Structural analysis of geothermal well cements

Current design procedures are deficient when it comes to the cement/sealant used in geothermal well cementing jobs. The structural performance of the cement is based on the requirement that the cement must have a certain compressive strength. By calculating the response of the cement due to pressure/temperature (P/T) loads, the relevant stress fields are found to be sensitive to a variety of parameters in such a way that they cannot be enveloped solely by the compressive strength of the material. A similar concern also exists in the oil and gas industry. This paper presents a variety of modeling approaches that can be used to perform the necessary structural analysis from which the stress field in the cement can be evaluated. It is recommended that the design of the cement be based on the results from such structural analysis rather than on the basis of the limited requirement for compressive strength. The paper also presents parametric variations of the radial and tangential stresses in the cement that were obtained through coupled analyses of casing-cement-formation models. It is shown that the state of stress in the cement is very sensitive to (a) far-field stress and (b) the relative stiffness between the cement and the formation. (C) 2002 CNR. Published by Elsevier Science Ltd. All rights reserved.