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Modeling of Mechanical Damage in Fractured Rocks During Drilling

Gomar, Mostafa | 2015

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 47694 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Goodarznia, Iraj; Shadizadeh, Reza; Massihi, Mohsen
  7. Abstract:
  8. Effective stress variation is one of the main issues in petroleum and gheothermal reservoir development. These stress variation could cause formation damage, sand production, sloughing shale and various modes of borehole instability like induced fractures and borehole wall shearing. In petroleum engineering, drilling a borehole is the first step in reservoir development. The wellbores are implemented to produce or inject fluids such as water, oil, gas and chemical fluids used during secondary and tertiary recovery processes. Upon drilling a borehole, reservoir pore pressure, rock and fluid temperature and mechanical stresses change which induces borehole instability and variations in rock matrix and fracture permeability. In this dissertation, three important issues regarding drilling process are investigated. These are borehole istability, matrix and fracture permeability change. In these phenomena, fluid pressure and temperature and mechanical stress distribution are calculated utilizing thermoporoelastic concept and finite element technique for various initial and boundary conditions. Four rock failure criteria are applied to study borehole stability. Experimental based correlations and theoretical equations are implemented to investigate matrix permeability variation. Finally, fracture permeability variation is modeled utilizing a hybrid numerical method combining finite element and boundary element techniques. The result show that maximum variation in effective stresses occur around borehole and their values may exceed ±40 . The main reasons for borehole breakout stabilization are decreare in tangential stress and increase in confining radial stress. Maximum variation in matrix permeability occurs around borehole. In longer distances away from borehole wall, the changes in mechanical stresses become negligible while fluid pressure and temperature variation become important. Maximum variations in fracture permeability occur around borehole. In fracture networks where fractures are inclined with respect to in situ stresses, shear stresses are one of the main influencing factors in fracture permeability variation. In verbalanced condition, because of convection heat transfer, fracture permeability variations envelop larger area. In general, continuous variation in fluid pressure, temperature and in situ mechanical stresses induces borehole instability and variation in matrix and fracture permeability which require constant monitoring during drilling and production in petroleum and geothermal reservoirs
  9. Keywords:
  10. Fracture Permeability ; Boundary Element Method ; Finite Element Method ; Fractured Reservoirs ; Displacement Discontinuity Method ; Matrix Permeabilility ; Borehole Stability ; Drilling Operation

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