are separated out at abattery can be flared, vented, or conserved (i.e., collectedand used for on-site fuel or directed into pipelines forfurther refining and sale). There are nearly 20 thousandoil and bitumen batteries in Alberta, which produced 14.8billion m3 of solution gas in 2008. Although the largemajority of solution gas in Alberta is typically conserved(95.1% in 2008), the remaining fraction represents a sig-nificant volume of gas (723 million m3 in 2008).19

As shown in Figure 1, the majority of flaring andventing in Alberta’s upstream oil and gas industry occursat crude oil and crude bitumen (in this context crudebitumen is believed to be predominantly heavy oil) bat-teries, which accounted for 34 and 29% of total volumesin 2008. Moreover, 92% of all venting in the upstream oiland gas industry is attributable to these same batteries.19

Because the major component of solution gas is methane,GHG emissions associated with this level of venting makeoil and bitumen batteries an important target for mitiga-tion measures. Over the past decade, there has been con-siderable effort to reduce the volumes of gas being flaredand vented at oil and bitumen batteries in Albertathrough measures such as the introduction of operationalregulations in ERCB Directive 60 (D60).23 Nevertheless,the volumes of gas still being flared and vented are signif-icant, and, as discussed below, although volumes of flaredgas have shown a steady decline, volumes of vented gashave been increasing in recent years. In this paper, pro-duction data from more than 18,000 oil and bitumen

Figure 1. Breakdown of flaring and venting volumes by sector ofthe upstream oil and gas industry in Alberta in 2008.19 CBM, coal bedmethane.

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batteries in Alberta were analyzed to elucidate a range ofrecent trends and examine reasons for these develop-ments. In addition, changes in venting and implicationsof operational data on future opportunities and barriers tofurther mitigation are specifically explored.

METHODOLOGYMonthly production data from 18,203 oil and bitumenbatteries in the Province of Alberta, spanning the years2002–2008, were obtained in collaboration with theERCB. The ERCB is responsible for regulation of the up-stream oil and gas industry in Alberta, and guidelines forsolution gas flaring and venting are administered throughERCB D60.23 This directive requires that “[o]perators ofoil, bitumen, and natural gas production and processingfacilities (including well tests) must report volumes of gasgreater than or equal to 0.1 � 103 m3/month (adjusted to101.325 kPa(a) and 15 °C) that is flared, incinerated, orvented” through the Petroleum Registry of Alberta, alongwith their regular monthly production reports. The datapresented herein were derived from these industry-supplied reports. Although a subset of these data is madeavailable to the public, any data that are connected towells classified as experimental are withheld from publi-cation.24 Omission of these data is considered necessarybecause of the economically sensitive nature of experi-mental wells. The data presented in this paper are com-plete; however, proprietary data were protected by obscur-ing actual battery locations and operators.

In addition to constraints of confidentiality, dataanalysis was complicated by aggregate reporting. Al-though the majority of well sites are physically tied to thebatteries that report to the ERCB, this is not always thecase. Collections of individual wells that are not physi-cally connected can sometimes be reported as a singleentity; these are given battery codes for the purpose ofreporting, giving rise to the term “paper battery” becausethey only exist on paper. Of the 18,203 batteries con-tained in the data set, 296 were paper batteries. However,only 268 of these flared or vented gas between 2002 and2008, and only 213 flared or vented gas in 2008. It isgenerally assumed that wells in a paper battery are in thesame geographic area (i.e., within a few kilometers), al-though this is also not necessarily true. Thus, flare andvent volumes reported at a paper battery may actually bespread among multiple separate sites with separate flaresand/or vents. Actual locations of the individual wells areconsidered confidential; the influence of paper batteries

on this analysis and on publicly available data is con-sidered and discussed throughout the analysis pre-sented below.

The 84 monthly data reports, each containing8000–10,000 thousand entries, were imported into arelational structured query language (SQL) database foranalysis. The use of an SQL database enabled efficientcomputation of scripted queries involving iterative sta-tistical calculations even with these very large data sets.In this manner, monthly production and flare ventvolume data could be linked for all months between2002 and 2008, and these data could further be relatedto geographic location for nonconfidential batteries. Allscripted operations were validated by manually per-forming query-based calculations on selected cases toensure accuracy.

