Forecasting Significant Incidents in Gas Fields
Test Case: Barnett Shale, Fort Worth, Texas
byJerry Lobdill, physicist and Ch. E.
(ret.)
One Picture is Worth...
Significant Incidents (SI) A US DOT term meaning an incident
involving any of: $50,000 in damage or more Fire Explosion Injury Death
The RRC collects mandatory reports of SI’s for the US DOT
Purpose of Study Use Significant Incident historical
data to quantify the risk associated with urban gas drilling and production.
Apply findings to the City of Fort Worth (Barnett Shale)
Barnett Shale Gas Well Density 2007
Proposed Statistic Average Significant Incident Rate
per 1000 gas wells per unit time. This is scalable to a field of any
size.
History of Barnett Shale Play Play covers about 15 counties First wells drilled in the northern
rural region in the 1990s By June 2008 there were 7766 wells First wells in Fort Worth area drilled
in 2001 As of last week 2008 a total of 1376
well permits had been issued in FW
Factors Affecting SI Rate No. producing wells Miles of gathering pipeline Population density Regulation Maintenance/Inspection Age of Field
Population Density vs SI Rate Certain kinds of human activity
increase the SI Rate above that experienced in rural settings.
The historical SI data available are mostly for non-urban areas.
Fort Worth has 2333 people/sq. mi. Our forecasts will be conservative.
The Effect of Regulation on SI Rate Regulations do not imply safety. They are the result of a tug of war
between profit and safety. Profit interests are strongest. Regulations are only as good as the
enforcement budget. Use modern TX RRC
Regulation/enforcement in this study.
Effect of Maintenance/Inspection, Age Regular inspection should
minimize SIs. Inspection without corrective
maintenance will not prevent SIs. As gas field ages maintenance and
inspection receive short shrift. Our forecasts will be conservative.
Wells and Pipelines in and Near Tarrant County, 2007
Analysis Summary There were 9 SI’s from 2004-2007
in the Barnett Shale. Statistical analysis shows Fort
Worth will have (conservatively) a “significant incident” about every 6 months on average when full production is achieved (3000 wells).
The Barnett Shale Data
Number of Incidents vs Number of Wells
Barnett Shale Incidents, 2004-2007
y = 5.45066E-04x + 4.47961E-01
R2 = 6.32528E-01
0
1
2
3
4
5
0 1000 2000 3000 4000 5000 6000 7000
No. Wells
Nu
mb
er o
f In
cid
ents
/ ye
ar
Mathematically Assuming only that the SIs are independent
events... The probability that there are exactly k SIs in a
period of t months when the average rate is SIs per month is given by the Poisson distribution.
The equation is
Simulated Timeline, 3000 Wells—One Replication
Maximum time between Significant Incidents for this replication is about 17.6 months.
Event Timeline, Poisson Process, Average rate =1/6
0
1
0 12 24 36 48 60 72 84 96 108 120 132 144 156
Number of months
SI Rate Implications for Fort Worth Property insurance against gas
damage will be mandatory. Home values will go down (for
sales, but not for taxes) PITI will escalate. Population will decrease. Taxes will go up. Bond ratings will decline.
In Fort Worth Today... High Impact drilling is routinely
permitted. For-profit gas companies are given
eminent domain power to seize private property for pipeline ROW.
City, State claim impotence.
Conclusions Drillers and their allies in local government
ignore the public safety aspects of shale bed gas drilling today.
The public cannot afford to accept this rosy view of life in an urban gas field.
As new shale bed field projects begin, citizens should use this analytical tool to forecast the SI rate and demand restriction of pipeline and drilling site locations to industrial zones.