Cement Mechanical Property Measurements Under Wellbore Conditions

Reddy, B.; Santra, Ashok; McMechan, D.E.; Gray, D. J.; Brenneis, Chad; Dunn, Rick

doi:10.2523/95921-ms

Cited by 6 publications

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“…Selected plain cement formulations were tested in uniaxial and triaxial compression at elevated temperature of 392 0 F. In order to get better cements mechanical propties in field conditions, the cement mechanical properties were measured under wellbore conditions (B.R. Reddy et al 2005) with the temperature of 190 0 F and the pressure of 3,000 psi. Portland and non-portland based cement formulations containing a variety of admixtures and foamed-cement samples were used.…”

Section: Introductionmentioning

confidence: 99%

Experimental Measurements of mechanical parameters of Class G cement

et al. 2012

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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.

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Section: Introductionmentioning

confidence: 99%

Experimental Measurements of mechanical parameters of Class G cement

et al. 2012

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“…Empirical equations were used by Di Lullo and Rae (2000) to estimate Poisson's ratio from flexural strength and Young's modulus from compressive strength. Cement static and dynamic mechanical properties were compared by Reddy et al (2007). It was observed that dynamic mechanical properties are considerably larger than the static ones.…”

Section: Introductionmentioning

confidence: 99%

Finite Element Simulation of Downhole Stresses in Deep Gas Wells Cements

Nabipour

Joodi²,

Sarmadivaleh

2010

All Days

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Deep gas reservoirs are going to play more important roles in meeting growing demand of natural gas throughout the world. Due to extreme conditions of downhole stresses, pressure and temperature that occur in deep gas wells, maintaining cement mechanical integrity and zonal isolation have become critical concerns of industry during drilling, completion, and production of such wells. Cement sheath is expected to provide a flawless annular seal between casing and formation along the wellbore. However; cement failure cases which are being reported regularly show that there is still need for understanding extreme downhole conditions and the behavior of cement sheath experiencing such an environment. Although Uniaxial Compressive Strength (UCS) of cement is commonly regarded as the most important mechanical property of cement, recent theoretical and experimental results show that other mechanical properties of cement can be even more determinative in its failure.In this study, Finite Element Method (FEM), a widely-used robust numerical tool, is used for simulation of the downhole environment by modeling temperature, pressures, stresses, downhole materials and their interactions. Using this approach magnitude, direction and type of induced stresses in casing, cement, and formation have been determined. Furthermore; a series of sensitivity analyses was performed to reveal the effects of variation of various parameters such as casing internal pressure, differential horizontal stress and casing eccentricity, on the induced stresses in the cement sheath.Radial, tangential and von Mises stress profiles in the deep gas wells cements were investigated. Furthermore, the effect of casing internal pressure, differential horizontal stress and casing eccentricity were studied in the model. Results show that deep gas wells' cements experience extreme amounts of thermal and mechanical stresses and special consideration is required in cement selection.

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Zonal Isolation Modeling and Measurements—Past Myths and Today's Realities

James

Boukhelifa²

2006

Abu Dhabi International Petroleum Exhibition and Conference

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Over the past ten years, several papers have been published discussing the long-term mechanical durability of the cement sheath. The customary procedure is to use a model to predict potential failure scenarios and to subsequently design a sealant material that will not fail under the expected conditions. The predictive models are either analytical or finite-element models. The analytical models can only be applied to relatively simple situations that require a simplified set of input data. In these cases, the results are consistent with those of finite-element models. More complex situations can be simulated with finite-element models, but the input data requirements are far more severe. Typically in the modeling papers, little information is included on how the input data is obtained. Because of this, several papers have been published that proposed ways to obtain the input data, in particular the mechanical parameters of the set cement. However, because these papers have typically addressed only one or two parameters, the proposed methods are inconsistent. This paper critically reviews the published information; highlights the strengths and weaknesses of the various approaches, and recommends a self-consistent set of measurement methods. The predictions from the given approach have been verified at the field level through evaluation of actual wells. Introduction The effect of pressure and temperature changes on the integrity of the cement sheath was demonstrated experimentally many years ago.1,2 More recently, this behavior has been modeled using both analytical3 and finite-element4 models. Athough finite-element models are capable of handling more complex situations, they are usually used with simplifying assumptions in which case they offer no advantages over analytical models. Indeed, Bosma et al.4 used the analytical model and results from reference 3 as a benchmark for their finite-element model and showed good agreement between the two models. Formation creep, which can potentially induce large strains in the cement sheath, was also discussed by Bosma et al., but this will not be addressed in this paper. Both types of models assume a linear elastic mechanical behavior. Therefore, the response of the cement sheath to strain is determined by the static Young's modulus and Poisson's ratio of the cement through Hooke's law. A correction of dynamic values of Young's modulus and Poisson's ratio is required to be used in Hooke's relationship. The failure point is given by either the tensile strength or the compressive strength of the cement (using the Mohr-Coulomb failure criterion for the latter), depending on the expected failure mechanism. In general, decreasing the Young's modulus or increasing the Poisson's ratio of the cement will decrease the stresses induced in the cement sheath and, for a given situation, will decrease the risk of failure. In the modeling papers discussed above, there has been little discussion of how to determine the appropriate parameters that describe the cement mechanical behavior. Thiercelin et al.3 determined the Young's modulus in flexion and flexural strength (Mr) from three-point bending tests. The authors noted that the loading rate is a key parameter in determining the ultimate strength of the material: the lower the loading rate the lower the flexural strength measured. They applied a safety factor of 50% to the flexural strength to obtain a tensile strength value more representative of downhole conditions. However, as three-point bend tests were performed, there was no way to determine the Poisson's ratio of the cement; so, the value was estimated at 0.2. The model described was a linear thermo-elastic model, so the use of a single value of Young's modulus and Poisson's ratio was appropriate. Bosma et al.4 used confined triaxial and unconfined uniaxial measurements to characterize the cement behavior but did not give details of the experimental methods used. Although the authors discussed nonlinear failure behavior, the prefailure behavior was described by a single value of Young's modulus and Poisson's ratio, suggesting a linear-elastic model was used. This lack of discussion on the test methods used to determine the cement behavior input data has been recognized by several authors, and there have been several papers published that discussed ways to measure mechanical parameters of set cement, but none have provided a complete package of measurements.

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Cement Mechanical Property Measurements Under Wellbore Conditions

Cited by 6 publications

References 0 publications

Experimental Measurements of mechanical parameters of Class G cement

Experimental Measurements of mechanical parameters of Class G cement

Finite Element Simulation of Downhole Stresses in Deep Gas Wells Cements

Zonal Isolation Modeling and Measurements—Past Myths and Today's Realities

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