# Shale Gas Production: Potential versus Actual GHG Emissions

Francis O’Sullivan and Sergey Paltsev



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Printed on recycled paper1 Shale G as P roduction : P otential v ersus A ctual GHG E missions

Francis O’Sullivan *† and Sergey Paltsev * ‡

Abstract

Estimates of greenhouse gas (GHG) emissions from shale gas production and use are controversial. Here we assess the level of GHG emissions from s hale gas well hydraulic fracturing operations in the United States during 2010. Data from each of the approximately 4,000 horizontal shale gas wells brought online that year is used to show that about 900 Gg CH4 of potential fugitive emissions were generat ed by these operations, or 228 Mg CH4 per well

— a figure inappropriately used in analyses of the GHG impact of shale gas. In fact, along with simply venting gas produced during the completion of shale gas wells, two additional techniques are widely used to handle these potential emissions, gas flaring, and reduced emissions “green” completions. The use of flaring and reduced emission completions reduce the levels of actual fugitive emissions from shale well completion operations to about 216 GgCH4, or 50 Mg CH4 per well, a release substantially lower than several widely quoted estimates. Although fugitive emissions from the overall natural gas sector are a proper concern, it is incorrect to suggest that shale gas

- related hydraulic fracturing has substantially altered the overall GHG intensity of natural gas production.

Contents

1. INTRODUCTION

................................ ................................ ................................ ................... 1 2. HYDRAULIC FRACTUR ING AND GHG EMISSION S

................................ ...................... 2 3. ANALYSIS

................................ ................................ ................................ ............................. 3 4. CONCLUSIONS

................................ ................................ ................................ ..................... 7 5. REFERENCES

................................ ................................ ................................ ........................ 8 APPENDIX

1. INTRODUCTION
Over the past decade, economically recoverable shale gas has transformed the U.S. natural gas industry, with some analysts characterizing i t as a “revolution” (Deutch, 2011; Jacoby et al.

, 2012). With shale driven growth, the U.S. has become the world’s largest gas producer (IEA, 2011). The low gas prices that have accompanied this production boom have led to a renewed growth in gas demand by industrial users, a recovery viewed as extremely unlikely just a decade ago. The rise of shale gas has not been without controversy, however, with important concerns raised regarding water pollution (Osborn et al. , 2011), greenhouse gas (GHG) emissions,

p articularly those related to hydraulic fracturing (Howarth et al. , 2011a ; Howarth et al., 2011b ; Howarth et al.

, 2012), and uncertainty in estimates of the resource scale (Jacoby et al. , 2012; Urbina, 2011; MIT, 2011; Lee et al. , 2010). In this analysis we focus on the issue of fugitive GHG emissions associated with shale gas fracturing and provide estimates of potential and actual
emissions.

* MIT Energy Initiative, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA

. † Corresponding author. Email: frankie@mit.edu , Tel: 617

- 715

- 5433

. ‡ MIT Joint Program on the Science and Policy of Global Change, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge MA 02139, USA.2

2. HYDRAULIC FRACTURING AND GHG EMISSIONS
The economic production of shale gas is only possible through the use of hydraulic fracturing
to increase production rates from the extremely low

- permeability shale formations. The
h ydraulic fracturing process has two main stages: injection and flowback. During injection, a slurry made up of a carrier fluid, typically water, and a proppant agent, typically san d, is forced into the well at pressures significant enough to induce fractures in the reservoir rock. These propped fractures allow gas in the formation to flow from the well at economically acceptable rates. After the injection phase is completed, flowbac k takes place. Here some of the initially injected fluid returns to the surface over the course of a week or more. During flowback, the well also begins to produce gas. It is the amount of this gas, and how it is handled, that has been
central to the debat e about the GHG intensity of shale development. In 2011, the EPA revised upwards its GHG inventories for the natural gas system (EPA, 2011), and some have attributed this increase to the expanded production of shale gas and the associated increase in hydra ulic fracturing. It has been argued that large amounts of gas are directly vented to the atmosphere during flowback, and that this means shale gas has a significantly higher GHG intensity than conventional gas production (Howarth et al. , 2011a, 2011b). In fact, with some specific assumptions about the global warming potential of gas it has been suggested that the GHG impact of shale gas might be greater than that of coal on a lifetime basis (Howarth et al. , 2011a, 2011b). This perspective has been widely ar ticulated via popular media (e.g., Soraghan, 2011; McDonald, 2011). Debate regarding t his issue has been added to by research published by NOAA scientists (Petron et al. , 2012) that studied methane and other fugitive GHG levels in air samples taken in
Col orado’s Denver

- Julesburg oil and gas basin. Their results suggest that fugitive emissions in Colorado’s Weld County during 2008 amounted to 3.8% of the county’s total gas production that

year . The study area, the Denver

- Julesburg Basin is a tight sandstone formation that produces appreciable amounts of both gas and oil. In 2008, the year of the study, there were 850 tight gas
wells and 1583 oil/condensate wells drilled in the Denver

- Julesburg are a (HPDI, 2012)

. An important point regarding the study is that it assessed fugitive emissions levels from the entire gas and oil production system in the basin, which includes many complex upstream and midstream systems widely known as fugitive emissions sources including gathering pipelines, compressor station and c ondensate tanks (EPA, 2012a; EPA, 2011). Nevertheless, some have interpreted the NOAA analysis as a quantification of fugitive emissions resulting from hydraulic fracturing alone (Tollefson, 2012)

. The conclusions of Howarth et al. (2011b), have been quest ioned by some analysts (DOE, 2011; Cathles et al. , 2012), and several groups working on the topic have come to different conclusions regarding the relative GHG impact of shale gas. Burnham et al. (2011) concludes
that the life

- cycle GHG emissions from shal e gas are slightly less than that of conventional gas,
Weber et al. , (2012) suggest they are approximately equal, while Jiang et al. (2011), Stephenson
et al. (2011) both conclude that shale gas has a life

- time GHG impact that is slightly higher than
that of conventional gas. All of these groups do however conclude that the GHG impact of3

electricity generated using shale gas is significantly less than that of generated with coal.
Howarth et al. , stand by their conclusion s (Howarth et al. , 2012), pointing ou t the significant upward revision in EPA estimates of fugitive emissions from unconventional wells in the EPA’s 2011 inventory (EPA, 2011). Their conclusions are also supported, at least in the case of Barnett shale wells, by the analysis in Hultman et al. (2011).

