Marcellus Shale in Pennsylvania: A 2,600 Well Study of Estimated Ultimate Recovery (EUR) 2015 Update

Transcription

1 Marcellus Shale in Pennsylvania: A 2,600 Well Study of Estimated Ultimate Recovery (EUR) 2015 Update Gary S. Swindell, P.E., Consulting Petroleum Engineer, Dallas, Texas Copyright 2015, Gary S. Swindell. Abstract The Marcellus Shale in Pennsylvania is a remarkable success story. From almost no production in 2008, more than 5,400 Marcellus wells were on line in June 2014 and more than 1,200 wells are being added each year. Monthly unconventional gas production in the state was more than 323 Bcf per month over the last six months ending in June 2014 and continues to increase. This study used the public reported production data for Marcellus wells in the state to make estimates of ultimate recovery (EUR) and to develop correlations between EUR and initial flow rate, horizontal length and the date of first production. Distributions of the EUR were developed for individual counties and regions. Finally, some normalized decline curves are presented. For 2,600 horizontal wells with enough history to forecast a decline profile, the estimated ultimate recovery averages 4.3 billion cubic feet equivalent (Bcfe) per well with a median of 3.6 Bcfe. The results vary considerably by region in six counties in the Northeast part of Pennsylvania, the average is 5.0 Bcfe per well and in Wyoming County the mean EUR is 8.9 Bcfe. In that Northeast region, there are a number of wells exceeding 15 Bcfe EUR. (Lease condensate was converted to an equivalent gas volume using a price ratio of 20 thousand cubic feet (Mcf) per barrel). Initial or maximum production rate from the horizontal wells has increased from approximately 43,000 Mcf/month per well in 2008 to 129,000 Mcf per month for the wells completed in The average EUR more than doubled from the 2008 wells to 4.2 Bcfe per well in the 2010 wells as horizontal length doubled, fracturing technology advanced and drilling activity focused on the most productive regions in the Northeast and far Southwest part of Pennsylvania. Across the whole state, the wells in the study show an average initial decline of 47 percent with an average hyperbolic b-factor of Introduction Pennsylvania is now capable of supplying the whole Northeastern U.S. with natural gas, all from unconventional wells. In 2012, the six states in New England (CT, MA, ME, NH, RI, VT) together with the six mid-atlantic states and the District of Columbia (DE, DC, MD, NJ, NY, PA) consumed 325 Bcf per month according to the Energy Information Administration. It is the result of the completion of some 5,400 wells in the Marcellus and other shale zones. As recently as 2007, Pennsylvania produced only nine-tenths of one percent of US natural gas. Now the state produces approximately 7.5% of the country s natural gas. Although the public data is limited there is now adequate production history to draw some early conclusions about the producing performance of a significant number of these wells. Fig. 1 shows the monthly gas production in Pennsylvania from Marcellus Shale wells, vintaged by the year of first production and labeled with the number of wells in each vintage. The earliest 2008 wells added relatively little volume compared to the later wells as the completion methods were refined and the areas of best productivity were identified.

2 2 Gary S. Swindell, Petroleum Engineering Marcellus Study 2015 Pennsylvania Marcellus Gas Production Vintaged by year of first production 350,000, ,000, ,000,000 By comparison, Texas gas well production is 510,000,000 MCF/month from 97,000 gas wells MCF per Month 200,000, ,000,000, Northeastern States consume 345,000,000 MCF per month ,000, Jan-08 Jan-09 Jan-10 Jan-11 Jan-12 Jan-13 Fig. 1 Total Pennsylvania Marcellus gas production. The Scope of the Study Individual monthly production history data through February, 2015 for the Marcellus wells were used for the study. Monthly is in quotes because prior to 2015 the publically available data collected by Pennsylvania s Department of Environmental Protection is reported in six month totals and is simply divided by the number of days in each month by the commercial data providers. As a result, the production data is coarse, but it is what is available for a broad study without access to private information. An approach using rate vs. time plots has weaknesses. The coarseness of the data often obscures the early monthly rates since the first report made is for a six month period even though the well may have been on line for fewer months. Also, there were known pipeline take-away problems in the Northeast and liquids processing difficulties in the Southeast. Quantifying these is impossible without much more detailed, private information. Nevertheless, for many of the wells a decline profile is established and sufficient for forecasting (see Fig. 9). Of the 4,600 wells for which production data was available, 2,647 had enough data and a sufficiently established decline profile to estimate the ultimate recovery using rate vs. time plots. The wells with the first production in 2013 or 2014 were excluded from the study since the limited data made projections more uncertain. A regional breakdown, dividing the state into six areas, Northeast, Northwest, West Central, Mountain, Green-Fayette, and Washington, was made to analyze well performance in a more local way. (Fig. 21 in the appendix shows the location of the wells in the study and the regional divisions.) In addition, the Pennsylvania Department of Conservation and Natural Resources maintains a database of well information called PA*IRIS/WIS. The IRIS system contains only document images while the Well Information System (WIS) holds digital data. It contains flow test and perforation data among other things, captured from the Form 5500 Well Record and Completion Report. (Unfortunately, the database does not capture all the information on Form 5500 fracturing data for instance.) The flow and depth data was used to develop some correlations discussed below. Finally, groups of individual well production data were normalized, bringing all monthly production back to the same starting date in order to produce average decline profiles for regions and time periods. Conversion of oil and lease condensate was done using a price ratio of 20 Mcf per barrel. Natural gas liquids (NGL) yield was not taken into account as the data is not available publically.