RESULTS AND DISCUSSIONData Overview

Between January 2002 and December 2008, 18,203 differ-ent oil and bitumen batteries reported production data,although only a fraction of that number reported in anygiven year. The year 2008 had the largest number of activeoil and bitumen batteries with 11,028, which produced atotal of 63.6 million m3 of oil and 14.8 billion m3 of gas.The bulk of this produced gas was conserved, although�4.9% of the gas was flared or vented. As summarized inTable 1, of 11,028 active batteries, 5945 reported flaringand/or venting activity in 2008, with 2360 facilities re-porting a total of 305.2 million m3 of flared gas and 4263facilities reporting 381.9 million m3 of vented gas. Ofthese, only 19 batteries (0.34%) were omitted from thepublished data24; however, these batteries accounted for6.3 million m3 (�2.1%) of all gas flared and 10.8 millionm3 (2.8%) of all gas vented. In total, 17.1 million m3 ofgas, representing 2.5% of the total for the Province, wereflared or vented from these batteries. Thus, although only0.32% of battery sites were omitted from 2008 publisheddata, their contribution to the total volumes being flaredand vented is nonnegligible.

In addition, 268 sites that reported flaring or ventingactivity between 2002 and 2008 were classed as paperbatteries, with 213 of these reporting activity in 2008(3.6% of all flaring or venting batteries). Although theseaccounted for only a small fraction (0.5%) of the totalvolume of flared gas, they were responsible for more than

Table 1. Overview of flaring and venting of solution gas at oil and bitumen batteries in Alberta in 2008a

Battery Type

Gas Flaring Gas Venting Combined Flaring and Venting

No. of Batteriesin 2008

Annual GasVolume (103 m3)





Unpublished 11 (0.5) 6263.8 (2.1) 12 (0.3) 10,801.6 (2.8) 19 (0.3) 17,065.4 (2.5)Paper 3 (0.1) 1648.4 (0.5) 213 (5.0) 136,560.2 (35.7) 213 (3.6) 138,208.6 (20.1)Standard 2347 (99.4) 297,826.2 (97.6) 4045 (94.9) 241,731.7 (63.3) 5720 (96.2) 539,557.9 (78.5)All 2360 305,179.2 4263 381,916.2 5945 687,095.4b

Notes: aVolumes are given in 103 m3 (percentage); bNote that the totals presented in this table differ from those originally presented in the ERCB ST60B report,which incorrectly included venting of combustion products.19

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one-third (35.7%) of all gas vented and more than one-fifth (20.1%) of total flare and vent volumes. Thus,although paper batteries are not a significant concernin the analysis of battery statistics for flared volumes,they are an important complication in the analysis ofventing activity.

Implied from the data shown in Table 1 is that ap-proximately half of the batteries producing in 2008 re-ported no flaring or venting, as they were presumably alltied into the pipeline network, used all produced solutiongas for on-site fuel, and/or flared and vented at levelsbelow the threshold reporting requirement of 0.1 � 103

m3/month. For the sake of obtaining an upper-limit esti-mate, even if each of these batteries was assumed to beflaring or venting the threshold limit amount, this wouldonly add 0.89% (6.1 million m3) to the reported annualtotal for oil and bitumen batteries.

Figure 2 shows trends in monthly volumes of gasflared and vented from 2002 to 2008 at oil and bitumenbatteries in Alberta. The symbols indicate magnitudes ofreported volumes, and the solid lines indicate the per-centages of the total gas volume that were flared or ventedeach month. As highlighted in ERCB’s ST60B report, thetotal quantities of gas flared and vented declined until2005, at which point the reductions essentially leveledoff, and total volumes increased slightly through 2008.19

A similar trend occurred in the vent volume data alone,although venting activity increased more dramaticallyfrom its minimum in 2005. Flared volumes, on the otherhand, have shown a steady decline since 2002.