3 . ANALYSIS
Analysis of this controversy begins with quantification of potential emissions produced during well flowback. This requires knowledge of the duration of the flowback stage, and the rate of gas production during that period. The EPA ass umes that the flowback period lasts from 3 to 10 day s (EPA, 2011)

. A recent i ndustry

- sponsored survey suggests 3 to 8 days ( ANGA, 2012 ). The analysis of Howarth et al. , (2011a) assumes 9

- days for the wells in the Barnett shale and 10 days in the Haynesvill e shale. Here we use a 9

- dayflowback period for wells in each of the major shale plays. Although it is certain that flowback durations vary from well to well, our 9

- day assumption is at the conservative end of the reported range. Measured data on the rate of flowback from Haynesville shale wells reported by Fan et al. (2010) shows that within 9

- 10 days, the level of fluid production falls by ~75%, and this confirms that 9 days is a reasonable estimate. We assume that gas production during flowback from a gi ven well can be modeled as ramping linearly from zero at flowback initiation to the peak recorded production rate for that well at flowback completion. This assumption is supported by data presented during a recent EPA workshop (EPA, 2012b), and by both si mulation results and recorded gas production rates during the flowback of shale wells reported by Fan et al. (2010). Integrating this production profile over the 9

- day flowback period yields the potential fugitive emissions estimate for each
well.
In this report we assess the level of fugitive GHG emissions resulting from the hydraulic fracturing of 3,948 horizontally drilled shale gas wells brought online in the U.S. during 2010 (HPDI, 2012), assuming a number of gas handling scenarios, which involve diff erent levels of venting, flaring and gas capture. Table 1 shows the potential emissions estimates assuming the mean well peak production rates in each shale play for 2010.

Table 1. Per

- well hydraulic fracturing

- related potential fugitive emissions from 20 10 vintage U.S. horizontal shale gas wells (Source: Authors’ calculations based on HPDI 2012)

.

Per

- well potential emissions: (1x10 3 m 3 natural gas) Barnett Fayetteville Haynesville Marcellus Woodford

Mean: 273 296 1,177 405 487

P80: 385 409 1,538 573 685

P50: 234 285 1,108 342 413

P20: 138 167 754 195 2304

The table also illustrates the substantial well

- to

- well variability in potential emission levels by showing the estimates for the 20 th , 50 th and 80 th percentile peak production rates. The peak produc tion rate data underlying the values reported in Tab le 1 can be seen in Table A 1 of the
A ppendix . The variation in initial well productivity within and between the shale plays is driven in large part by underlying geological, geo

- mechanical, geo

- chemical and petrophysical characteristics of the shale formations. Reservoir pressure, total organic content, thermal maturity, porosity and other factors can all differ within and between plays, and this in turn
results in well

- to

- well variation in productivity (Jarvine et al. , 2007; Curtis et al. , 2012; Hammes
et al. , 2011, Baihly, et al. , 2010). Aggregating the data in Table 1 for the total number of wells brought online in 2010 yields an overall estimate of hydraulic fracturing

- related potential
f ugitive emissions from the five plays of 902 Gg CH 4 . The details of this aggregation are shown
in Table 2 . For comparison, the EPA GHG inventory for the upstream gas sector estimates total 2010 fugitive emissions of 6,002 Gg CH 4

.

T able 2

. Total hydraulic f racturing

- related potential fugitive emissions from U.S. shale gas wells brought online in 2010 (Source: Authors’ calculations based on HPDI 2012)

.
Barnett Fayetteville Haynesville Marcellus Woodford All Plays

Mean per

- well potential fugitive emissions: (1x10 3 m 3 of natural gas) 273 296 1,177 405 487

—

# of horizontal wells 1,785 870 509 576 208 3,948

Total potential fugitive emissions: (1x10 6 m 3 of natural gas) 487 257 599 234 101 1,678

Total potential fugitive methane emissions: (Gg CH 4 ) 262 138 322 125 54 902

It is useful to compare the per

- well potential emissions from Table 1 to the estimated ultimate production from wells in each play. There is appreciable uncertainty regarding the level of ultimate recovery that can be expected from shale wells . Much of this is due to the limited production history of the shale resource and, as yet, not well understood mechanisms of production in ultra

- low permeability reservoirs (Anderson et al. , 2010, Lee et al. , 2010). To account for this uncertainty we assum e two well production lifetimes in this analysis; the commonly assumed 30

- year lifetime, and a more conservative 15

- year lifetime. It is important to acknowledge though that there is legitimate debate ongoing regarding whether the productive
lifetimes of t hese wells may in fact be appreciably shorter than even our 15

- year case (Berman, 2012; Hughes, 2011). The results of the comparison between potential emissions produced during flowback and estimates of ultimate recovery based on 30

- and 15

- year producing
l ifetimes are shown in Table 3 . The results indicate that in most shale plays, hydraulic fracturing

- related potential fugitive emissions represent 0.4

- 0.6% of a well’s estimated ultimate5

recovery. In the Haynesville, the ratio is higher at 0.8

– 1%, owing to the high initial production and production decline rates in that play, which are due to that particular shale’s highly over

pressured reservoir (Baihly, 2010). Should it become clear that shorter lifetimes are more representative, then the ratio of potenti al emissions to ultimate recovery will increase, though not proportionally as shale wells tend to be most productive during their early lives. Details of actual production dynamics from the ensemble of shale wells drilled sinc e 2005 can be found in section
A 2 of the A ppendix

.

Table 3. Shale gas hydraulic fracturing

- related potential fugitive emissions as a percentage of estimated ultimate recovery assuming mean well prod uction performance rates and 30

- year and 15

- year producing lifetimes (Sou rce: Authors’ calculations based on HPDI, 2012).

Barnett Fayetteville Haynesville Marcellus Woodford

30

- year lifetime 0.39% 0.39% 0.78% 0.39% 0.39%

15

- year lifetime 0.54% 0.52% 0.99% 0.53% 0.52%

The proportions of the potential fugitive emissions that are vented, flared, or captured and sold via a reduced emission “green” completion determine the actual GHG intensity of shale gas

related hydraulic fracturing. In this analysis we use specific GHG intensities for venting, flaring
and reduced emission com pletions of 13.438 kg CO 2 e, 1.714 kg CO 2 e and 1.344 kg CO 2 e respectively, based upon a 100

- year Global Warming Potential (GWP) for CH 4 . Schindell et al, (2009) argue that the use of a 100

- year integration period underestimates the actual warming impact of CH 4 and suggests that a higher GWP factor, based on a 20

- year integration period be
used instead. Because the various GHGs have different lives in the atmosphere (e.g., on the scale
of decade for CH 4 but centuries for CO 2 and thousands of years for some ot her GHG gases), the Intergovernmental Panel on Climate Change (IPCC, 2007) provides this factor for 20

- , 100

- , and
500

- year integration periods and uses 100

- year GWPs. MIT (2011) argues that 20

- year GWP would emphasize the near

- term impact of methane but i gnore serious longer

- term risks of climate change from GHGs that will remain in the atmosphere for hu ndreds to thousands years. For a comparison, the specific GHG intensities of venting, flaring and reduced emissions completions assuming a 20