3 Gary S. Swindell, Petroleum Engineering Marcellus Study Changes over Time Initial monthly (or maximum) production rates have increased since the first drilling in 2008 (Fig. 2), almost tripling as completion techniques were refined and better shale areas were defined. But the trend of increasing rates has flattened since Fig. 2 Initial production rate by year of first production. The increase in initial production rate during the early years of the Marcellus development may be related to an increase in the horizontal length during the same period. For a subset of 1834 wells where an estimate of the horizontal length was able to be made, the average horizontal section increased from 2,280 ft in 2008; 2,890 ft. in 2009; 3,800 ft in 2010; 4,100 ft in 2011; and 4,500 ft in the 2012 wells. Average decline profiles for the whole state, vintaged by the year of first production are summarized in Table 1. Vintage Average initial production Mcf/month Average initial decline rate % Hyp b factor Average EUR Statewide - Bcfe , , , , , Table 1. Average decline profiles for the Pennsylvania Marcellus. EUR also increased during that period. But the range of results remained wide even in the prolific Northeast region. Fig. 3 shows the individual well EUR vs. the date of first production, color coded by county for just the Northeast region (other regions are in the appendix). The increase appears to have slowed or ended by the end of 2010, possibly the result of expanding the drilling activity into areas where the Marcellus Shale was not as prolific.

4 4 Gary S. Swindell, Petroleum Engineering Marcellus Study 2015 Fig. 3 EUR vs. the date of first production. Estimated Ultimate Recovery Summary For the 2,648 wells included in the study, the estimated ultimate recovery projected from the rate vs. time plots is summarized by county in Table 2. The best average EUR is in Wyoming County although there were only 51 wells in the study there. The Sullivan county average is second best but the group has only seven wells. Of the large well-count counties, Susquehanna and Bradford stand out, along with Lycoming and Greene. Lycoming County is an example of high variation in EUR for which the standard deviation of the LN(EUR) is approximately 1.8 Bcfe out of a mean EUR of 4.03 Bcfe Number of Study wells County GAS EUR - Bcfe Est. Hz length - ft. Avg Gas Flow test - MCFPD Avg. Max Gas Production - MCF/month Average Initial decline rate Average Hyperbolic factor 11 ALLEGHENY ,487 2, , ARMSTRONG ,817 5,904 76, BEAVER , BLAIR ,764 41, BRADFORD ,600 8, , BUTLER ,731 1,690 59, CAMERON ,042 13, CENTRE ,918 3,029 42, CLARION ,724 2,099 32, CLEARFIELD ,871 3,122 47, CLINTON ,963 3,911 94, ELK ,939 2,315 48, FAYETTE ,981 2,463 72, FOREST ,057 17, GREENE ,491 7, ,

