Casing Temperature and Stress Analysis in Steam-Injection Wells

Abstract

Abstract For steam injection parameters of greater than 700 psi and 500 deg F, a high production casing failure rate is often observed. This is due to severe thermal stress condition to the production casing string. The production casing may easily be in compression hot-yield under these conditions. This can lead to high casing failure risk in the forms of excessive deformation, buckling, and collapse. This paper presents an analysis on casing and cement stresses under the stated steam injection conditions. The interaction of casing-cement-formation is considered to help understand casing and cement failure mechanisms and potential approaches to reduce casing failures in cyclic steam frac wells. The loss of cement integrity and support to production casing string may occur under steam injection condition, which attributes to casing failures in the forms of excessive deformation, buckling, and collapse. Field surveyed temperature in a cyclic steam frac well is also presented and compared with modeled casing temperatures to show the needs of correctly modeling casing temperatures. Recent casing design practices in some Bakersfield area cyclic steam frac projects, including the successful use of high strength grade casing such as P-110, are discussed in order to reduce casing failures in the cyclic steam frac wells. Introduction In cyclic steam frac wells, high temperature steam (usually above 550 deg. F) is injected into the well though tubing to improve the heavy-oil recovery. For many years, casing failure rate has been high in these type wells. Although it is a commonly accepted casing design practice to assume cement integrity, cement is most likely failed in steam injection wells.1,2 Modeling cement stress becomes important to understand its failure risk, and to help improve casing design and reduce casing failures in wells with steam injection.