- year GWP fo r CH 4 are detailed in section A 3 o f the A ppendix

. Significant opaqueness surrounds real world gas handling practices in the field, and what proportion of gas produced during well completions is subject to which handling techniques.
Diverse opinions on this question exist even within the gas industry. Some analysts state that gas companies have had a policy of not investing in gas conservation measures due to the low rate of return. By contrast, an industry survey of unconventional gas produc ers has suggested that reduced emission completions are being used on more than 90% of shale wells completions, and that in the case of those wells not subject to a reduced emissions completion, the duration of flowback is rarely more than 3 days (ANGA 201 2). Some of the contemporary analysis on shale

gas

- related fugitive emissions has not attempted to account for the impact of real world gas handling field practice. For example, in Howarth et al. (2011b) it is assumed that all potential fugitive emissions are vented. This is an unreasonable assumption, not least because some6

producing states have regulation requiring flaring as a minimum gas handling measure. The EPA in its quantification of fugitive emissions does assume a certain proportion of gas is flar ed (EPA, 2011; EPA, 2012a); however, it does not separate fugitive emission from shale wells with those from tight and other unconventional gas sources. Furthermore, the EPA analysis does not adequately assess gas capture levels, particularly in regions wh ere flaring is required. We assess several gas handling scenarios, ranging from the assumption that all potential emissions are vented (Howarth et al. , 2011b), to that suggested by a gas industry group in which 93% of potential fugitive emissions are captu red (ANGA, 2012). However, our main estimate of actual fugitive emissions is based on a “current field practice” gas

- handling scenario, where 70% of potential fugitives are captured, 15% vented, and 15% flared. This we believe is a reasonable representatio n of current gas handling practices in the major shale plays (EPA, 2012b) (Further discussions of gas handling scen arios are presented in section A 3 of the A ppendix ). Table 4 contrasts the level of per

- well actual fugitive emissions based up on the assumption of the “current field practice” scenario and the “all vented” scenario. Compared to the all

- vented analysis (Howarth et al. , 2011b), which reports emissions from Barnett as 252 Mg CH 4 /well (or 370,000 m 3 CH 4 ) and 4,638 Mg CH 4 /well (6,800, 000 m 3 CH4) for Haynesville, our mean estimates are 35.1 Mg CH4/well and 151.3 Mg CH 4 /well, respectively.

Table 4. Per

- well actual fugitive GHG emissions from shale gas

- related hydraulic fracturing in 2010 (Source: Authors’ calculations based on HPDI 2012)

. Barnett Fayetteville Haynesville Marcellus Woodford

Per

- well GHG emissions: Mg CH 4 /well (related CO 2 emissions are added based on 100

- yr CH 4 GWP)
All Vented 146.7 159.1 632.7 217.7 261.8

Current Field Practice 35.1 38.0 151.3 52.1 62.6

Beyond regul ation, the methods selected to handle gas during well completions in the field are driven by economics. In the case of conventional gas wells, the volumes of potential emissions produced during completion are very low. According to the EPA, on average, 1,0 40 m 3 CH4 (36.36 Mcf) are produced by a conventional well completion (EPA, 2010). The economic value of this gas would certainly not justify the use of a reduced emission “green” completion. By contrast, the level of potential emissions from shale wells is very large. In Howarth et al. (2011b) it is stated that 3.2% of the estimated ultimate recovery from a Haynesville shale well is produced during flowback. In that case, 3.2% of estimated ultimate recovery amounts to 6,800,000 m 3 CH4 . This is a very consid erable amount of gas and assuming a conservative long

run wellhead gas price of $4.00/MMBtu (MIT, 2011; NYMEX, 2012; EIA, 2012), simply venting, or indeed flaring this gas would amount to a revenue loss of $1.2 million for the operators. Admittedly, this i s an extreme example since the performance of the particular Haynesville well in question is not representative of a typical Haynesville well; however, even when considering mean shale well performance data, the value of gas produced during flowback
is sub stantial, and likely to warrant the cost of capture. Based on our mean estimates of potential
emissions shown in Table 1 , the gross values of capturing this gas using a reduced emission7

completion ranges from $39,000 for a Barnett well to $166,000 for a Ha ynesville well. T he aggregate gross value of the gas produced during flowback from the 3,948 shale wells considered in this study amounts to $320 million. Capturing potential emissions is not without cost, of course, but these costs appear to be relatively modest (A detailed discussion of the variability in the gross value of gas produced during flowback, and the costs associated with reduced emission compl etions can be found in section A 4 of the A ppendix .). If the cost of
reduced emission co mpletion is $1,000 per day as stated by Devon (2008) , 95% of the 2010 Barnett wells yielded positive net revenues, i.e. operators added to the value of their wells by capturing the potential fugitive emissions . Even at twice this reported capture cost, $2, 000 per day, 83% of the 2010 Barnett wells would still positive net revenues, and this trend is repeated in
the all the other shale plays. The results of a sensitivity analysis exploring the impact of reduced emissions completion costs and gas price variat ion on the 2010 Barnett shale well ensemble are shown in Figures A5 and A 6 of the A ppendix

.
4 . CONCLUSIONS
Taking actual field practice into account, we estimate that in 2010 t he total fugitive GHG
emissions from U.S. shale gas

- related hydr aulic fracturing amounted to 216 Gg CH 4 . This
represents
, 3.6 %, of the estimated 6,002 Gg CH 4 of fugitive emissions from all natural gas production

- related sources in that year (EPA, 2012 a; EPA, 201 2b ). The entire natural gas value chain is estimated to have produced 1 0,259 Gg CH 4 of fugitive emissions in 2010, or about 3.1% of the Nation’s total GHG inventory ( EPA, 2012 a; EPA, 201 2b )

. Thus under a goal of GHG reduction it is clear that increased efforts must be made to reduce fugitive losses from this system. However, it is also cl ear is that the production of shale gas and specifically, the associated hydraulic fracturing operations have not materially altered the total GHG emissions from the natural gas sector. Furthermore, for the vast majority of contemporary shale gas wells,
th e revenues gained from using reduced emissions completions to capture the gas produced during a typical flowback cover the cost of executing such completions.

Acknowledgements
The Authors wish to thank Henry Jacoby for his guidance and input in the develo pment of this analysis and Audrey Resutek for her help with the manuscript. We are also thankful to three anonymous referees of the paper for their useful comments and suggestions. This work was not supported by any sponsored research funding from commerci al or other entities. MIT, where the authors are employed, receives funds from numerous industrial and government sources, but the work on this paper received no such funding.8

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– 5695.1 APPENDIX 1

Contents

A1. SHALE GAS PRODUC TION GROWTH IN THE U NITED STATES

.............................. 1 A2. VARIABILITY IN S HALE WELL PRODUCTION PERFORMANCE

............................ 1 A3. GHG INTENSITY OF FLOWBACK GAS HANDLIN G METHODS

............................... 5 A4. ECONOMIC MOTIVAT ION FOR FLOWBACK GAS CAPTURE IN SHALE PLA YS

.. 9 A5. REFERENCES

................................ ................................ ................................ ................... 13

A 1 . SHALE GAS PRODUCTI ON GROWTH IN THE UNI TED STATES
Natural gas production in the United States has undergone a renaissance over the past 5

– 6 years as a result of shale gas ( De utch, 2011 ). Between 2005 and 2010 the contribution from shale gas to total U.S. marketed gas production rose from less than 2% to more than 20%. Based upon EIA data, 2011 has set an all time record for U.S. production as the result of shale gas growth,
wi th total daily dry output for the first ten months of the year averaging 1.77 Gm 3 /day (62.7 Bcf/day).

