Environmental Risk Arising From Well-Construction Failure--Differences Between Barrier and Well Failure, and Estimates of Failure Frequency Across Common Well Types, Locations, and Well Age
- George E. King (Apache Corporation) | Daniel E. King (WG Consulting Group)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Operations
- Publication Date
- November 2013
- Document Type
- Journal Paper
- 323 - 344
- 2013. Society of Petroleum Engineers
- 6.5 Environment, 2 Well Completion,
- 6 in the last 30 days
- 1,478 since 2007
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Do oil and gas wells leak to the environment? This paper will show the greatmajority of wells do not pollute. The purpose of this paper is to explain basicconcepts of well construction and illustrate differences between single-barrierfailure in multiple-barrier well design and outright well-integrity failurethat could lead to pollution by use of published investigations and reviewsfrom data sets of more than 600,000 wells worldwide. For US wells, whileindividual-barrier failures (containment maintained and no pollution indicated)in a specific well group may range from very low to several percent (dependingon geographical area, operator, era, well type, and maintenance quality),actual well-integrity failures are very rare. Well-integrity failure occurswhen all barriers fail and a leak is possible. True well-integrity failurerates are two to three orders of magnitude lower than single-barrier-failurerates.
When one of these rare total-well-integrity failures occurs, gas is the mostcommon fluid lost. Common final-barrier leak points are failed gaskets orvalves at the surface and are easily and quickly repaired. If the failure is inthe subsurface, an outward leak is uncommon because of lower pressure gradientin the well than in outside formations. Subsurface leaks in oil and gas wellsare rare and routinely comprise exterior-formation salt water leaking into thewell toward the lower pressure in the well.
Failure frequencies are estimated for wells in several specific sets ofenvironmental conditions (i.e., location, geologic strata, produced-fluidcomposition, and soils). Estimate accuracy depends on a sufficient database ofwells with documented failures, divided into (1) barrier failures in amultiple-barrier system that did not create pollution, and (2) well-integrityfailures that created a leak path, whether or not pollution was created.Estimated failure-frequency comparisons are valid only for a specific set ofwells operating under the same conditions with similar design and constructionquality. Well age and construction era are important variables. There isabsolutely no universal definition for well-failure frequency.
|File Size||1 MB||Number of Pages||22|