The quality of construction and maintenance of oil and gas wells has been called into question by media sources with reports of high rates of leakage and fears of pollution. This presentation looks at studies covering over 650,000 wells, primarily in but not limited to North America. Concepts of well construction are explained with emphasis on performance of properly constructed barriers within the well design in preventing leaks.
When examined in detail, most claims of leaks are found to be a single barrier failure within a multi-barrier system where a leak path is not formed. True well integrity failure rates (where a leak path is created) are two to three orders of magnitude lower than single barrier failure rates. Well integrity performance is shown to be related to several factors including best practice construction, era of well construction, type of well, changes in well operation, age of well and application of consistent, high quality maintenance.
Failure frequency numbers are estimated for wells in several specific sets of environmental conditions (location, geologic strata, produced fluid composition, soils, etc.). Accuracy of these numbers depends on a sufficient database of wells with documented failures, divided into: 1) barrier failures in a multiple barrier system that do not create pollution, and 2) well integrity failures that create a leak path, whether or not pollution is created. Estimated failure frequency is only valid for a specific set of wells operating under the same conditions with similar design and construction quality. Well integrity failures have generally decreased where learnings from an earlier era have been incorporated into new well designs. There is absolutely no one-size-fits-all well failure frequency.
George E. King is a registered professional engineer with 42 years industry experience with most aspects of completion, well construction and well failure analysis. He is Apache’s Distinguished Engineering Advisor.
He has written 67 papers, book chapters and articles. His work has focused on unconventional formations, sand control, perforating, fracturing and well construction risk analysis.
Degrees include a BS in Chemistry (Okla. State), BS in Chemical Engineering and Masters in Petroleum Engineering from University of Tulsa where he was also an Adjunct professor in completions engineering at night for eleven years.