T he remarkab le shale gas production levels seen over the past number of years have been supported by a relatively small number of plays, the main ones being the Barnett shale, in Texas’ Fort Worth basin, the Fayetteville and Woodford shales of the Arkoma basin in Arka nsas and Oklahoma, the Haynesville shale on the Texas Louisiana boarder, the Marcellus shale in the Appalachian basin, and of late the Eagle Ford shale located in southwest Texas. Figure A 1 illustrates the growth in gas output from these shale gas plays si nce 2000. Until 2009 the overwhelming majority of total U.S. shale gas production came from the Barnett shale; however, in the last two years that situation has changed and production from other plays, particularly the Haynesville and Marcellus is now grow ing rapidly.

A 2. VARIABILITY IN SHALE WELL PRODUCTION PERF ORMANCE
The shale plays currently being developed in the U.S. do not constitute a homogenous resource. Each play has its own set of particular geological, geo

- mechanical, geo

- chemical and petrophysi cal characteristics , and variability in factors including reservoir pressure, total organic content, thermal maturity, porosity, the presence of natural fractures along with a lack of knowledge regarding shale rocks’ fundamental production mechanisms means that the performance of individual wells can differ substantially both within and between plays ( Jarvine
et al. , 2007; Curtis et al. , 2012; Hammes et al.

, 2011; Baihly et al. , 2012 )

. Two metric s widely

use d in describing shale well performance are the initia l production (IP) rate and the production decline rate. Together these combine to determine the ultimate recovery (UR) from a well. The IP rate variability among horizontal wells brought on production in the five most active U.S. shale gas p lays in 2010 is given in Table A 1 . Reviewing the data in the table reveals the

1 This is an appendix to O’Sullivan and Paltsev (2012): Shale Gas Production: Potential versus Actual GHG Emissions , MIT Joint Program on the Science and Policy of Global Change Report 230 ( http://globalchange.mit.edu/files/document/MITJPSPGC_Rpt230.pdf )2

extent of both the intra and inter

- play well

- to

- well IP rate variability. In each play the P80 IP

rates are 2

– 3X the P20 rates, while between plays the mean IP rates vary by up to 4.3X. Similar trends can also be observed in IP rate data for prior years.

Figure A1. Growth in natural gas production from U.S. shale plays between 2000 and 2010 ( Source: HPDI, 2012).

Table A1. IP rate variability of the horizontal wells brought on production during 2010 in the Barnett, Fayetteville, Haynesville, Woodford and Marcellus shale plays (Source: Authors’ calculati ons based on HPDI, 2012).

IP Rate: 1x10 3 m 3 /day Shale Play # of H. Wells Mean P80 P50 P20

Barnett 1,785 60.6 85.5 52.1 30.6 Fayetteville 870 65.7 90.8 63.4 37.1 Haynesville 509 261.5 339.6 246.2 167.5

Woodford 208 108.1 152.3 91.7 51.2

Marcellus 57 6 90.0 127.4 76.1 43.3

The Barnett shale play provides an excellent basis for examining this year

- to

- year IP rate variability due to its relatively longer production history and la rger inventory of well. Figure A 2 plots the IP rate cumulative probability functions for each vintage of horizontal wells drilled in the Barnett from 2005 to 2010. Each vintage displays the well

- to

- well IP rate variability described above, however, it is also clear that the on average, IP rates have been increasing incrementally year

- on

- year. In 2005, the mean, P90 and P10 IP rates for the 720 horizontal wells that were brought on production were 48,500, 93,050 and 14,300 m 3 /day respectively. By 2010 those same figures had increased to 60,700, 110,900 and 21,500 m 3 /day. Many fact ors play a role3

in this IP rate shift; however, increased horizontal well lengths and more effective fracturing are likely to be some of the most important.

Figure A2. Cumulative probability functions for initial production rates of horizontal wells dril led in the Barnett shale from 2005 to 2010 ( Source: HPDI, 2012).

The rate at which a well’s gas production changes over time is described by the well’s decline characteristic or “type curve.” Data on shale well decline characteristics is still sparse due to the limited time most wells have been producing. However, the data that is available reveals some interesting trends. The first is that in general, shale well output tends to drop by 60% or more
from the IP rate level over the first 12 months. The secon d is that the available longer

- term production data suggests that levels of production decline in later years are moderate, often less than 20% per year. Figure A 3 shows the normalized decline characteristics for each vintage in
the Barnett shale from 2005 to 2010. Although there is some variation, overall, the normalized decline characteristics have been very similar year

- to

- year. All the shale plays currently in production have qualitatively similar decline characteristics, i.e. significant production dec line during the first year of production followed by more moderate rates of decline in subsequent years. Nonetheless, there are meaningful differences between plays
as shown in Figure A 4 , which plots the normalized 2009 decline characteristics of the Barne tt, Fayetteville and Haynesville plays. The Barnett and Fayetteville plays have relatively similar year 1 decline rates of 55

– 60%.4

Figure A3. Normalized production decline characteristics for Barnett shale well vintages from 2005 to 2010 ( Source: HPDI, 2012 ).

Figure A4. Normalized production decline characteristics for 2009 vi ntage horizontal wells in the Barnett, Fayetteville and Haynesville shale plays (HPDI, 2012).

The Haynesville decline characteristic is different, with a year 1 production rate decline of ~75%. Understanding the differe nces in decline characteristics among shale plays is very complex and requires consideration of both reservoir and well completion factors. However,5

insights do exist regarding the variability. For example, in the case of the Haynesville, its very high yea r 1 decline rates have been linked to the highly over

- pressured nature of the reservoir and the likelihood of pressure dependent permeability resulting in a temporally progressive reduction in gas conductivity (Thompson et al.

, 2010; Baihly et al. , 2010 ). Determining how much gas individual shale wells will produce over their lifetime is also a challenging problem muddied by many uncertainties. To date, estimates of shale well UR have been made by combining IP rate data with long

- term projections of well production decline characteristics. These decline projections are often extrapolated from shorter

- term decl ine data shown in Figures A 3 & A 4. These “type curve” me thods for estimating shale well UR are controversial as they are based on techniques developed to assess the UR from wells in reservoir boundary dominated flow regimes (Lee et al.

