HPHT Cement Sheath Integrity Evaluation Method for Unconventional Wells

Abstract

Chances of cement sheath failure increase considerably when the application involves deepwater, high pressure high temperature (HPHT) conditions. Such failures 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 (SAGD), production, completion, or other remedial treatments. Thermal and stress cycles could impose the risk of losing zonal isolation and lead to delay in hydrocarbon production.Cement mechanical properties measurment solely would not be sufficient to predict the failure threshold of a cement sheath. Some experimental studies were conducted about the effect of cyclical loading on the integrity of casing and drill strings but less research have been done about the in situ cement sheath integrity under cyclical loading. This paper introduces a new Ultra HPHT experimental set up and an applicable method to evaluate cement sheath integrity under cyclical loading. It also provides insights to find the cement fatigue failure cycle for the set cement at elevated pressures and temperatures.This system was built and completed by benefiting from the capabilities of an extreme HPHT Rheometer. Cement samples could be cured for number of hours in the newly developed HPHT cell and then instantly tested under cyclical loading in various scenarios at high temperatures. The cement sheath fails after a certain number of cycles when reaches its fatigue endurance limit. This research showcases scenarios in which the fatigue failure cycles were identified for 1,000 psi, 2,000 psi and 5,000 psi, pressure differentials between the confining pressure (exposed to outside of the sheath) and the casing pressure. During these experiments, the confining pressure and temperature were held constant at 15,000 psi and 330 ̊ F while the casing pressure varied cyclically between 15,000 psi and 16,000 psi (Set A), 17,000 (Set B) and 20,000 (Set C). A stable chemistry of Class H cement plus 35% silica was used to prevent cement retrogression. Cement sheath failures such as radial cracking, debonding and disking occured due to cyclical loadings. Finally, a fatigue failure envelope was generated by the obtained data. This curve represents the extent of cement sheath endurance at HPHT conditions under cyclical loading.

Development and Application of Novel Sodium Silicate Microcapsule-Based Self-Healing Oil Well Cement

“…The imposed stresses therefore have the potential to induce cracks in the cement column and create microannuli [2]. Weak bonding can cause failure at cement-casing or cement-formation interfaces [3,4]. These defects in the cement sheath could adversely affect their sealing capacity to provide zonal isolation, resulting in gas/liquid migration through the flow paths created by cement failure and even serious leak or blowout accidents.…”

Cement sheath modification using nanomaterials for long-term zonal isolation of oil wells: Review

“…Properties impacting zonal isolation in this period include fluid loss (filtration), free fluid development (bleeding), gel strength development, chemical shrinkage, and permeability (Nelson and Guillot, 2006). The required short-term properties are summarized below (Nelson and Guillot, 2006;Ravi et al, 2002;Shadravan et al, 2014;Williams et al, 2011) :…”

“…As described in the previous section, cement sheaths typically fail because of volumetric instability and imposed tensile stresses beyond the tensile strength of the cement sheath. (Shadravan et al, 2014;Williams et al, 2011) Pressure increase is more damaging because the fluid injection lasts from minutes to hours (Thiercelin et al, 1998) Several have suggested requirements to tensile strength, Young's modulus, and other mechanical properties of the cement sheath to provide a long-term zonal isolation through long-term stress evaluation (Bois et al, 2011;Bois et al, 2012;Roy-Delage et al, 2000;Saint-Marc et al, 2008;Stiles and Hollies, 2002). Thiercelin et al (1998) analyzed different stress conditions in oil wells which were applicable for most types of loading.…”

“…From cement sheath perspective, as hydrocarbon resources are becoming gradually depleted in easy-to-recover environments, hostile downhole conditions are more common (Jimenez et al, 2016). Additionally, thermal and stress cycles created by well events such as hydraulic fracturing, production, completion, steam injection, or remedial treatments during the well's life, poses significant challenges to the cement sheath integrity (Shadravan et al, 2014). Therefore, taking new approaches are required to design a cement system to withstand the potential severe conditions during well's life cycle.…”

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).…”