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Modeling of Wellbore Stability in Shales including Proelsatic, Chemical and Thermal Effects

Rafiee Pur, Saeed | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 41441 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Ghotbi, Sirous; Pishvaie, Mahmoud Reza
  7. Abstract:
  8. Wellbore instability is one of the serious problems during drilling. This can cause delay in drilling, increasing drilling costs and in some cases well abandonment. The present project investigates the effects of non- isothermal drilling and the difference in salt concentration between formation fluid and drilling fluid on the stability of wellbores drilled in the saturated porous shale formations subjected to an arbitrary stress field. This project also focuses on the analysis of wellbore stability in shale formations in which the thermal diffusivity is higher than fluid invasion and the mechanism of heat transfer is dominated by conduction. The governing equations used in this dissertation are based on the porothermoelasticity theory modified for shale formations. The equations have been solved numerically using fully implicit finite difference approach. Based on the model presented here, a computer program has been developed for calculation of pore pressure, temprature, salt concentration profiles and stress distribution near the wellbore. The solution algorithm consists of determination of solute concentration and temperature profiles from the relevant equations and then using hydraulic diffusivity equation, the modified pore pressure is obtained and finally the induced- stresses are calculated; After that, the modified stress values are inserted into a convenient failure index and then stability or instability of the wellbore is checked. The model presented here is a novel method in the scope of porothermoelasticity modeling and is a useful tool in evaluation of mechanical, chemical and thermal effects on the wellbore stability in shales
  9. Keywords:
  10. Numerical Method ; Wellbore Instability ; Mechanical, Chemical and Thermal Effects ; Porothermoelasticity Theory ; Shale Formation

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