, 2010; Anderson et al. , 2010 ). The complexity of these issues is beyond the scope of this paper; however, one outcome is that the fitting of shale well decline rate data has in some instances yielded parameters outside the limits suggested as reasonable by the theory, and the practical result of this is that UR estimates based on these type curve methods must be viewed with some caution, particularly in terms of possible
overestimation ( Lee et al.

, 2010 )

. Nonetheless, until more data becomes available, the use of type curves at least for aggregate qualitative analysis is not unreas onable. UR estimates based on the type curve method for the 2010 vintage of horizontal wells in the major U.S. shale plays are given in Table A 2 . These URs were calculated assuming both a 30

- year well production lifetime, and a more conservative 15

- year we ll lifetime. A 30

- year well producing lifetime is widely assumed, particularly by the industry, when estimating shale well UR.

Table A2. Projected horizontal well URs for the major U.S. shale plays based on 2010 well IP rate data assuming 30

- year and 15

- y ear production lifetimes ( Source: Authors’ calculations based on HPDI 2012 ).

Estimated UR: 1x10 6 m 3 (30/15 year estimates) Shale Play Mean P80 P50 P20

Barnett 70.8 / 50.9 99.1 / 73.6 59.4 / 45.3 36.8 / 25.5 Fayetteville 76.4 / 56.6 104.7 / 76.4 73.6 / 53.8 45.5 / 31.1 Haynesville 150.0 / 118.9 192.4 / 155.7 141.5 / 113.2 96.2 / 76.4

Woodford 124.5 / 93.4 175.5 / 130.2 107.5 / 79.2 59.4 / 42.45

Marcellus 104.7 / 76.4 147.2 / 107.6 87.7 / 65.1 50.9 / 36.8

A 3. GHG INTENSITY OF FLO WBACK GAS HANDLING M E THODS
Knowing how gas produced during flowback is handled is necessary to evaluate the actual fugitive emissions from shale well hydraulic fracturing operations. Broadly speaking, three handling options exists; the gas can be vented directly to the atmosph ere, it can be flared, or it can be captured and routed to a pipeline. This final process is often referred to as “reduced emissions completion” or “green completion.” Of the three methods, venting has the highest GHG intensity, with every 1 m 3 of gas vent ed resulting in 0.788 m 3 of methane emissions ( EPA,6

2010 ). Flaring, when executed correctly is 98% efficient, thus resulting in 0.01

– 0.02 m 3 of methane emissions per m 3 of natural gas flared ( EPA, 2010 ). Gas capture have the potential to completely elimina te any methane or CO 2 emissions resulting from flowback; however, in practice this is probably not achievable. Data from the EPA suggests that green completions result in the capture of at least 90% of potential methane emissions ( EPA, 2010 ). This is likel y an underestimation of the gas captured during well

- executed green completions; however, we use it for analysis purposes in this paper. The specific GHG emissions factors of the three gas handling techniques are given in Table
A 3 . These factors were calcu lated assuming natural gas is composed of 78.8% methane by volume ( EPA, 2010 ). The GHG impact of other constituent gases was ignored. This is a clear simplification particularly considering natural gas often contains some volumes of CO 2 ; however, it is con sistent with the EPA’s own methodology and that used by others carrying out similar analysis ( Hultman et al. , 2011 ). The methane contribution was converted into CO 2 e using
both 100

- and 20

- year methane global warming potentials (GWPs) of 25 and 72 respectiv ely ( Solomon et al. , 2007 ). Calculations using both the standard 100

- year GWP and the 20

- year GWP are shown in order to acknowledge the debate currently occurring regarding which factor should be used when assessing the GHG emissions impacts of natural gas production and use ( Howarth et al. , 2011a; Howarth et al. , 2011b, Cathles et al. , in press ). A concise summary of the underlying scientific analysis that is cited as part of this debate is provided by Hultman ( Hultmen
et al. , 2011 ) and concludes that ther e exists, reasonable alternative perspectives on the issue. The specific emis sion factors reported in Table A 3 reveal the very dramatic impact that assumptions regarding how gas produced during flowback is handled can have on the analysis of GHG footprints . When assuming a 100

- year GWP for methane, the difference in the emission factors
of cold

- venting and green completions is an order of magnitude. Assuming a 20

- year GWP, flaring becomes the least GHG intensive method of handling flowback gas.

Table A 3. C alculation of emission factors for gas handling techniques, which can be deployed during shale well flowback operations assuming both 100 and 20

- year global warming potentials (GWP) (Source: Authors’ calculations).
Venting Flaring Gas Capture

CH 4 emitted : kg/1x10 3 m 3 of NG 537.5 10.8 53.8

CO 2 emitted: kg/1x10 3 m 3 of NG – 1,445.1

– Total emissions factor (100

- yr GWP): kg CO 2 e/1x10 3 m 3 of NG 13,438 1,714 1,344

Total emissions factor (20

- yr GWP): kg CO 2 e/1x10 3 m 3 of NG 38,701 2,219 3,870

To date, attemp ts to analyze the GHG intensity of shale gas production have relied heavily on information from the U.S. EPA. In particular, EPA analysis that suggests a natural gas emissions factor of 9,175 Mcf per unconventional well completion or workover is widely cit ed ( INGAA,7

2008 ). In this context the term “emissions factor” is misleading. The 9,175 Mcf figure is the EPA’s quantification of the volume of natural gas produced during flowback, i.e. the potential emissions, not the actual emissions. The authors suggest that the EPA revise their terminology in future publications and refer to this value as “potential emissions” in order to minimize confusion. As a quantification of “potential emissions” the 9,175 Mcf, or 259,836 m 3 of natural gas per completion appears r easonable, at least in qualitative terms. In comparison to the per

well potential emissions estimates in Table 1, the EPA figure is slightly lower than that for a 2010 mean performance well in the Barnett shale. This would be expected as the EPA figure is derived from data that included not just shale wells, but also lower performance unconventional
wells. The EPA is opaque with regards to defining how potential emissions are handled. This is understandable due to the lack of hard data; however, the agency does attempt to provide some directional guidance. For the purposes of estimating emissions from 2007 U.S. gas well completions and workovers, it assumes that 51% of the gas produced during well flowback is flared and 49% is vented ( EPA, 2010 ). This breakd own is based upon regulation in place in four sample states; Texas, New Mexico, Oklahoma and Wyoming. A 2008 INGAA report ( INGAA,
2008 ) estimated that if a more representative set of states were considered, then the proportion of flowback gas that would re quire flaring by regula tion would fall from 51% to 15% . However, regulation is only part of the gas

- handling picture. This is illustrated by the fact that in those states without a mandatory flaring requirement in the EPA’s four state analysis, ~70% of the gas produced during flowback was not vented, but in fact captured by green completion operations ( EPA, 2011 ). Additionally, an unknown, but likely similar proportion of the gas produced where flaring was required (as a minimum control) is also likely to h ave been captured. The reason for this is economic incentive. Where capture is possible due to infrastructure availability, the marginal cost of the process itself is low and operators generate value by doing it. A detailed discussion of green completion e conomics will be presented in section A 4.
The contention that real

