Abstract
The sealing integrity of cement sheath in offshore wells is seriously threatened under high-temperature conditions, resulting in gas channeling and other problems. Given the lack of experimental results, in this study relevant samples of a cement slurry sealing section of a typical offshore high-temperature well have been prepared and analyzed. In particular, the mechanical properties have been assessed with a triaxial pressure servo instrument and a high-temperature curing kettle. The density and the Poisson’s ratio of the samples have also been tested. The stress-strain curve has been drawn to obtain the elastic modulus and the compressive strength. The rock brittleness index has been calculated according to the measured elastic modulus and the Poisson’s ratio, together with the brittleness and the compressibility of the cement samples. The test results show that the mechanical properties and bonding strength of the cement samples are optimal at 130°C, medium at 150°C, and poor at 180°C.
Highlights
Over the last few years, the exploration and development of offshore oil and gas has been increasing
When the compressive strength of the formation rock is greater than or equal to 40 MPa, the bond strength of the second interface with the cement sheath is excellent. According to this evaluation standard, the bonding strength quality of the second interface between the formation rock and the cement sheath can be evaluated based on the results of the core rock mechanics parameters obtained by the triaxial test
The simulated results show that the mechanical properties of the cement sheath at 130°C are better than 150°C and 180°C, which is mutually verified with the experimental results
Summary
Over the last few years, the exploration and development of offshore oil and gas has been increasing. The above research has discussed the related problems of mechanical properties of cement stones in detail, but the objects in the studies are mainly the cement sheath under normal temperature and pressure conditions. The mechanical properties of cement sheath under high-temperature conditions have been tested by using tuses triaxial pressure servo instrument and high-temperature curing kettle devices, the triaxial compressive strength, elastic modulus and Poisson’s ratio of the cement sheath have been obtained. On this basis, the cohesion and internal friction angle of cement sheath have been calculated according to Moore Coulomb’s law. This study can provide theoretical basis and important reference for high-temperature cementing
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