Over the past decade, domestic energy production has been transformed by advance
ID: 112531 • Letter: O
Question
Over the past decade, domestic energy production has been transformed by advances in directional drilling and hydraulic fracturing, which made extracting oil and gas from tight shale formations economically viable. Development in the Fayetteville shale, a smaller natural gas-bearing formation in Arkansas, began in 2004. The figures below show A) cumulative natural gas production rates (in billions of cubic ft per day, Bcf/d) and B) a typical production decline curve for an individual well in the Fayetteville (in thousands of cubic ft per day, Mscf/d). Note: you can ignore the numbers listed in the figures as all relevant data are provided in each part of this problem.
a) Looking at the trends, which growth model (exponential or logistic) would you apply to cumulative natural gas production (i.e. the black line in Fig. A) and the decline profile for an individual well (Fig. B)?
b) Assume natural gas production (Fig. A) has leveled off at 2.8 Bcf/d following the peak in 2012. If natural gas production in 2006 averaged 0.5 Bcf/d, when the rate of increase was 2%, and reached 1.4 Bcf/d in 2009, what would have been the expected gas production rate (in Bcf/d) in 2011?
c) Production rates from oil and gas wells are highest when production starts and decline continuously over time. If the gas production rate from a Fayetteville shale well (Fig. B) is initially 2250 Mscf/d and falls to 1000 Mscf/d after 12 months, what was the monthlyrate of decline? Note: These units are how gas flows are typically reported in the industry (http://www.glossary.oilfield.slb.com/Terms/m/mscfd.aspx)
3.5 6000 2500 Peak December 2012 -Gas production .Number of wells 3 5000 First Year 57% Second Year 35% Third Year = 25% Fourth Year: 2096 2000 2.5 4000 1500 3000 down 2.2% 3-Year Decline 79% 1.5 2000 1000 1000 0.5 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 16 21 31 Months on Production 41 46 Figure 3-46. Fayetteville play shale gas production and number of producing wells, 2005 to 2014.72 Figure 3-47. Average decline protile for horizontal gas wells in the Fayetteville play.73 Decline profile is based on all shale gas wells drilled since 2009 Gas production data are provided on a raw gas basis.Explanation / Answer
a) For the figure A, it shows an exponential growth pattern whereas the figure B shown a logistic decline trend.
b) According to the given question and applying simple mathematics we can calculate the value for the expected gas production as,
In 2006 the production was 0.5 Bcf/day
In 2009 it was 1.4 Bcf/day.
so the difference in 3years = (1.4-0.5) Bcf/day = 0.9 Bcf/day
so it will be 0.3 Bcf/day in a year.
So from 2009 to 2011, it's 2year duration so it will increase by 2 Bcf/day showing a cumulative growth pattern.
c) In the beginning of the production well the gas flow was 2250 Mscf/d
whereas by the end of the year the flow rate was 1000 Mscf/d
So the change in the flow rate = (1000-2250) Mscf/d =-1250 Mscf/d
So the monthly rate of decline = -1250/12 Mscf/d = -104.16 Mscf/d.
Hence the decline will be of 104.16 Mscf/day.
d) The output of a well declines over time because there is less natural gas left in the well after some have been removed. With less amount of natural gas available, less will comes out over time. Moreover, the initial fractures may not be able to reach far enough to access all of the natural gas in the gas trapped areas, so the output may decline.
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