# Attachment B

Hydraulically Fractured Oil Wells

Joe Cardenas
XTO Energy, Inc.Answers to Charge Questions :

1. Please comment on the national estimates and per well estimates of methane and VOC emissions from hydraulically fractured oil well completions presented in this paper. Are there factors that influence emissions from hydraulically fractured oil well complet ions that were not discussed in this paper?

The national estimates of methane and VOC’s from hydraulically fractured oil wells do not seem to be reasonable or accurate for several reasons. First, the estimates used for all the major studies discussed are for uncontrolled emissions. While there are cases where emissions during the completion may be vented straight to the atmosphere, most events are controlled by
combustion . Combustion of hydrocarbons generally reduced emissions amounts by 95

- 98%. Second, t he national estimates gross up the uncontrolled amounts by the number of oil wells completed. However, th es e estimat es fail to take in to account the diverse nature of the many operating regions. The emissions data used by these studies are taken from a small selected number of regions. The regions selected tend to be higher pressure and thus have more emission. No consideration was given to lower emission areas thus driving the average emissions per well

up. At the very least, emissions should have bee n characterized as potential emissions instead of being represented as actual emissions. Authors of this paper should also have looked to the GHGRP for emissions estimates rather than coming up with estimates based on production volumes. While not require d, many operators have already been reporting emissions from hydraulically fractured oil wells and there is a sizeable dataset to analyze. Use of this data coupled with analysis of emissions controls already being used by industry would have resulted in

m uch lower emission estimates than what is provided in the report. Additional analysis of a larger sampling of reservoirs that included a broader range of associated gas volumes would also yield a lower potential emissions number than what is presented her e. There is no discussion or inclusion of areas where associated gas volumes are low.

2. Most available information on national and per well estimates of emissions is on uncontrolled emissions. What information is available for emissions, or what methods can be used to estimate net emissions from uncontrolled emissions data, at a national and/or at a per well
level?

It ’ s difficult to accept the premise of this question that assumes all emissions are uncontrolled. For reasons expressed in question 1, it is wro ng to make this assumption. The GHGRP is the best overall source of emissions data as more than 70 operators have been reporting emissions from the GHGRP for hydraulically fractured oil wells though not required. This is important data that has been over looked. “Available information” used by the authors is based on production data and makes several questionable assumptions of how to apply production volumes to determine flowback emissions. None of the assumptions used in the paper have been validated, a nd I would surmise they are wrong.Furthermore, the statement in the paper to justify rejection of GHGRP 

### : “The GHG Inventory estimates emissions from oil well completions, but does not distinguish between completions/recompletions of conventional wells an d completions/recompletions of hydraulically fractured wells” makes no sense and shows a basic misunderstanding of well completions. Conventional wells, ( vertical well bores ) , and unconventional wells (horizontal wellbores) can both be hydraulically fractured

. Given the report years of 2011 and 2012, the location of the wells being drilled, and the type of data being reported, it can easily be surmised that the wells in the dataset represent hydraulically fractured wells. Wells that are not hydraulic ally fractured would most likely not have associated gas emissions to report as there likely would be no flowback if there was no well stimulation.

3. Are further sources of information available on VOC or methane emissions from hydraulically
fractured oil we ll completions beyond those described in this paper?

As already mentioned another look at the GRHRP data is warranted. State programs may also have requirements to report these emissions for emissions inventories. An example is the Wyoming DEQ, complet ion emission reports are required to be filed on a per well basis. An example report can be found at http://www.shalegas.energy.gov/resources/071311_corra.pdf

4. Please comment on the various approaches to estimating completion emissions from hydraulically fractured oil wells in this paper.

• Is it appropriate to estimate average uncontrolled oil well completion emissions by using the annual average daily gas production during the first year and multiplying that value by the duration of the average flowback p eriod?

• Is it appropriate to estimate average uncontrolled oil well completion emissions using “Initial Gas Production,” as reported in DI Desktop and multiplying by the flowback period?

• Is it appropriate to estimate average uncontrolled oil well completi on emissions by increasing emissions linearly over the first nine days until the peak rate is reached (normally estimated using the production during the first month converted to a daily rate of production)?