- world flowback gas handling practices differ appreciably from what regulation alone demands is supported by the results of a 2011 American Natural Gas Alliance (ANGA) survey ( Thompson et al

. , 2010 ) of field practice. This survey recorded the gas handling approaches used by 8 exploration and production companies across a representative set of U.S. unconventional gas (both shale and tight sands) plays. A total of 1,578 wells were included in t he survey. Of these wells, gas was captured during flowback from 1,475 or 93%, 56 wells were flared and 47 wells were vented. Of course the fact that these results are the product of an industry sponsored survey means they are open to question, however, th e survey does represent the only large

- scale publically reported assessment of current gas handling field practice available. In preparing this paper the authors had extensive discussions with industry, EPA and other relevant groups regarding actual field practice. We have concluded that a reasonable representation of contemporary flowback gas handling field practice in U.S. shale plays would comprise 70% of wells using reduced emissions completions, 15% being flared and 15% being
vented (EPA, 2012b).8

Table A4. Specific GHG intensities for fi ve flowback gas handling scenarios assuming 100 year and 20 Year CH 4 global warming potentials (GWP) (Source: Authors’ calculations).

Flowback GHG intensity: kg CO 2 e/m3 of NG 100

- Year GWP 20

- Year GWP

Scenario 1: 100% vented 13.44 38.70

Scenario 2: 15% fl ared, 85% vented 11.68 33.23 Scenario 3 51% flared, 49% vented 7.46 20.10 Scenario 4: 93% GC, 4% flared, 3% vented 1.72 4.85

Scenario 5

— “Current Field Practice”: 70% capture, 15% flared, 15% vented 3.21 8.85

To il lustrate how assumptions regarding gas handling impact on the GHG intensity of shale

gas

- related hydraulic fracturing we take the potential emissions data from Tables 1 & 2, and calculate the associated actual emissions assuming five gas handling scenarios (Deutch, 2011); all potential emissions are vented as assumed in ( Howarth et al. , 2011a; Jacoby et al. , 2012), a case where 15% of gas is flared and the remainder is vented per ( INGAA, 2008; IEA, 2012), the regulatory case where 51% of gas is flared and the remainder is vented per EPA; (4) the ANGA survey case with 93% capture, 4% flared and 3% vented, and (5), a “current field practice” case, with 70% capture, 15 % flared and 15% vented. Table A 4 shows the GHG intensities in kg
CO 2 e/m 3 associated with eac h of the gas handling cases assuming both a 100

- year and 20

- year GWP factor for CH 4

Table A 5. Mean per

- well actual emissions fr om shale well hydraulic fracturing operations in 2010 (Source: Authors’ calculations based on HPDI 2012).

Barnett Fayetteville Haynesville Marcellus Woodford

Per

- well GHG intensity: Mg CO 2 e/well (100 y ea r CH 4 GWP)
100% v ented 3668.5 3977.6 15816.4 5442. 3 6544.2 15% flared, 85% vented 3188.4 3457.1 13746.5 4730.1 5687.8 51% flared, 49% vented 2036.2 2207.8 8778.8 3020.7 3632.4 ANGA Survey 469.9 509.5 2026.1 697.2 838.3 Current field p ractice 877.3 951.2 3782.2 1301.4 1564.9

Per

- well GHG intensity: Mg CO 2 e/well (20 y ea r CH 4 GWP)
100% v ented 10565.4 11455.5 45551.1 15673.9 18847.4 15% flared, 85% vented 9071.5 9835.7 39110.3 13457.6 16182.4 51% flared, 49% vented 5486.0 5948.2 23652.1 8138.6 9786.4 ANGA Survey 1323.8 1435.3 5707.3 1963.8 2361.5
Cur rent field p ractice 2415.3 2618.7 10413.0 3583.1 4308.5

The specific GHG intensities shown in Table A 4 reveal the importance of gas handling assumptions. There is 7.8X difference in intensity depending upon whether you assume al l potential emissions are vented (Scenario 1), or handled according to the ANGA survey (Scenario 4) assuming a 100 year CH 4 GWP. Coupling the specific GHG intensity factors in Table A 4 with the volumes of potential emissions from Tables 1 & 2 enables the e valuation of actual emissions9

associated with shale well flowback in 2010 for different gas handling scenarios. The per

- well
actual emissions are shown in Table A 5 , with the aggregate actual emissions in Table A 6

.

Table A 6. Total actual emissions from 2010 shale well hydraulic fracturing operations. (Source: Autho rs’ calculations based on HPDI, 2012)

Barnett Fayetteville Haynesville Marcellus Woodford To tal Total GHG intensity: Tg CO 2 e (100 y ea r CH 4 GWP)

100% v ented 6.5 3.5 8.1 3.1 1.4 23

15% flared, 85% vented 5.7 3.0 7.0 2.7 1.2 20

51% flared, 49% vented 3.6 1.9 4.5 1.7 0.8 13

ANGA Survey 0.8 0.4 1.0 0.4 0.2 3

Current field
p ractice 1.6 0.8 1.9 0. 7 0.3 5

Total GHG intensity: Tg CO 2 e (20 y ea r CH 4 GWP)

100% v ented 18.9 10.0 23.2 9.0 3.9 65

15% flared, 85% vented 16.2 8.6 19.9 7.8 3.4 56

51% flared, 49% vented 9.8 5.2 12.0 4.7 2.0 34

ANGA Survey 2.4 1.2 2.9 1.1 0.5 8

Current f i eld
p ractice 4.3 2 .3 5.3 2.1 0.9 15

A 4

. ECONOMIC MOTIVATION FOR FLOWBACK GAS CAP TURE IN SHALE PLAYS

As shown in Table A 4, the gas handling methods used to during flowback have a dramatic impact on the GHG intensity of the process. Because of the volumes of gas involved, pa rticularly in the case of contemporary shale wells, the extensive or exclusive use of venting would results in the process having a very high GHG intensity. By contrast, the extensive use of flaring and particularly capture result in much more benign emiss ion levels; however, both flaring and capture are not without their operation challenges. Capture in particular requires gas gathering facilities to be present at the well pad during flowback, something that is not always practical. Traditionally, gas expl oration and development involved an appreciable amount of trial and error or “wildcatting,” whereby single or small numbers of wells were drilled in a prospective area without a high level of certainty that those wells would ultimately prove to be commerci al. With this approach gas gathering systems would only be built after a well was completed. As a result capture was rarely practical or necessary for that matter as fracturing was less widely used. Contemporary shale gas development takes place in a very different manner. Often described as a “manufacturing process,” shale plays are developed in a relatively systematic manner made possible by the extensive and contiguous nature of the producing formations, and the relative assurance that any given well wil l produce gas. This relative a priori assurance regarding production coupled with the fact that multi

