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Integrated Geomechanical Modeling of Casing Failure; From Lab to Simulation

Taheri, Reza | 2020

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52932 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Pak, Ali; Shad, Saeed
  7. Abstract:
  8. Casing failure is one of the mainly problems of hydrocarbon fields that may cause wells out of service and impose heavy costs on oil companies. There exist many theories that may cause casing failure including: the plastic behavior of surrounding formations, the effects of reservoir depletion, over-pressured formations, weak cementing operations, fault activation, and local stresses applied on casing. In salt-rich formations, creep behavior can be the main cause of casing failure, too.The purpose of this study is to evaluate the causes affecting casing failure via experimental studies and numerical simulation with the focus on the conditions governing south-west Iranian oil fields, where the number of casing failures has increased in recent years.The first step to assess this issue carefully is to conduct the laboratory tests to determine the geomechanical characteristics at in-situ temperature and pressure conditions. Meanwhile, wellbore stability problems are commonly related to geomechanical response, so safe design of the wells passing through high pressure-high temperature deposits needs exact geomechanical analysis. Therefore, the second step includes conducting coupled geomechanical simulation to determine stresses and strains in the casing and surrounding environments. Such analysis can simulate stress-strain variations based on the various scenarios. In this research, after conducting laboratory tests to determine the geomechanical characteristics of anhydtite caprock at high pressure-high temperature conditions and the pattern of creep behavior of Gachsaran rock salt, various scenarios of casing failure were assessed comprehensively including: the effects of depletion and variations of effective stresses, the trend of safety factor due to rock salt creep, and the role of cementing operations to causes casing failure. According to the studies, it was concluded that the scenario of reservoir depletion cannot cause casing failure. This failure has occurred because of the combined effects of weak cementing and creep in the surrounding salt layer, as the failure time and depth predicted by the numerical simulation based on the proposed scenario were found to be in accordance with the real field data
  9. Keywords:
  10. High Pressure High Temperature (HPHT) ; Salt Rock ; Gachsaran Oil Field ; Casing Failure ; Caprock ; Cementing

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