• Is the use of a 3

- day or 7

- day flowback period f or hydraulically fractured oil wells appropriate?

a) It is not appropriate to use the average yearly gas production and multiply by the flowback period to estimate uncontrolled emissions. The flowback period will have different stages of flow from 100% stim ulation fluid to near flowline quality gas production . Because of the variations, using the yearly average would misrepresent the amount of emissions either high or low. b) Using “Initial Gas Production” is also not a good estimate since only the end period of the flowback gets close to initial production.c) It would not be appropriate to use a linear correlation for 9 days. No evidence suggests that maximum gas potential is reached in 9 days. d) The use of any average flowback days is not appropriate as all flowback will differ due to
circumstances.

5. Please discuss other methodologies or data sources that you believe would be appropriate for estimating hydraulically fractured oil well completion emissions.

See answer to question 2.

6. Please comment on the methodologies and data sources that you believe would be appropriate to estimate the rate of recompletions of hydraulically fractured oil wells. Can data on recompletions be used that does not differentiate between conventional oil we lls and hydraulically fractured oil wells be reasonably used to estimate this rate? For example, in the GHG Inventory, a workover rate of 6.5% is applied to all oil wells to estimate the number of workovers in a given year, and in the ERG/ECR analysis abov e a rate of 0.5% is developed based on both wells with and without hydraulic fracturing. Would these rates apply to hydraulically fractured oil wells? For hydraulically fractured gas wells, the GHG Inventory uses a refracture
rate of 1%. Would this rate be appropriate for hydraulically fractured oil wells?

The number of recompletions can be estimated by using the sub

- part W program to
obtain the number of workovers with hydraulic fracturing. Capture of data regarding the amount of uncontrolled emissions is more difficult since each region and reservoir will vary. Regional factors could provide estimates but expect each well to vary significantly. The rate of re

fracturing for oil wells is undetermined. I believe 1% may be too high.

7. Please comment on the fe asibility of the use of RECs or completion combustion devices during hydraulically fractured oil well completion operations. Please be specific to the types of wells where these technologies or processes are feasible. Some characteristics that should be

co nsidered in your comments are well pressure, gas content of flowback, gas to oil ratio (GOR) of the well, and access to infrastructure. If there are additional factors, please discuss those. For example, the Colorado Oil and Gas Conservation Commission req uired RECs only on “oil and gas wells where reservoir pressure, formation productivity and wellbore conditions are likely to enable the well to be capable of naturally flowing hydrocarbon gas in flammable or greater
concentrations at a stabilized rate in e xcess of five hundred (500) MCFD to the surface against an induced surface backpressure of five hundred (500) psig or sales line pressure, whichever is greater.”

RECs are implemented on the majority of oil well completions that have pressure. When enough g as is produced to operate a separator, the gas stream is sent to a combustion device. Consideration should be given to wells that do not have infrastructure to sell natural gas. These wells should be allowed to flare for an extended period (90 days) to all ow sale of liquid hydrocarbon. Low pressure exception should be allowed for wells whose pressure is below linepressure. A sufficient pressure differential is required to ensure flowback velocity is sufficiently high to adequately lift and clean out fluids and solids from hydraulic fracturing

. The Colorado rule seems appropriate for RECs as do the requirements of the Wyoming DEQ

.

8. Please comment on the costs for the use of RECs or com pletions combustion devices to control emissions from hydraulically fractu red oil well completions.

The cost of an REC will not substantially change the economics of the wells. Cost and equipment necessary will vary by well and region. There should be no substantive difference in cost than those for hydraulically fractured gas wells. Equipment requirements will essentially be
the same.

9. Please comment on the emission reductions that RECs and completion combustion devices achieve when used to control emissions from hydraulically fractured oil well completions.

It is typical for oil well completions which flow to use combustion devices. The devices typically reduce emissions by 95

- 98%. The EDF/UT study indicates a reduction of “ nearly 98% for the limited data being reported. Compared to the reported reductions for REC of about 98.8%, this is only a minimal difference of 1%. “

10. Please comment on the prevalence of the use of RECs or completion combustion devices during hydraulically fractured oil well completion and recompletion operations. Are you aware of any
data sources that wo uld enable estimating the prevalence of these technologies nationally?

See above. No studies that I am aware of , but fairly accurate inferences can be made by understanding general characteristics of the various reservoirs Wells completed in high pressur e reservoirs such as Bakken and Eagle Ford will most surely employ RECs or completion combustion devices, whereas low pressure formations such as those in East Texas or some areas of the Permian will not since the volume of associated gas is low to nonexis tent

.