5 Gary S. Swindell, Petroleum Engineering Marcellus Study HUNTINGDON ,407 1,000 14, INDIANA ,800 3,758 52, JEFFERSON ,411 2,088 78, LYCOMING ,405 5, , MC KEAN ,651 1,707 56, POTTER ,993 50, SOMERSET ,106 1,304 43, SULLIVAN , SUSQUEHANNA ,971 8, , TIOGA ,214 5,467 88, VENANGO ,332 15, WASHINGTON ,219 3,762 75, WESTMORELAND ,013 4, , WYOMING ,714 15, , Table 2 - Summary of EUR by county. The distribution of EUR for the whole state is shown in Fig. 4. The regional summaries at the end of the paper (Figs. 11 through 22) will likely be more useful since this chart covers a wide variance in well performance across the state. Of particular note is the higher end of the distribution where there are 160 wells with a projected EUR in excess of 10 Bcfe, nearly all of which are in the Northeast region, mostly in Bradford, Susquehanna and Wyoming counties, where the net Marcellus thickness is greater than 200 ft (Piotrowski & Harper 1979). Seven wells in the study have a projected EUR greater than 20 Bcfe. Fig. 4 Distribution of Marcellus EUR for the entire state. The cumulative frequency line references the right axis. The distribution is log-normal, and most of the regional breakdowns can be converted to a normal distributions by plotting the logarithm of EUR. The exceptions are two low well count regions West Central and the Northwest where the EUR distribution is almost normal.

6 6 Gary S. Swindell, Petroleum Engineering Marcellus Study 2015 Some Correlations to the PA system data Although it is available as a subscription, the PA*IRIS /Well Information System (WIS) database can also be accessed in the Pennsylvania Geological Survey s office in Pittsburgh or by way of a data retrieval fee. Unfortunately, horizontal length is not included in the WIS system as a data item. Although the plats in the IRIS document image system often show the horizontal length for the drilling permit, it would be tedious to extract this for 2,000-plus wells. But for more than 2,100 wells, the database had total depth and perforation data. This data was used to generate an estimate of horizontal length by subtracting the uppermost perforation from either the total depth or the bottom perforation, whichever was greater. Average estimated horizontal length increased from 2,280 ft. for the 2008 vintage wells to more than 4,500 ft in the 2012 wells. The correlation of EUR to the estimated horizontal length for the two counties, Susquehanna and Tioga in the Northeast region, is shown in Fig. 5. Although there is a general increase in EUR with horizontal length, the correlation is not well defined, especially with laterals greater than 5,000 ft. And Fig. 6 shows the correlation of initial rate and the proxy for horizontal length. Fig. 5 EUR vs. estimated horizontal length Susquehanna and Tioga Co. Fig. 6 - Correlation between initial monthly production and the proxy for horizontal length.

7 Gary S. Swindell, Petroleum Engineering Marcellus Study For 678 of the wells included in the study there was after-treatment flow test data available from the WIS database which enabled a comparison between test rates and the actual production reported to the state. Since most of the wells do not begin producing on one of the state s six month reporting periods, an estimate had to be made of the initial production rate. A plot of the peak estimated production rates to the flow test rate reported on Form 5500 indicates that the actual production is approximately 60% of the flow test rates (Fig. 23 in the Appendix). Normalized Rate vs. Time Plots Normalizing of the rate vs. time curves by averaging the decline profiles of many wells back to the same starting date provides a view of how an average well is performing. It has the advantage of presenting an overall look at well performance that is uninterpreted. It carries disadvantages too, among which are problems with the early rates in which well production is increasing and not yet declining, pipeline and market restrictions, multiple well records and survivor bias (where the best wells last the longest and as a result have more effect on the tail end of the plot). And, the former six month Pennsylvania reporting interval suppresses some useful information. Figs. 7 and 8 show normalized plots for two groups of wells, the Northeast region and West Central Region API Cum Gas 3,593,917 mcf Cum Oil 0 bbl Ult Gas 3,593,917 mcf Ult oil 0 bbl 1 Mil NORMALIZED 1525 NORTHEAST REGION WELLS ( ) CO, BRADFORD, LYCOMING, SULLIVAN, SUSQUEHANNA, TIOGA, WYOMING COUNTIES NORMALIZED GAS PRODUCTION Monthly Rate 10,000 NUMBER OF ACTIVE WELLS IN GROUP 1, Time Fig. 7 Normalized decline for 1525 Northeast region wells

