Investigations on the surface well cement integrity induced by thermal cycles considering an improved overall transfer coefficient

Abstract

Wellbore cement is used as a mechanical and hydraulic barrier in order to support casing and to prevent vertical and horizontal fluid migration, making wellbore cementing jobs one of the most important operations in thermal recovery projects. Drilling high quality wells requires the use of high-performance drilling muds that can support and protect the wellbore during the drilling process. Drilling mud will create an internal and external filter cake to protect the well during drilling. Although the external filter cake is usually removed before or during cementing jobs, the internal filter cake remains in the near-wellbore formation throughout the life of the well. This directly influences the wellbore overall heat transfer coefficient. As thermal well design relies on maximizing the heat delivered to the reservoir, minimizing heat losses to top formations while also protecting casing and cement layers is mandatory.This paper presents a unique experimental investigation of thermal cycle behavior of cement with focus on surface casing cementing. A more accurate assessment of overall heat transfer coefficients, directing efforts towards increasing the efficiency and understanding of thermal well design has been also performed in order to better understand the induced thermal loads on cements under complex scenarios. Thermal mixing laws have been used to determine the approximate impact of drilling fluid invasion and filter cake formation within rocks’ pores on overall heat transfer coefficients. In an experimental approach it was noticed that applying temperature cycles to fresh cements (curing time less than 21 days) will lead to mechanical strengthening of the casing-cement-system, enhancing well integrity, whereas old cemented wells will lose strength.