Effects of Long-Term Exposure to Ultrahigh Temperature on the Mechanical Parameters of Cement

Abstract

TX 75083-3836, U.S.A., fax 1.972.952.9435. AbstractLong-term mechanical durability of a cement sheath exposed to stresses in a wellbore environment is critical to maintaining zonal isolation for the life of a well. The ability of a cement sheath to remain intact when exposed to changing wellbore stresses is highly dependent upon the parameters of Young's Modulus, Poisson's Ratio and tensile strength of the cement and the surrounding rock. Wellbore stresses sufficient to cause failure of a cement sheath may result from changes in temperature, casing pressure, formation pressure, or nearwellbore tectonic stresses.Wells subjected to Cyclic Steam Stimulation (CSS) for heavy oil recovery undergo extreme temperature changes that impart substantial stresses on the cement sheath. During CSS, wellbore temperatures can fluctuate between 77°F and 645°F, potentially leading to cement sheath failure. Various Finite Element Analysis models exist that are useful in predicting the failure potential of a cement sheath. These models require input of cement mechanical parameters. Mechanical parameters of numerous cement formulations have been measured in recent years but none of those measurements was made after long-term exposure of the cement to the ultra-high temperatures encountered in CSS wells. Development of such data was required to model the risk of cement sheath failure in wells subjected to CSS.This paper presents a test methodology for measuring the mechanical parameters of five cement formulations after exposure to a temperature of 645°F. Parameters of Young's Modulus, Poisson's Ratio and tensile strength were measured. Evolution of these parameters over a two-year period is presented. The temperature conditions to which the cement was exposed was found to have a significant impact on the mechanical parameters. The Young's Modulus, Poisson's Ratio and tensile strength of systems exposed to 645°F varied significantly from systems exposed to an ambient temperature of 77°F. The mechanical parameters of each individual cement formulation were also markedly different. Specialized cement systems, such as foamed cement or blends containing flexible particles, did not necessarily have mechanical parameters that were better suited for use in CSS wells than some of the more conventional formulations.

Investigating temperature effect on degradation of well cement in HPHT carbonic acid environment

“…Previous similar studies (Stiles, 2006;Sauki and Irawan, 2010;Lesti et al, 2013) on compressive strength showed significant scattering in measurements. In order to minimize scattering and establish a reasonable trend, the values of compressive strength reported for each class of cement were averaged (three for unaged samples and six for aged samples).…”

“…Deschner et al (2013) showed that elevated temperature has positive influence on early compressive strength development of ordinary Portland cement during hydration. Compressive strength and Young's modulus measurement conducted after subjecting Class G cement to 340 o C (645 o F) over 0 to 2 years of curing shows improved performance within the first year due to evolution of CSH crystalline phases (Stiles, 2006). In carbonic acid environment at elevated temperature, the major mechanisms of cement degradation are CSH structural transformation, carbonation of CH and CSH, and leaching of calcium carbonate.…”

“…A C C E P T E D ACCEPTED MANUSCRIPT 3 2006b; Stiles, 2006;Kutchko et al, 2007;Lin and Meyer, 2009;Sauki and Irawan, 2010;Prisca and Mahmood, 2012;Deschner et al, 2013). At early stages of hydration, temperature influences early strength development by accelerating the growth of principal products of hydration (i.e., portlandite and CSH) and increasing rate of chemical shrinkage of cement (Bensted and Barnes, 2002).…”

Novel Steam-Resilient Cement System for Long-Term Steam Injection Well Integrity: Case Study of a Steamflooded Field in Indonesia

“…The graph on the right shows that the novel cement system can maintain its integrity even with the mechanical properties measured after 6 months of exposure to the high temperatures. Mechanical properties are based on experimental data; reference for conventional and thixotropic cement is the Stiles (2006) paper, the LCTE measurements are from the work of Chougnet-Sirapian et al (2011), and the novel cement mechanical properties are extracted from Pershikova et al (2010).…”

Evaluation of Specialized Cement System for Long-Term Steam Injection Well Integrity

“…5: a conventional system comprising cement and silica described by Stiles, 2006, and a foam cement system described by Witt, 2009. It may be concluded that to pass through the first steaming cycle, a cement system should have an optimum combination of compressive strength-to-Young's modulus ratio (CS/YM) and tensile strength-to-Young's modulus ratio (TS/YM). 5: a conventional system comprising cement and silica described by Stiles, 2006, and a foam cement system described by Witt, 2009. It may be concluded that to pass through the first steaming cycle, a cement system should have an optimum combination of compressive strength-to-Young's modulus ratio (CS/YM) and tensile strength-to-Young's modulus ratio (TS/YM).…”