Failure Analysis and Service Life Prediction of 80SH Casing Steel under Thermal Cycle Service Environment

Abstract

The main exploitation process of heavy oil is cyclic steam huff and puff. Cyclic operation causes cumulative damage to thermal recovery casing and causes a large number of failures. Failure analysis shows that the main failure factor of thermal recovery casing is the low cycle fatigue process caused by thermal cycle, which results in the decrease of strength of casing material, thus causing casing fracture and failure. Based on the failure analysis results, the low cycle fatigue tests of 80SH thermal recovery casing steel under different temperature, strain, pre-strain and other conditions were carried out. The influencing factors, life prediction model and criterion of service safety of casing materials under thermal recovery service conditions were first proposed, which provides a strong theoretical basis for the service safety design theory of thermal recovery casing materials. The research shows that the strain limit and low cycle fatigue life are the two core issues of service life. Life predictions need to satisfy two criteria. The first is the strain criterion. The strain limit should be lower than the total strain during the long service life. And the second is the low cycle fatigue criterion, which satisfies the expectation of low cycle fatigue life under double conditions of strain amplitude and mean strain.

Study on the Residual Strength of Nonlinear Fatigue-Damaged Pipeline Structures

“…Low-strength, soft metals tend to cyclic harden in low-cycle fatigue; however, high-strength metals generally tend to cyclic soften during low-cycle fatigue, resulting in continuous deterioration of material properties. The evolution of material properties during service plays a decisive role in the service safety of pipelines [2]. During the service of circulating steam huff and puff thermal recovery well casing, the casing material is under the service conditions of accumulated plastic deformation and strain fatigue, and necking and fracture failures often occur [3][4][5].…”

Effect of the Service Temperature on the Strength Plasticity and Fracture Mechanism of Cr-Mo Casing Steel

“…The unconventional oil and gas resources, such as ultra deep well, tight oil well and thermal recovery well, put forward higher requirements for the service performance of casing string [1,2]. Casing is the only channel connecting the underground oil-gas reservoir and the ground oil and gas production platform, and its safety plays a decisive role in the service life of the wellbore [3,4]. The service environment of unconventional oil and gas resources is complex, and the service temperature ranges from room temperature to 350 ℃.…”