Design and Surveillance Tools Help Lower Integrity Risks for High-Temperature Wells

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 184159, “Use of Technical Design and Surveillance Tools To Minimize Operating Integrity Risk in High-Temperature Wells,” by Mirko Zatka, SPE, Shell Canada Energy, prepared for the 2016 SPE International Heavy Oil Conference and Exhibition, Mangaf, Kuwait, 6–8 December. The paper has not been peer reviewed. Thermal-well operations come with significant additional complexity in regard to maintaining wellbore integrity and hydraulic isolation from other formations. This is because of the extreme loads that may be placed on the well casing and liners, caused by the wide set of operating temperatures and pressures the wellbores may experience. To ensure that the wellbores can fulfill their anticipated operating need safely, careful design of the casing, liners, connections, and cement during the project-development phase is an absolute requirement. Background Wells designed for heavy-oil thermal-recovery projects will be exposed to a potentially wide range of operating temperatures. These can exceed 340°C for the deepest heavy-oil-bearing formations and can be as low as 5°C during well workovers. Such a range of operating conditions will cause the casing to yield under compressive conditions, and most likely under tensile conditions also, as it undergoes thermal cycling from the heating and cooling requirements of well operations. A thermal cycle is defined here as the confined casing material being heated to the point that it yields and plastically deforms under a compressive load, followed at some later time by sufficient cooling to force it to yield and plastically deform under a tensile load. This is an operating requirement for which casing and liners are not normally designed in conventional applications but is frequently unavoidable in thermal operations. As a result, consideration of material properties of the tubulars requires a much deeper understanding of the chemistry, manufacturing, and heat-treating processes in order to select the optimal material. Similarly, casing connections play a key role in well integrity, based on their ability to withstand stress cycles in the casing or liner string. Casing-cement composition and placement procedures are also key design parameters because thermal cycling of the casing will expose the cement to very large stresses across the metal/cement bond and potentially can alter the cement properties themselves. In turn, the operating practices applied to wellbores and the operating envelopes used to determine safe limits become keys to long-term integrity and safety.

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