The decision on whether to conserve or flare/vent thegas is part of the management framework set out in ERCBD60. In Alberta, oil and bitumen batteries disposing ofmore than 900 m3/day are required to perform an annualeconomic evaluation for conservation, and implementa-tion is required for such sites where conservation is eco-nomic (defined as having a calculated net present value ofgreater than �$50,000 Canadian dollars). In addition,existing sites of such size within 500 m of a residence are

required to conserve, regardless of economics. Existingsites of any size with gas/oil ratios (GORs) of more than3000 m3/m3 are also required to conserve. These ruleswere first implemented in 2000 and are thought to be afactor in the initial declining trends in total volumes ofsolution gas being flared and/or vented evident in Fig-ure 2. However, despite these measures, approximatelyhalf of the actual volume of flared or vented gas in 2008was from sites disposing of more than 900 m3/day,indicating that these sites were probably deemed un-economic to conserve.

Several observations can be made through analysis ofthe trends shown in Figure 2. Although overall reductionsin total annual volumes being flared and/or vented of34% were achieved from 2002 to 2005, data since 2005suggest that this trend has stopped. Moreover, consider-ing the steady increase in venting since 2005, it is appar-ent that venting accounts for an increasing proportionof the total gas volumes, or, put another way, the ratio offlaring to venting is decreasing. There are a number offactors that could be affecting these trends includingchanges in activity levels across the industry as new wellsare activated and older wells are retired, net changes inthe locations where the majority of solution gas is beingproduced within the Province, changes in typical volumesof gas being handled at individual batteries, increasedvariability of gas volumes at batteries as steadier sites aretied into pipelines, leaving more challenging sites forpotential mitigation, and decisions by individual opera-tors to vent rather than flare. Each of these potentialfactors is investigated in the analysis below. Understand-ing the relative importance of any of these parameters inexplaining the observed annual trends is critical to under-standing potential opportunities and barriers to futuremitigation.

Geographic Distribution of Flaring and VentingActivity in Alberta

The geographic distribution of flared and vented volumesof solution gas is shown in Figure 3. The quantities of gasemitted within each interval of geographic coordinates(latitude and longitude) are represented by both the colorand height of the polygons, according to the scale on theright-hand side of the figures. The interval size is half adegree in both latitude and longitude. Figure 3a showsthat flaring activity is spread throughout a large portionof the province with only a few distinguishable “hotspots” of greater intensity. In contrast, Figure 3b showsthat venting activity is overwhelmingly localized to theeast-center of the province, near the city of Lloydminster.Resources in this region are predominantly bitumen andheavier oils, which typically have lower GORs that restrictthe economic feasibility of conservation options. Heavyoil wells also can have faster production decline rates thatresult in shorter production lives, which have a negativeimpact on the economics of conservation. Finally, lowerGORs also mean that gas volumes produced at individualwells would be lower, which could affect the ability offlares to sustain stable combustion when being fed fromthese sources as further considered below. Figure 3c mapsthe change in vented volumes between 2005 and 2008,demonstrating that the bulk of the increase in venting has

Figure 2. Monthly volumes of flared and vented solution gas fromoil and bitumen batteries in Alberta for 2002–2008. Volumes arerepresented as symbols and read on the left vertical axis; percent-ages are represented as lines and read off the right vertical axis.

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also occurred in this region. Because this increase is alsogenerally correlated with regional changes in numbersof active batteries shown in Figure 3d, the overall trendin the Province toward increased proportion of ventedgas is at least partially attributable to industry-widechanges in activity. Figure 3d also shows the outline ofwhat was considered the “Lloydminster region” forthe purpose of this discussion. This region was definedas being between �110.000 ° and �112.200 ° longitude

and between 51.794 ° and 55.111 ° latitude, encom-passing the ERCB’s Wainwright field center region andcontinuing north to the seventieth township.

Battery Size/Volume DistributionsFigures 4 and 5 show histograms of the number of oil andbitumen battery sites in Alberta, sorted by their totalannual volumes of gases flared or vented in 2008. Figure 4shows reported flared volumes, and Figure 5 shows vented

Figure 3. Map of the Province of Alberta showing localized annual flare and vent volumes at solution gas batteries: (a) flared volumes in 2008;(b) vented volumes in 2008; (c) difference in vented volumes from 2005 to 2008 (note the different scale that accommodates negative numbers);and (d) change in numbers of active batteries, with superimposed white border to delineate the defined Lloydminster region.