- well pads (often six or more well being drilled10

horizontally from one surface location) are now standard practice means that gathering
infrastructure is i n many cases being built in parallel or even ahead of actual well drilling and hydraulic fracturing operations. Operators in shale plays have a significantly higher economic incentive to have gathering facilities in place as wells are being completed than is the case in conventional plays. The assurance that the well will most likely produce gas means that by having gathering available as soon as a well is ready to go online saves the operators the carry costs associated with a completed but stranded well, and this boosts the present value of any given well. Furthermore, having gathering facilities in place also enables operators market the significant volumes of gas that will be produced during flowback. This is important as it means that producers are
fina ncially incentivized to minimize fugitive emissions. The current debate regarding the GHG intensity of flowback operations has relied heavily on assumptions regarding regulation. Considering regulation is of course necessary in any such analysis; however, it is not sufficient. To fully assess the situation, one must also consider the economics of the relevant gas handling techniques, as seen from the gas operators’ perspective. Both venting and flaring destroy value. Clearly though, if the present value of these approaches is higher (or less negative) than capturing the gas they will be chosen. For low performance unconventional tight sands wells it is certainly possible that the typical volumes of gas produced during flowback are too small to warrant gas c apture. However, in the case of contemporary shale wells the situation is entirely different. Table A 7 shows the mean per

- well and total value of gas produced during shale well flowback operations in 2010 assuming a conservatively low long

- term gas price o f $4.00/Mcf ($141.24 per thousand m 3 ) ( MIT, 2011 ).

Table A7. Gross value potential of gas produced during flowback operations in the major U.S. shale plays during 2010 (Source: Authors’ calculations).

Barnett Fayetteville Haynesville Marcellus Woodford Al l Plays

Per

- well value: $k 38.6 41.8 166.2 57.2 68.8

–
# of horizontal wells 1,785 870 509 576 208 3,948
Total value: $M 68.8 36.4 84.6 32.9 14.3 237.1

Overall, more than $237 million dollars

- worth of gas was produced during shale well flowback operat ions in 2010, or just over $60,000 of gas per well. These are significant cash flows and their importance to the overall economics of an individual well should not be overlooked, particularly as these cash flows occur in year 0 and so are not subject to an y time

value

- of

- money discounting. Of course gas capture is not free, and the costs must be included in the analysis. These authors define the cost of gas capture as the amortized capital cost along with operating costs, or more typically the rental costs of a green completion separator unit and accompanying crew. These units are in essence very high capacity versions of the multi

- phase separation systems that are permanently installed at producing well. They are specifically designed to handle the much hig her volumes of water and solids that flow during flowback and11

are typically skid or trailer mounted. The costs of gas gathering infrastructure are not considered in the assessment of the gas capture economics. These facilities are a sunk cost as they must be in place to get gas to market regardless of whether flowback gas captured, vented or flared. The cost of green completion services differs somewhat by play due to the different equipment specifications needed to handle differing levels of flowback. Devo n Energy reports a

per

- well per

- day cost of $1,000 for green completion services in the Barnett shale ( EPA, 2010 ). This figure is reasonable, and also representative of the costs in the Fayetteville shale. Correspondence with operators in the higher perfor mance plays such as the Marcellus shale have indicated that flowback gas capture costs of between $2,000 and $3,000 per

- well per

- day. To establish a conservative estimate of the value generation potential of gas capture, slightly higher

per

- well per

- day ca pture costs were assumed. $2,000 for the Barnett and Fayetteville shales, $3,000 for the Marcellus and Woodford plays and $6,000 for the very high volume wells in the Haynesville. Coupling these costs with the gross revenue figures from T able A 7 enables th e net value potential of green completions to be calculated. The resu lts of this are shown in Table A 8

.

Table A8. Net value potential of gas produced during flowback operations in the major U.S. shale plays during 2010 (Source: Authors ’ calculations).

Ba rnett Fayetteville Haynesville Marcellus Woodford All Plays

Per

- well gross revenue: $k $ 38.6 $ 41.8 $ 166.2 $ 57.2 $ 68.8

–

Per

- well capture cost: $k $ 18.0 $ 18.0 $ 54.0 $ 27.0 $ 27.0

–

Per

- well net value of
capture: 20.6 23.8 112.2 30.2 41.8

–

# of horizont al wells 1,785 870 509 576 208 3,948

Total net value potential of gas capture: $M $36.7 $20.7 $57.1 $17.4 $8.7 $140.6

The results in Table A 8 show that gas capture generates value in all plays. For an average well in most shale plays the net additional value will be anywhere from $20,000 to $40,000. In the Haynesville the net value per well of capture will be over $100,000. Given 2010 activity levels, the total net value of gas capture is just over $140 million. As discussed earlier, it is not practical to expect the use of green completion techniques on 100% of shale wells; however, assuming that 70% of shale wells are green completed, this still represents almost $100 million dollars in annual value generation as $4.00/Mcf gas. The preceding analysis of gas capture economic attractiveness makes a number of assumptions, albeit reasonable ones regarding the wellhead gas price and the cost of capture. Sensitivity analysis on these variables provides further insight. Figures 5 shows what percentage of the 20 10 Barnett well population would yield positive net revenue from gas capture assuming the cost of the completions was $1,000, $2,000 and $3,000 dollars per day for a 9 day flowback period, at $4.00/Mcf wellhead gas price.12

At the $1,000 per day green comple tion cost quoted by Devon Energy ( 21 ), 95% of wells generated positive net revenue, i.e. the value of the gas captured and sold was more than the cost of capture. At our more conservative $2,000 per day case 83% of all wells still generated positive

revenu e, and even assuming a very high cost of $3,000 per day, 64% of wells generated positive

net revenues. Figure A 6 shows the impact of varying gas price on the green completion economics of the same wells assuming a fixed completion cost of $2,000 per day.

Figure A5. Percentage of 2010 Barnett shale wells for which gas capture yields positive and negative net revenues assuming a wellhead gas price of $4.00/Mcf and gas capture costs of $1 ,000, $2,000 and $3,000 per day (Source: A uthors’ calculations).

Figure A6. Percentage of 2010 Barnett shale wells for which gas capture yields positive and negative net revenues assuming wellhead gas prices of $2.00/Mcf, $4.00/Mcf and $6.00/Mcf and a capture cost of $2,000 per day for a 9 day flowback period. (Source: Authors’ calculations)

. At $2.00/Mcf, 44% of the wells generate positive revenue, while at $6.00/Mcf, 92% of the wells were in the black. An important point to note is that although natural gas prices i n the U.S. during late 2011 and early 2012 have been between $2.50

– 3.00/Mcf range, these prices are not indicative of the likely long

- term equilibrium price in the U.S. market. The 2011 EIA Annual Energy Outlook ( U.S. EIA, 2011 ) projects wellhead gas price s of over the coming 5 year to be in the $4.00

– $4.50/Mcf range, while the 2011 MIT Future of Natural Gas study ( MIT, 2011 )

,13

projects gas prices over the same period to be in the $5.00

– $5.50/Mcf range. Given these projections, we feel that the use of a $4.0 0/Mcf assumption in the economic analysis of green completions is conservative.
The results of the sensitivities shown in Figures A5 and A6 reiterate the point that shale well flowback gas capture is economically attractive to operators. This is so for the vast majority of well even in lower performance shale plays like the Barnett, and even under higher than reasonable costs and lower than likely gas price scenarios.

