Using Fatigue-Failure Envelope for Cement-Sheath-Integrity Evaluation

Abstract

Summary Tensile and shear failures are two common cement-sheath failure criteria. Tensile failure occurs when a stress on the cement surpasses the tensile strength of the cement, and shear failure happens when a stress exceeds the shear strength of the cement. The objective of this study is to introduce a laboratory method that investigates the effects of fatigue (cyclical loading) on the cement sheath. Chances of cement-sheath failure also increase when the application involves high-pressure/high-temperature conditions; therefore, this test setup is rated to 25,000 psi and 450°F. In this method, fatigue-failure cycle and stress magnitude could reveal the extent of the fatigue tolerance of different slurry designs relative to each other. One could program and adjust casing pressure (Pi), pore pressure (PP), temperature, cycle intervals, and ramp rates to conduct a cyclical-loading test automatically. Failures caused by thermal and stress loading may occur as a result of temperature and pressure-induced stresses created by well events such as hydraulic fracturing, cyclic steam injection, steam-assisted gravity drainage, production, completion, or remedial treatments. Thermal and stress cycles could impose a risk to zonal isolation and lead to a delay in hydrocarbon production. Studying such effects could be helpful in developing a better understanding of the cement-sheath-failure threshold and, in fact, could be complementary to mechanical-properties measurement. The cement sheath fails after a certain number of cycles when reaching its fatigue-endurance limit. This research showcases examples in which the fatigue-failure cycles were identified for 1,000-, 2,000-, and 5,000-psi pressure differentials between the pore pressure (exposed to the outside of the sheath) and the casing pressure. For these experiments, the pore pressure and temperature were held constant at 15,000 psi and 330°F whereas the casing pressure varied cyclically between 15,000 and 16,000 psi (Set A), 17,000 psi (Set B), and 20,000 psi (Set C).

Innovation of Annular Sealants During the Past Decades and Their Direct Relationship with On/Offshore Wellbore Economics

“…To address potential issues and help operators make well-informed decisions regarding the long-term integrity of oil and gas wells, many companies, both in the service and operation sectors, have applied to some extent a more comprehensive approach when designing OWCs, taking advantage of the evolution of OWCs, both from the chemical (new systems) and engineering (new characterization tools) perspectives, to create an optimal sealant to help ensure integrity for the life of the well (Fig. In support of this statement, many studies report successful use of such techniques in yielding optimum long-term wellbore integrity in actual or simulated downhole environments (Krusche et al 2006;Shadravan et al 2014Shadravan et al , 2015aShadravan et al , 2015bGarnier et al 2007;De Andrade et al 2015;Godoy et al 2015;McDaniel et al 2014b;Griffith et al 2004;Jain et al 2014;Wang and Dahi Taleghani 2014b;Ramos et al 2009). Multiple datasets indicate significant variations in wellbore integrity (2.6 to 75%) over different time periods (Davies et al 2014).…”

Integrity of Downscaled Well Models Subject to Cooling

“…This hypothesis has been experimentally investigated in some recent studies (Boukhelifa et al 2005;Kosinowski and Teodoriu 2012;Shadravan et al 2015). In these studies, purely mechanical loads were applied in order to mimic stresses produced by thermally induced volumetric expansion or contraction of the casing steel.…”

“…In this study, the cracks were observed only by eye through the transparent plexiglas. Shadravan et al (2015) performed differential pressure-cycling tests in a built-for-purpose highpressure, high-temperature cell. The cell design allowed controlling the temperature, pore pressure, casing pressure and cycling intervals.…”

“…The studies on thermal cycling (Boukhelifa et al 2005;Kosinowski and Teodoriu 2012;Shadravan et al 2015) have not concluded on safe temperature ranges for well operations. Several recent studies report on application of thermal loads to downscaled wellbore section models (Albawi et al 2014;De Andrade et al 2014).…”

“…;Kosinowski and Teodoriu 2012;Shadravan et al 2015) and thermal cycling of casing/cement/rock assemblies(Albawi et al 2014;De Andrade et al 2014), suggest failure of the cement sheath including debonding and/or radial cracks. Although thermal expansion/contraction of the casing during our thermalcycling experiments must have imparted some stresses on the cement sheath, no destructive changes in the cement structure were observed.…”