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volumes for physical batteries only. Also shown on thesefigures are lines indicating cumulative percentages of par-ticipating batteries (dashed), as well as cumulative per-centages of flared or vented gas. Note that the horizontalaxes are in logarithmic scale, which serves to illustrate thewide range of emitted volumes from these sources.

As shown in Figure 4, annual volumes being flared atbatteries in 2008 varied by more than 5 orders of magni-tude. Only 3 of the 2360 batteries that reported flaringwere paper batteries, and the volumes reported by thesethree were small enough (�0.5% of the total gas flared)that their inclusion did not alter the shapes of the distri-butions shown in the figure. The distribution of flaredvolumes is highly skewed, such that there are many moresmaller sites than larger ones. This skewness of the vol-ume distribution is demonstrated by the discrepancy be-tween the median value of 32 � 103 m3/year and the meanvalue of 129 � 103 m3/year. The large number of smallervolume batteries suggests that conservation-based mitiga-tion may not be possible at a significant number of bat-teries. Discounting any additional volumes of gas beingvented at these same batteries, 91.2% of the sites in Figure4 fall below the ERCB threshold of required economicanalysis for conservation. Conversely, these same datasuggest there may be significant opportunities for achiev-ing reductions in flared volumes if conservation strategieswere implemented at only a few of the larger battery sites.Inspection of the curves for cumulative fraction of batter-ies and cumulative volumes of gas flared reveals that thelargest 236 sites (10%) flare �62.5% of the gas, the largest118 sites (5%) flare 48% of the gas, the largest 5 sites flare9%, and the single largest site flares 3%. These data aresummarized in Table 2. Thus, finding mitigation solu-tions for just the largest 118 sites could almost halve thevolumes being flared in the Province. The fact that thesepotential opportunities are still apparent in 2008 is per-haps one indication why the trend in Figure 2 towardreduced flared volumes is continuing.

Reported vented volume data reveal similar distribu-tion trends, as shown in Figure 5 (which plots data for

physical batteries only). For the venting volume data, theeffects of aggregate reporting as paper batteries are non-negligible. Although only 5% of the 4263 sites reportingventing activity in 2008 were paper batteries, these 213sites contributed more than one-third (35.7%) of the an-nual total gas vented in the Province. Indeed, four of thefive largest venting sites are paper batteries, which there-fore play a fairly significant role in the overall picture ofsolution gas venting. Because it is not possible to know inthe current data how the large paper batteries are distrib-uted among actual physical vents, it is difficult to deter-mine how amenable these sites might be to conservation.Nevertheless, the volumes are sufficiently large that thesesites would be worthy of site-specific economic analyseseven considering that sites associated with heavy oil pro-duction may have shorter production lives. Alternatively,even if it were only possible to convert some of thesevents to flares, significant reductions in GHG emissionsmight still be realized. Factoring in the differences in massof CO2 and methane, flaring rather than venting a givenvolume of methane would result in a factor of 9.1 reduc-tion in CO2 equivalent GHG emissions.

Focusing on physical batteries only, from the datashown in Figure 5, the mean vented volume is 61 � 103

m3/year and median vented volume is 8.8 � 103 m3/year,which indicate a very highly skewed distribution. Relativeto flared volumes, there are greater numbers of smallervents even though the size data still span 5 orders ofmagnitude. It is important to note that the percentagevalues indicated on Figure 5 are of the totals for physicalsites (i.e., excluding paper batteries), rather than all vent-ing sites, and represent only about two-thirds of the totalvented volume. Nevertheless, as summarized in Table 2,the largest 10% of physical venting sites contribute 44%of the total gas vented in the Province (68% of the gasvented at nonpaper batteries), the largest five physicalsites vent 4.7% of all the gas vented (7.3% of gas vented atphysical batteries), and the largest single physical sitevents 1.2% of the total gas vented in the Province. Al-though only 3.4% of venting physical batteries are abovethe threshold for required annual economic evaluation

Figure 5. Vent size histogram, excluding paper batteries. Cumu-lative percentages are the totals for physical sites only.

Figure 4. Histogram of volumes flared at oil and bitumen batteriesin Alberta in 2008.