11. Did the EPA correctly identify all the available technologies for reducing gas emissions from hydraulically fractured oil well completions or are there others?

EPA identified the current technologies. These technologies should be evaluated on a fit for purpose basis.

12. Please comment on estimates of associated gas emissions in this paper, and on other available information that would enable estimation of associated gas emissions from hydraulically
fractured oil wells at the national

- and the well

- lev el.

Because the term “associated gas emissions ” is used instead of “stranded gas emissions” it is easy to misinterpret the data set in Appendix A

. A reader can conclude from the data set that all hydraulically fractured oil wells in 2011 resulted in pro duced gas that was vented and not sold since the gas volumes in the data tables are labeled “associatedgas”. This is certainly untrue as many if not most of the wells in the data set actually do gather and sell the produc ed gas. Using the term “stranded gas” defined as a subset of associated gas that is produced gas in the production phase that is vented or flared
because it can’t be sold is recommended to avoid this misinterpretation.

The second problem with “associated gas emissions” is that the disc ussion in section 4.0 redefines the term as gas that is vented, not vented or flared as is provided in the definition in section 2.2. The focus of the discussion then is centered on how best to estimate uncontrolled emissions with no discussion of the importance in determining how many wells are vented versus flared. Consequently, the intent of this section is confusing since it is not known if EPA is only concerned with wells that vent associated gas or wells that both flare and vent associated gas. To get a true picture of stranded gas emissions, estimates of the use of controls is as important as estimating gas volumes themselves. I would posit that most high volume wells would be flared, whereas venting would be more prevalent with wells with low to no stranded gas volumes.

No real emission estimates seem to be provided in the paper other than to quote from a couple of sources such as Flare Up and the GHGRP. Other than that, discussion centers on possible methodologies to determine emissions. Att empting to develop an average GOR factor is not a feasible approach. It assumes its possible to have a direct correlation of oil production volume to gas volumes over the life of the well. This correlation doesn’t exist in oil and gas production. The go al is not clear, but If an average GOR factor is being considered for determining nationwide or regional emissions, the correlation is even worse and would be highly inaccurate. Additionally, oil wells with high gas volumes would skew such a factor such t hat it would misrepresent the many wells that produce little or no associated gas. There is no discussion of wells with low volumes of associated gas and is an important piece of missing information in the paper. The Permian Basin for example is an activ e area for hydraulic fracturing where there are many wells with little to no associated gas. Because volumes are so low, gathering for sales is uneconomic so associated gas is vented or flared but a nationwide factor skewed by wells in the Bakken or Eag le Ford would be an inaccurate representation for many Permian wells.

Volumes reported to state oil and gas agencies is another approach discussed, but shunned in the paper because there is no accounting for field gas used to support production such as instrument gas for pneumatics and fuel gas for fired sources such as heaters and compressor engines. However, volumes reported to oil and gas agencies is much more accurate than any attempt at using a one size fits all GOR. Additionally, field gas use would be only a very small percentage of the total volume of gas produced. Additionally, gas volumes reported are measured volumes not estimated, and I think in most states field use gas is not included in the rep orted volume since field use gas is an expense and royalties are not paid.13. Please comment on availability of pipeline infrastructure in hydraulically fractured oil formations. Do all tight oil plays (e.g., the Permian Basin and the Denver

- Julesberg Basin) have a similar lack of infrastructure that results in the flaring or venting of associated gas?

Pipeline availability differs by region and area within that specific region. Not all shale oil plays have infrastructure problems, and in many areas the iss ue of infrastructure is a decreasing problem as more gathering systems and processing facilities are constructed

.
Did the EPA correctly identify all the available technologies for reducing associated gas emissions from hydraulically fractured oil wells or are there others? Please comment on the costs of these technologies when used for controlling associated gas emissions from hydraulically fractured oil wells. Please comment on the emissions reductions achieved when these technologies are used for controll ing associated gas emissions from hydraulically fractured
oil wells.

The EPA did identify all the available technologies.

14. Are there ongoing or planned studies that will substantially improve the current understanding of VOC and methane emissions from hyd raulically fractured oil well completions and associated gas and available options for increased product recovery and emission reductions?

EDF/UT study attempts to further the on the ground measurements. Measurements taken by aircraft tend to be high and cannot differentiate between various sources.