Abstract

Casing failure rate is high in steam injection wells and especially in cyclic steam injection wells. The high casing failure rate in such wells is related to the high casing temperature elevation from steam injection. Casing failures varies from casing ID restriction (including buckling and/or collapse) to casing parted (including leak and/or hole). This paper presents a modeling and analysis on casing temperature elevation, casing thermal stress/strain, and casing failure mechanisms in steam injection wells, with comparing with previous casing failure field-data from a Chevron steam injection project. It shows that high thermal axial compressive stress/strain can cause casing hot-yield and is attributed to casing ID restriction (including buckling and/or collapse), and high thermal axial compressive-tensile stress/strain alternation in cyclic steam injection can cause casing fatigue and is attributed to casing parted (including leak and/or hole).

Casing strain-based design seems needed for steam injection wells to take into consideration of casing hot-yield due to high thermal axial compressive stress/strain and casing thermal axial compressive-tensile stress/strain alternation on cyclic steam injection operation. Casing hot-yield and fatigue analysis approach presented in this paper may be used on casing strain-base design for steam injection wells to reduce casing failures, with selecting proper casing grade and weight to reduce casing hot-yield and casing fatigue.

Introduction

Chevron operates in many heavy-oil fields worldwide, and production casing failure is a concern on steam injection operations in these fields. This paper presents modeling and analysis on casing temperature, thermal stress/strain, and casing failure mechanism in steam injection wells, and compares with previous casing failure data from Chevron's Bakersfield Cymric 1Y steam injection project. Recommendations on casing design in steam injection wells are made, which have been used in Chevron's steam injection projects with good results.

Figure 1 shows the number of cumulative casing failure wells vs. the number of total wells in Cymric 1Y steam injection project from 1992 (the starting of Cymric 1Y project) to 2002, where the casing failure rate was about 19%, with casing failures being occurred in 69 wells out of total 370 wells completed and operated in that period.

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