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, ( http://www.anga.us/media/241575/anga axpc nsps neshap comments.pdf ). Baihly

, J

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, 135555.
Cathles, L., L. Brown, M. Taam, and A. Hunter, 2012: A commentary on “The greenhouse gas footprint of natural gas in shale formations” by R.W. Howarth, R. Santoro, and Anthony Ingraffea. Cli matic Change (in press). Curtis, M.E., C.H. Sondergeld, R.J. Ambrose, and C.S. Rai, 2012: Microstructural investigation of gas shales in two and three dimensions using nanometere

- scale resolution imaging. AAPG
Bulletin , 96(4): 665

– 677.
Deutch, J., 2011: T he good news about gas: the natural gas revolution and its consequences. Foreign Affairs

, 90 (1): 82

– 93. Devon, 2008: Devon Energy Barnett shale green completion initiative press release. ( http://www.dvn.com/CorpResp/initiatives/Pages/GreenCompletions.aspx ). Thompson, J. et al. Modeling well performance data from overpressured shale rese rvoirs. CSUG/SPE 137755 (2010).
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189. Modeling the Global Water Resource System in an Integrated Assessment Modeling Framework: IGSMWRS Strzepek et al. September 2010 190. Climatology and Trends in the Forcing of the Stratospheric Zonal-Mean Flow Monier and Weare January 2011 191. Climatology and Trends in the Forcing of the Stratospheric Ozone Transport Monier and Weare January 2011 192. The Impact of Border Carbon Adjustments under Alternative Producer Responses Winchester February
2011 193. What to Expect from Sectoral Trading: A U.S.-China Example Gavard et al. February 2011 194. General Equilibrium, Electricity Generation Technologies and the Cost of Carbon Abatement Lanz and Rausch February 2011 195. A Method for Calculating Reference Evapotranspiration on Daily Time Scales Farmer et al. February 2011 196. Health Damages from Air Pollution in China Matus et al. March 2011 197. The Prospects for Coal-to-Liquid Conversion: A General Equilibrium Analysis Chen et al. May 2011 198. The Impact of Climate Policy on U.S. Aviation Winchester et al. May 2011 199. Future Yield Growth: What Evidence from Historical
Data Gitiaux et al. May 2011 200. A Strategy for a Global Observing System for Verification of National Greenhouse Gas Emissions Prinn et al. June 2011 201. Russia’s Natural Gas Export Potential up to 2050 Paltsev July 2011 202. Distributional Impacts of Carbon Pricing: A General Equilibrium Approach with Micro-Data for Households Rausch et al. July 2011 203. Global Aerosol Health Impacts: Quantifying Uncertainties Selin et al. August 201 204. Implementation of a Cloud Radiative Adjustment Method to Change the Climate Sensitivity of CAM3 Sokolov and Monier September 2011 205. Quantifying the Likelihood of Regional Climate Change: A Hybridized Approach Schlosser et al. October
2011 206. Process Modeling of Global Soil Nitrous Oxide Emissions Saikawa et al. October 2011 207. The Influence of Shale Gas on U.S. Energy and Environmental Policy Jacoby et al. November 2011 208. Influence of Air Quality Model Resolution on Uncertainty Associated with Health Impacts Thompson and Selin December 2011 209. Characterization of Wind Power Resource in the United States and its Intermittency Gunturu and Schlosser December 2011 210. Potential Direct and Indirect Effects of Global Cellulosic Biofuel Production on Greenhouse Gas Fluxes from Future Land-use Change Kicklighter et al. March 2012 211. Emissions Pricing to Stabilize Global Climate Bosetti et al. March 2012 212. Effects of Nitrogen Limitation on Hydrological Processes in CLM4-CN Lee & Felzer March 2012 213. City-Size Distribution as a Function of Socio-economic Conditions: An Eclectic Approach to Down-scaling Global Population Nam & Reilly March 2012 214. CliCrop: a Crop Water-Stress and Irrigation Demand Model for an Integrated Global Assessment Modeling Approach Fant et al. April 2012 215. The Role of China in Mitigating Climate Change Paltsev et al. April 2012 216. Applying Engineering and Fleet Detail to Represent Passenger Vehicle Transport in a Computable General Equilibrium Model Karplus et al. April 2012 217. Combining a New Vehicle Fuel Economy Standard with a Cap-and-Trade Policy: Energy and Economic Impact in the United States Karplus et al. April 2012 218. Permafrost, Lakes, and Climate-Warming Methane Feedback: What is the Worst We Can Expect? Gao et al. May
2012 219. Valuing Climate Impacts in Integrated Assessment Models: The MIT IGSM Reilly et al. May 2012 220. Leakage from Sub-national Climate Initiatives: The Case of California Caron et al. May 2012 221. Green Growth and the Efficient Use of Natural Resources Reilly June 2012 222. Modeling Water Withdrawal and Consumption for Electricity Generation in the United States Strzepek et al.
June 2012 223. An Integrated Assessment Framework for Uncertainty Studies in Global and Regional Climate Change: The MIT
IGSM Monier et al. June 2012 224. Cap-and-Trade Climate Policies with Price-Regulated Industries: How Costly are Free Allowances? Lanz and Rausch July 2012. 225. Distributional and Efficiency Impacts of Clean and Renewable Energy Standards for Electricity Rausch and
Mowers July 2012. 226. The Economic, Energy, and GHG Emissions Impacts of Proposed 2017–2025 Vehicle Fuel Economy Standards in the United States Karplus and Paltsev July 2012 227. Impacts of Land-Use and Biofuels Policy on Climate: Temperature and Localized Impacts Hallgren et al. August
2012 228. Carbon Tax Revenue and the Budget Deficit: A Win-WinWin Solution? Sebastian Rausch and John Reilly August 2012 229. CLM-AG: An Agriculture Module for the Community Land Model version 3.5 Gueneau et al. September 2012 230. Quantifying Regional Economic Impacts of CO 2 Intensity Targets in China Zhang et al. September 2012 231. The Future Energy and GHG Emissions Impact of Alternative Personal Transportation Pathways in China Kishimoto et al. September 2012232. Will Economic Restructuring in China Reduce TradeEmbodied CO 2 Emissions? Qi et al. October 2012 233. Climate Co-benefits of Tighter SO 2 and NO

x Regulations in China Nam et al. October 2012 234. Shale Gas Production: Potential versus Actual GHG Emissions O’Sullivan and Paltsev November 2012