M. Hemmatian; B. Tokhmchi; V. Rasouli; R. Gholami
Abstract
A good knowledge of the parameters causing casing damage is critically important due to vital role of casing during the life of a well. Cement sheath, which fills in the gap between the casing and wellbore wall, has a profound effect on the resistance of the casing against applied loads. Most of the ...
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A good knowledge of the parameters causing casing damage is critically important due to vital role of casing during the life of a well. Cement sheath, which fills in the gap between the casing and wellbore wall, has a profound effect on the resistance of the casing against applied loads. Most of the empirical equations proposed to estimate the collapse resistance of casing ignore the effects of the cement sheath on collapse resistance and rather assume uniform loading on the casing. This paper aims to use numerical modeling to show how a bad cementing job may lead to casing damage. Two separate cases were simulated where the differences between good and bad cementation on casing resistance were studied. In both cases, the same values of stresses were applied at the outer boundary of the models. The results revealed that a good cementing job can provide a perfect sheath against the tangential stress induced by far-field stresses and reduce the chance of casing to be damaged.
A Chamani; Vamegh Rasouli
Abstract
The rapid growth in natural gas consumption has increased the need for gas storage, in particular in the form of injection into depleted reservoirs. Also, CO2 sequestration into the depleted reservoirs has attracted a large attention recently. However, it is important to ensure that the injection pressure ...
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The rapid growth in natural gas consumption has increased the need for gas storage, in particular in the form of injection into depleted reservoirs. Also, CO2 sequestration into the depleted reservoirs has attracted a large attention recently. However, it is important to ensure that the injection pressure is maintained below a certain limit to avoid unsealing the cap rock or reactivation of any existing fracture planes within or above the reservoir rocks. In particular, it can be thought that gas injection into formations with non-horizontal structures, such as anticlines, is more problematic than horizontal formations due to the development of shear zones in such geometries. This could potentially result in long term wellbore problems such as casing collapse or shearing along a fault or fracture plane intersecting the wellbore. In this study we compare the stress profile changes before and after gas injection into three structures: a horizontal and two anticline formations with different slopes at their flanks. For this purposes a 3D numerical simulator was used. The program was developed using finite element method (FEM) and the code was written in Fortran.The stress magnitudes along curved profiles were compared for three structures at a similar depth. A limited extension of a porous zone was assumed in this study. The results indicate how as structure becomes more curvy in its geometry the likelihood of shear displacement increases.