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via ERCB D60 (disregarding any additional flaring activityat these sites), these sites account for nearly one-third ofthe vented gas in the Province (29.4%). D60 also statesthat the ERCB “…may investigate vented volumes of 500m3/day, or even lower, if it appears that stable combus-tion of the gas may be feasible.”23 As indicated on Figure5, the majority of venting physical battery sites (92.7%)fell below this threshold; however, the 7.3% above ac-counted for 39.4% of all gas vented from oil and bitumenbatteries in Alberta.

Site-by-Site Variability of Flared and VentedVolumes

Although the magnitude of total gas volumes being pro-cessed at a battery would certainly guide any potentialopportunities for mitigation as discussed above, the vol-ume variability at a particular site is also an importantconstraint on the ability to implement different solutiongas conservation strategies. For example, at sites whereproduction is cycled among a number of wells, volumesdirected to a flare or vent may vary significantly withoperating conditions. Similarly, even a site that is tiedinto a pipeline for conservation may be forced to flare orvent large volumes for a short period of time in the eventof a compressor failure or a downstream upset. In con-trast, a smaller battery site that operates a flare continu-ously at low flow rates could process volumes of gas on anannual basis similar to those of either of the previous twoexamples, but this steadier site is likely to be more ame-nable to conservation. The potential importance of thesedifferences can be examined by investigating the variabil-ity of all flaring and venting batteries in the Province.

The most common way of quantifying variability isto calculate the standard deviation of monthly gas vol-umes. However, as discussed by Johnson et al.,5 this maynot be the most useful parameter if monthly volumes arenot normally distributed and the goal of quantifying vari-ability is to determine the ease with which a device suchas a compressor might be sized to handle the full range offlows. Instead, an alternative measure such as the nomi-nal turndown (NTD) ratio, defined as the ratio of themaximum monthly volume to the mean monthly vol-ume, may be used to estimate the range of flows thatwould need to be handled to capture the majority of theavailable gas. This NTD ratio is related to the deviation ofthe maximum value to the mean value (DMM), which hasbeen similarly used.5 Mathematically, the following istrue:

NTD �Maximum volume

Average volume� DMM � 1 �

�Maximum volume � Average volumeAverage volume � � 1

(1)

Thus, an NTD ratio of 1 (DMM value of 0) means that a siteshowed no variability, whereas an NTD ratio of 2 (i.e., DMMof 1) means that the maximum reported value was twice theaverage.

Components such as compressors used to direct solu-tion gas into pipelines for conservation or pipelines them-selves are typically limited by a maximum instantaneousflow rate. Compressors in particular tend to have a rathernarrow operating window, with a turndown ratio (the ratioof maximum sustainable flow rate to the minimum flowrate required for efficient operation) of perhaps 2 or 3:1. Aflare, on the other hand, is limited only by combustionstability and can have turndown ratios as high as 100:1, andbecause vents do not have a minimum flow requirement,their turndown ratios are effectively infinite.

Figures 6 and 7 show cumulative 2008 flared andvented volumes, respectively, sorted from largest to small-est facilities, for several values of maximum NTD. These

Table 2. Statistical summary of 2008 reported flared and vented volumesa

Flaring at AllBatteries

Flaring at PhysicalBatteries

Venting at AllBatteries

Venting at PhysicalBatteries

Total 305,179 303,531 381,916 245,356Mean 129 129 90 61Median 32 32 10 9Top 10% sites 190,751 (62.5) 189,999 (62.6) 281,568 (73.7) 167,706 (68.3)Top 5% sites 146,236 (47.9) 145,923 (48.1) 228,199 (59.8) 131,009 (53.4)Top 5 sites 27,268 (8.9) 27,268 (9.0) 25,581 (6.7) 17,809 (7.3)Largest site 9461 (3.1) 9461 (3.1) 9590 (2.5) 4482 (1.8)

Notes: aVolumes are given in 103 m3 (percentage). Percentages listed are of the total of that category.

Figure 6. Flare variability as a function of flare size in 2008, in orderof largest to smallest.