8 8 Gary S. Swindell, Petroleum Engineering Marcellus Study API Cum Gas 1,849,543 mcf Cum Oil 117 bbl Ult Gas 1,849,543 mcf Ult oil 140 bbl NORMALIZED 191 WEST CENTRAL REGION WELLS ( ) CO, NORMALIZED GAS PRODUCTION ALLEGHENY, ARMSTRONG, BEAVER, BUTLER, CLARION, INDIANA, JEFFERSON, WESTMORELAND 10,000 Monthly Rate 1,000 NUMBER OF ACTIVE WELLS IN GROUP Time Fig. 8 Normalized decline for 191 West Central region wells. Fig. 9 shows normalized declines grouped by the year of first production or vintage. The y-axis is linear. The improvement from the early 2008 and 2009 wells is striking, but the wells drilled since 2010 have remarkably similar decline profiles. Fig. 9 - Normalized rate vs. time by well vintage (linear).

9 Gary S. Swindell, Petroleum Engineering Marcellus Study Economic Assumptions Interests: Gas price: Oil/Lease condensate price: Operating cost: Bcf equivalent conversion: 100% working interest, 80% net revenue interest $3.25/MMbtu held constant $60/BBL held constant $3,000/month/well 20 Mcf per barrel price ratio Evaluation history Three studies have been done on the Marcellus wells using the same basic methodology: Evaluation date Wells in study Mean EUR Median EUR Conclusions December , Bcf 3.00 Bcf No conversion of oil / lease condensate to Bcf equiv. July , Bcf 3.03 Bcf No conversion of oil / lease condensate to Bcf equiv. July , Bcfe 3.60 Bcfe Conversion of oil / lease condensate to Bcf equiv. Estimated ultimate recovery for Pennsylvania s Marcellus horizontal wells using rate vs. time plots shows a statewide average of 4.3 Bcfe per well. There is a wide distribution between regions with most of the large wells in the Northeastern counties. An average decline profile for wells indicates an initial rate of 124,000 Mcf per month with an initial decline of 49% and a hyperbolic factor of.60. The decline profile is supported by both individual well declines and studies of normalized production for groups of wells. Acknowledgements Katherine Schmid, P.G., Senior Geologic Scientist at the Bureau of Topographic and Geologic Survey and the staff at the Pittsburgh office were most helpful with my access to the PA*IRIS/WIS database. References Piotrowski, R. G., and Harper, J. A., Devonian black shale and sandstone facies of the "Catskill" clastic wedge in the subsurface of western Pennsylvania. USDOE/METC, EGSP Series No. 13, 40 p., 39 maps, Morgantown, WV. Erenpreiss, M.S., Wickstrom, L.H., Perry, C.J., et al Organic Thickness Map of the "Marcellus". Modified from Harper and Kostelnik, 2011, Pennsylvania Geological Survey; Carter, K. 2008, Pennsylvania; Leone, J. New York; and Lewis, E. 2011, West Virginia. Pennsylvania Dept. of Conservation and Natural Resources: DNCR_ pdf. Wright, R., Marcellus/Utica Liquids Rich Gas Production Tempers Effects of Low Gas Prices. World Oil (June): Beckwith, R., The Marcellus Shale Gas Boom Evolves. J Pet Technol V. 65 Issue 06 (June): Ramkumar, J. and Rakesh, R Impact of Uncertainty in Estimation of Shale-Gas-Reservoir and Completion Properties on EUR Forecast and Optimal Development Planning: A Marcellus Case Study. SPE Res Eval & Eng V. 17 Issue 01 (January): SPE Marcellus activity continues apace EP Magazine, (April): Pennsylvania Topographic and Geologic Survey PA*IRIS/WIS public database.

10 10 Gary S. Swindell, Petroleum Engineering Marcellus Study 2015 Appendix Regional EUR distributions and normalized production plots Fig. 10 The wells and the regions used in the study.

11 Gary S. Swindell, Petroleum Engineering Marcellus Study NORTHEAST REGION Bradford, Lycoming, Sullivan, Susquehanna, Tioga, Wyoming counties Fig. 11 EUR distribution, Northeast Region API Cum Gas 3,593,917 mcf Cum Oil 0 bbl Ult Gas 3,593,917 mcf Ult oil 0 bbl 1 Mil NORMALIZED 1525 NORTHEAST REGION WELLS ( ) CO, BRADFORD, LYCOMING, SULLIVAN, SUSQUEHANNA, TIOGA, WYOMING COUNTIES NORMALIZED GAS PRODUCTION Monthly Rate 10,000 NUMBER OF ACTIVE WELLS IN GROUP 1, Time Fig. 12 Normalized decline of 1,525 wells in the Northeast Region.

