Experimental Measurements of mechanical parameters of Class G cement
- Catalin Teodoriu | Zhaoguang Yuan (Texas A&M University) | Jerome Schubert (Texas A&M University) | Mahmood Amani (Texas A&M U at Qatar)
- Document ID
- Society of Petroleum Engineers
- SPE/EAGE European Unconventional Resources Conference and Exhibition, 20-22 March, Vienna, Austria
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 1.2.3 Rock properties, 5.4.6 Thermal Methods, 5.9.2 Geothermal Resources, 3 Production and Well Operations, 1.14.3 Cement Formulation (Chemistry, Properties), 1.14 Casing and Cementing
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The new quest of unconventional resources is the achievement of well integrity which is highlighted by the inadequacy of conventional cementing procedures to provide zonal isolation. High temperatures and pressures or even post-cementing stresses imposed on the cement sheath as a result of casing pressure testing and formation integrity tests set in motion events which could compromise the long term integrity of the cement sheath due to fatigue. Knowledge of the mechanism of fatigue in cement and factors that affect it such as the magnitude of the load, strength and composition of the cement, mechanical properties of the cement and pattern of load cycles are important to achieve a realistic design of a cement system that will be subjected to fatigue loading. Such a design will go a long way to ensure the long term integrity of a well operating under downhole conditions. Finite element investigations help engineers to assess the stress magnitude and evolution for a given well configuration, but when structural calculations for casing-cement system are required, missing input parameters reduce the quality of the results.
In order to have reliable data we performed an extensive experimental work using Class G cement in order to measure the principal parameters for mechanical structural calculations: compressive and tensile strength, Young modulus, Poison Ratio. The data was measured under room conditions and elevated temperature and pressure. The results were also extrapolated for a time period for more than 300 days.
The paper will provide an excellent data inventory for class G cement that can be used when mechanical studies on cement, like finite element studies, are required.
Providing zonal isolation for the life of a well to allow the safe and economic production of oil and gas is the main purpose of the annular cement. For an oil/gas well to maintain its integrity and be produced effectively and economically, it is pertinent that a complete zonal isolation is achieved during the life of the well. This complete zonal isolation, however, can be compromised due to factors that come into play during the operative life of the completed well. Such factors may come in the form of thermal or pressure loads generally regarded as HTHP (High Temperature-High Pressure) loads which can manifest themselves as static/cyclic loads or both depending on how it is exerted.
Oilwell cement is subjected to failure mainly by the process of:
• Radial Cracking
• Cement plastic deformation
These are not new failure modes but just a petroleum engineer's term for the usual failure modes in mechanics of materials. Debonding can also be regarded as shear failure and can exist in two forms; debonding from casing and debonding from formation. It is however important to note that debonding can also occur as a result of cement shrinkage and in this case cannot be regarded as a failure due to shear. Radial cracking is a failure mode by fracture which is as a result of the gradual growth of cracks when the cement is subjected to fatigue loading. Usually, the surface exhibits no sign of deformation and will finally fail under a gradually increasing load perpendicular to the loading axis in tension and inclined to the loading axis in compression. Plastic deformation is as a result of yielding failure. It usually results in the change of shape of the material involved.
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