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NTD values were calculated for each battery using allavailable data in the period of 2002–2008. Months withzero reported volumes were not included in the averagebecause it was reasoned that in this scenario compressorequipment used for conservation could simply be cycledoff. Although the variability of individual sites could re-strict the viability of some conservation options, inspec-tion of Figure 6 reveals, for example, that approximatelyone-third of batteries had NTD values of 2 or less, andthese accounted for more than 30% of the gas flared in2008. It should be noted that these graphs were derivedfrom data reported on a monthly basis, and day-to-dayvariability could be higher or lower depending onwhether monthly reporting had an averaging effect ondaily data or if instead it exaggerated variability at sitesthat did not produce 100% of the time. Nevertheless,more than 85% of solution gas flaring in 2008 occurred atbatteries with NTD ratios of 6 or less, which could behandled by high turndown compressors or compressorsin parallel. Variability in the venting data shown in Figure7 is generally lower. In this case, more than 90% of vent-ing takes place at batteries with NTD ratios of 6 or less.

Trends in VariabilityA potential limit to continued reductions in flaring andventing is if steadier sites were being preferentially selectedfor mitigation. In time, this would leave proportionatelymore unsteady sites, reducing opportunities and/or increas-ing technical and economic challenges of further reduc-tions. Figure 8 summarizes an analysis of annualized trendsin variability of monthly flare and vent volumes, whichinvestigated this possibility. Flare and vent volumes areshown in Figures 8a and 8b, with superimposed line plotsshowing volumes attributable to sites with different levels ofvariability measured in terms of NTD ratio. Figures 8c and8d show percentages of total gas flared and vented at siteswith different NTD ratios. Perhaps surprisingly, from theflaring data (Figures 8a and 8c), it is apparent that the re-ductions being made in total flaring volumes are being

made throughout all NTD levels, with the bulk of the earlier(2002–2004) reductions occurring at more variable sites. Infact, the proportion of sites with NTD ratios less that 3actually increased slightly from 2002 to 2008, althoughthere was less than 10% variation at each level. This resultsuggests that preferential mitigation of steadier sites is notoccurring. Coupled with the fact that at the start of 2009there were still many large flaring batteries, this impliesthere are still very good prospects for significant reductionsin flared volumes in Alberta.

In the corresponding venting figures, initial reductionsfrom 2002 through 2005 seem to have slightly reduced theproportion of venting batteries with NTD ratios of 2 or less.The fraction in this category actually hit a minimum in2006. However, it also seems that most additions after 2005were of relatively steady sites in the NTD ratio of 1.5–3range, and the proportion of steadier sites in 2008 was ac-tually slightly greater than it was in 2002. This again sug-gests that overall opportunities for venting reductions arenot limited by any form of selective mitigation of steadiersites. Moreover, in terms of volume variability, recent in-creases in venting seem to be associated with low NTD ratiosites that, in general, would be well suited to conservationstrategies using standard compression equipment. Finally,as noted earlier, simply choosing to flare rather than ventsome of this gas at low NTD ratio sites could lead to signif-icant GHG emission reductions.

Analysis of Trends in Flaring to Venting RatiosReferring again to Figure 2, it was observed that sinceJanuary 2005, the proportion of gas being vented hasincreased steadily, i.e., volumes of venting increased,whereas total gas volumes have remained relativelyconstant. This trend is partially explained by thechanges in activity levels by region as discussed above(i.e., growth of production in heavier oil near Lloyd-minster and decline in other areas). However, it is alsopossible that some existing batteries could be extin-guishing their flares and venting gas instead. Thismight occur in situations in which production and/orgas volumes were declining, such that the amount ofgas available to be directed to a flare was insufficient tosustain combustion. As an alternative, it is also possiblethat some operators may be choosing to vent gas ratherthan flare it. To investigate these possibilities, an ana-lytical procedure was devised to search for instances ofstatistically significant changes in flare/vent ratios atall individual batteries active during the period of2005–2008.

For each monthly report from each battery, the “flaredfraction” (i.e., volume flared/total volume flared andvented) was calculated. The flared fraction data from theyears 2005 and 2008 were then compared with a look forinstances of statistically significant increases in the propor-tion of gas being vented at a battery. Two-sample t tests wereperformed such that a null hypothesis, that there was noreduction in the flared fraction, would be rejected if themore recent data had a statistically lower flared fractionthan earlier data. To account for the possibility that a po-tential switch in operating practice at a battery might occuranytime during 2005 or 2008 (and not only in the interven-ing months), the statistical significance test was applied

Figure 7. Vent variability as a function of vented volumes in 2008,in order from largest to smallest.