12 12 Gary S. Swindell, Petroleum Engineering Marcellus Study 2015 NORTHWEST REGION Cameron, Elk, Forest, McKean and Potter counties Fig. 13 EUR distribution, Northwest Region API Cum Gas 1,075,440 mcf Cum Oil 29 bbl Ult Gas 1,075,440 mcf Ult oil 36 bbl NORMALIZED 77 NORTHWEST REGION WELLS ( ) CO, NORMALIZED GAS PRODUCTION CAMERON, ELK, FOREST, MCKEAN, AND POTTER COUNTIES 10,000 Monthly Rate 1, NUMBER OF ACTIVE WELLS IN GROUP Time Fig. 14 Normalized decline of 77 wells in the Northwest Region.

13 Gary S. Swindell, Petroleum Engineering Marcellus Study WEST CENTRAL REGION Allegheny, Armstrong, Beaver, Butler, Clarion, Indiana, Jefferson, Westmoreland counties Fig. 15 EUR distribution, West Central Region API Cum Gas 1,849,543 mcf Cum Oil 117 bbl Ult Gas 1,849,543 mcf Ult oil 140 bbl NORMALIZED 191 WEST CENTRAL REGION WELLS ( ) CO, NORMALIZED GAS PRODUCTION ALLEGHENY, ARMSTRONG, BEAVER, BUTLER, CLARION, INDIANA, JEFFERSON, WESTMORELAND 10,000 Monthly Rate 1,000 NUMBER OF ACTIVE WELLS IN GROUP Time Fig. 16 Normalized decline of 191 wells in the West Central Region.

14 14 Gary S. Swindell, Petroleum Engineering Marcellus Study 2015 GREEN-FAYETTE REGION Greene and Fayette counties Fig. 17 EUR distribution, Greene-Fayette Region API Cum Gas 2,576,797 mcf Cum Oil 10 bbl Ult Gas 2,576,797 mcf Ult oil 13 bbl NORMALIZED 300 GREEN-FAYETTE WELLS ( ) CO, NORMALIZED GAS PRODUCTION 10,000 Monthly Rate 1,000 NUMBER OF ACTIVE WELLS IN GROUP Time Fig. 18 Normalized decline of 300 wells in the Greene-Fayette Region.

15 Gary S. Swindell, Petroleum Engineering Marcellus Study WASHINGTON COUNTY Fig. 19 EUR distribution, Washington County API Cum Gas 2,017,402 mcf Cum Oil 18,063 bbl Ult Gas 2,017,402 mcf Ult oil 18,063 bbl NORMALIZED 447 WASHINGTON CO WELLS ( ) CO, NORMALIZED GAS PRODUCTION 10,000 Monthly Rate 1,000 NUMBER OF ACTIVE WELLS IN GROUP Time Fig. 20 Normalized decline of 447 wells in the Washington County. (Gas in red, cond. in green, well count in black).

16 16 Gary S. Swindell, Petroleum Engineering Marcellus Study 2015 MOUNTAIN REGION Blair, Centre, Clearfield, Clinton, Somerset counties Fig. 21 EUR distribution, Mountain Region API Cum Gas 1,400,963 mcf Cum Oil 0 bbl Ult Gas 1,400,963 mcf Ult oil 0 bbl NORMALIZED 107 MOUNTAIN REGION WELLS ( ) CO, NORMALIZED GAS PRODUCTION 10,000 BLAIR, CENTRE, CLEARFIELD, CLINTON, SOMERSET COUNTIES Monthly Rate 1, NUMBER OF ACTIVE WELLS IN GROUP Time Fig. 22 Normalized decline of 107 wells in the Mountain Region.

17 Gary S. Swindell, Petroleum Engineering Marcellus Study Actual Peak Production vs. Flow Test 1,000, ,000 Peak Estimated Production - MCF per Month 800, , , , , , ,000 y = x , , , , , , , ,000 1,000,000 Flow Test - MCF per Month Fig. 23 Flow test rates vs. peak estimated production reported to the state.