Identifier

etd-04192012-102434

Degree

Master of Science in Petroleum Engineering (MSPE)

Department

Petroleum Engineering

Document Type

Thesis

Abstract

Sustained casing pressure (SCP) is considered a well integrity problem. The approach of this study is to look at SCP as environmental risk due hydrocarbon release. Currently, the risk is qualified by the value of surface pressure (Pcsg) that may cause failure of casing head. However, the resulting rate of gas emission to the atmosphere is not considered. Also not considered is a possibility of breaching the casing shoe due transmission of Pcsg downhole. The objective of this study is to develop methods for maximum possible air emission rates (MER) and risk of subsurface well integrity failure due SCP. Mathematical models and software are developed for computing MER, casing shoe strength (CSS) determined by leak-off test (LOT), and casing shoe pressure load resulting from SCP (SCPd). The models are used to find controlling parameters, identify the best and least-desirable scenarios, and assess environmental risk. It is concluded that emission potential of SCP wells with high wellhead pressure (Pcsg) can be quite small. The CSS model study reveals the importance of data recorded from LOT; particularly the time after circulation was stopped – the non-circulation time (∆ts). Ignoring ∆ts would result in underestimation of the ultimate CSS. The error is caused by the cumulative effect of thermally induced rock stresses, which strongly depend on ∆ts. The study displayed SCPd being controlled by the annular fluid properties which are subject to change in long time through mud aging; and mostly being overestimated. Comparison of surface versus subsurface failure scenarios yielded cases where the casing shoe demonstrates more restrictive failure criterion (CSS) than the burst rating of wellhead (MAWOP). Risk of casing shoe breaching (RK) is quantified using the CSS and SCPd models and application of risk analysis technique (QRA). The CSS distribution followed log-normal trend due the effect of ∆ts, while the SCPd distribution maybe of various shapes dependent on the annular fluid size and properties that are not well known. Possible scenarios of casing shoe breaching are statistically tested as a hypothesis of two means. The study produced engrossingly variant outcomes, RK changing from 1 to 80 percent.

Date

2012

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Wojtanowicz, Andrew K.

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