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iteratively at all potential split points in time. To accomplishthis, the monthly flared fraction data from 2005 and 2008were iteratively divided at all potential points in time tocreate paired data sets for statistical testing. As an example,for a test split point occurring sometime during 2005, databefore that point were compared with 2008 values; con-versely, for a split point during 2008, data from 2005 werecompared with 2008 data after that point. A “complete”data set of monthly production reports from 2005 and 2008would thus have 21 potential split points to test (i.e., theexistence of any statistically significant shifts in flared frac-tion starting from March 2005 to November 2008 wereconsidered). The dividing point that returned the most sig-nificant difference (i.e., the minimum P value), if any, wasrecorded.

Of the 9350 batteries that reported flaring or ventingbetween 2005 and 2008, 382 (4.1%) were preliminarily iden-tified as having a statistically significant (at a significancelevel of 0.05, i.e., 95% confidence) drop in the flare ratioover time. Of these, 5 were paper batteries. However, beforedrawing any conclusions, one must first examine what ismeant by “statistically significant,” as well as consideringthe volumes these batteries represent. First, the issue of in-terpreting statistical significance is addressed. The null hy-pothesis t test described above only determines whetherthere is a measurable difference between the two datasets relative to the inherent variability in the data,

without separate consideration of the relevance or mag-nitude of this difference. Therefore, a further minimumdifference in the flared fraction criterion was applied,such that small changes in flared fraction (whetherstatistically measurable or not) were neglected. Al-though the choice of this magnitude criterion is sub-jective, it is necessary to permit correct interpretationwithin a practical context. It is also noted that higherconfidence intervals were considered in a preliminaryanalysis, and the conclusions were unchanged. The fi-nal approach taken (95% confidence interval with aseparate criterion to filter and test for effect magnitude)was preferred because choosing a higher confidenceinterval tends to reject both good and bad data, whereasthe minimum magnitude criterion effectively weedsout chance events that persist with the slightly lower95% confidence interval. The importance of consider-ing effect size in conjunction with statistical signifi-cance is succinctly discussed by Nakagawa.25

For the purpose of this analysis, an absolute reductionin flared fraction of 0.2 or greater was considered practicallysignificant. This threshold reduced the number of prelimi-narily identified batteries from 382 to 328. Thus, by thesecriteria, it can be observed that 3.5% of the 9350 batteriesreporting flaring or venting throughout 2005 and 2008 hadstatistically measurable and practically significant increasesin the proportion of gas being vented.

Figure 8. Volume variability trends in the years 2002–2008: (a) flared gas volume; (b) vented gas volume; (c) percentage of flared volume;and (d) percentage of vented volume.

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Figure 9 shows the monthly volumes and percentagesof gas flared and vented from this subset of batteries. Al-though the total volume of gas handled at these sites isrelatively small (37 million m3 or 5.4% of total for 2008), thetrend of decreasing flared fraction is quite clear, demonstrat-ing the validity of the statistical approach. In fact, evenwithin the context of an overall decline in total volume,there is an absolute increase in the volume of gas beingvented at these sites. As noted above, one potential expla-nation for this change is that the reduction in total volumesat these batteries had resulted in there being insufficient gasavailable to sustain combustion in a flare.

Figure 10 shows a histogram of average monthly vol-umes for 2008 (i.e., total volume reported in 2008/numberof reporting months) at the 328 identified sites of interest.Also shown on the graph are cumulative percentages of thenumber of sites and their volumes, in a manner similar tothat in Figures 4 and 5 above. Finally, several vertical lineshave been superimposed on the figure to indicate the mean,median, and 10th and 90th percentile flare volumes for theentire sample of battery sites in 2008, as well as lines corre-sponding to the ERCB threshold for required economic eval-uation (900 m3/day) and the threshold at which ERCB “mayinvestigate vented volumes…if it appears that stable com-bustion of the gas may be feasible.”23 Approximately 13% ofthese sites processed monthly volumes smaller than that ofa 10th percentile flare, implying that at these specific sites,increased venting may be a result of limits imposed by flamestability associated with reduced volumes. Conversely, 43%of these sites were larger than the median flare size and 19%handled volumes above the ERCB “may investigate” thresh-old. These data suggest that volume-related limits of flamestability are unlikely to be the reason for increased ventingat these sites.

Attribution of Changes in Vented Volumes2005–2008

In the detailed discussion presented above, several potentialexplanations for the trend of increased venting from 2005 to2008 in Alberta were separately considered and investigated.Figure 11 compiles the results of this analysis to show the

relative significance of each of these in defining the overallpatterns of solution gas venting in Alberta. Batteries thatexisted in 2005 showed a dramatic decrease in totalmonthly vented volumes through to the end of 2008. This

Figure 9. Monthly flared, vented, and total gas volumes of batteriesshown to have a statistically significant change in flared fraction of atleast 20% from 2005 to 2008.

Figure 10. Distribution of 2008 total volumes for batteries withstatistically significant increases of greater than 20% in proportion ofgas being vented during the period 2005–2008. Percentages areread on the right vertical axis.

Figure 11. Attribution of change in vented gas volumes relative toJanuary 2005.

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could be attributed to both declining production and in-creased conservation at these sites. However, this decreasewas overwhelmed by the increases in vented volumes fromnew batteries, which was dominated by new production inthe Lloydminster area. As noted previously, production inthe vicinity of Lloydminster is generally associated withheavier oils/bitumen, and the increase in vented volumesseems to be closely tied with this change in activity patternsfor the Province. Finally, although measurable on Figure 11,the increase in venting associated with batteries changingthe proportion of gas being flared and vented is much lesssignificant in terms of the overall trends.

CONCLUSIONA detailed analysis of production data for 18,203 active oiland bitumen batteries in Alberta from January 2002 toDecember 2008 has been completed to examine recentactivity patterns in solution gas flaring and venting aswell as potential explanations for these trends. Althoughoverall volumes being flared and vented were 31.9% lowerin 2008 than in 2002, since 2005 flare volumes haveremained steady while vent volumes have risen signifi-cantly (31.2% greater in 2008 relative to 2005). However,the distribution of gas volumes being flared and vented atindividual batteries is very highly skewed, such that smallnumbers of batteries flare or vent a majority fraction ofthe Provincial total. Furthermore, a majority of flaring andventing batteries were revealed to be combusting or releas-ing relatively steady volumes of gas on a monthly basis.Together, these data imply that significant mitigation op-tions should be possible by seeking solutions for a relativelysmall number of batteries in the Province. Moreover, anal-ysis of monthly data over the 7-year span from 2002through 2008 suggests that these better-suited mitigationsites were not being preferentially removed from the pool ofactive batteries, which to date would not be inducing anybarriers to further or renewed mitigation. Finally, the recentrise in venting activity has been largely attributed to newproduction activity of predominantly heavier oils in theLloydminster region of the Province. The success of futuremanagement and mitigation strategies will depend on find-ing specific solutions in this region. The particular analytictechniques developed for this analysis could also be appliedin the study of mature and emerging petroleum fields indifferent parts of the world.

ACKNOWLEDGMENTSThe authors are indebted to James Vaughan, Jill Hume,and Jim Spangelo of the Alberta Energy Resources Con-servation Board, who worked very hard in accommodat-ing the requests for large amounts of data necessary forthis analysis. The authors also appreciate the support ofMichael Layer, Natural Resources Canada, who providedhelpful context to aspects of the data.

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About the AuthorsMatthew Johnson is the Canada Research Chair in En-ergy & Combustion Generated Pollutant Emissions andan Associate Professor at Carleton University. AdamCoderre has an M.A.Sc. degree in Mechanical Engineer-ing from Carleton University and is actively engaged inseveral projects related to quantifying emissions as-sociated with upstream oil and gas production. Pleaseaddress correspondence to: Matthew R. Johnson, Me-chanical & Aerospace Engineering, Carleton Univer-sity, Ottawa, ON, Canada K1S 5B6; phone: �613-520-2600, ext. 4039; fax: �613-520-5715; e-mail:[email protected].

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http://dx.doi.org/10.3155/1047-3289.59.9.1111

Johnson2011-An Analysis of Flaring and Venting Activity in the Alberta Upstream Oil and Gas Industry

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