تعیین تنش برجا جهت بررسی آنالیز پایداری چاه تحت شرایط همسان‌گردی عرضی

نوع مقاله: مقاله پژوهشی

نویسندگان

دانشکده معدن و متالورژی، دانشگاه صنعتی امیرکبیر، تهران،‌ ایران

چکیده

تنش‎های برجا فاکتوری کلیدی است که در بسیاری از مسائل مرتبط با سنگ و در زمینه‎های مهندسی نفت نظیر پایداری دیواره چاه و شکست هیدرولیکی از اهمیت بالایی برخوردار است. عمدتاً از روش‎های مستقیم که پرهزینه و زمان‎بر هستند؛ جهت تخمین تنش‎های برجا استفاده می‎شود. همچنین روش‎های مستقیم نتایج را محدود به عمق خاصی می‎کنند که نمی‎توان آن‎را به کل چاه تعمیم داد. در این مقاله از دو روش غیرمستقیم پرکاربرد در تخمین تنش برجا یعنی مدل مبتنی بر مدول برشی و روابط پوروالاستیک در محیطی تحت شرایط همسان‌گردی عرضی، استفاده و نتایج مورد بحث و بررسی قرار گرفته‎اند. محاسبه پارامترهای الاستیکی، مقاومت سنگ و تنش برجا بر اساس فرضیات هر روش برای یک چاه عمودی حفر شده در جنوب غربی ایران نشان داد روش مبتنی بر مدول برشی روش پیشنهادی برای پیش‎بینی حداکثر تنش افقی است. در این روش مقدار ضریب آکوستوالاستیک 52/0 در نظر گرفته شد. همین‎طور نسبت C66/C44 کمـتر از 3 است که چندان قابل قبول نیست. تنش‎های برجای به‌دست آمده با این روش با مغزه‎ها کالیبره شده‎اند. هرچند این روش رژیم گسلی منطقه را درست پیش‎بینی کرده ولی مقدار تنش با توجه به مدل مکانیکی ساخته شده کمتر از مقدار واقعی تخمین زده است و نتایج با نمودار کالیپر همخوانی ندارد. اما مدل مکانیکی ارائه شده به‌وسیله روابط پوروالاستیک که یک رویکرد بهتری در پیش‎بینی تنش برجا تحت شرایط همسان‎گردی عرضی داشته تطابق بهتری با نمودار کالیپر دارد و فواصلی که دچار شکستگی برشی و کششی شده بخوبی نشان داده‌اند که این می‎تواند به علت وجود لایه‎های شیلی درون سازند باشد.
 

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

In-Situ Stress Estimation Techniques for Wellbore Stability Analysis Under Transverse Isotropic Condition

نویسندگان [English]

  • Ramin Mohammadi
  • Hamidreza Ramazi
Mining and Metallurgy Faculty, Amirkabir University of Technology, Tehran, Iran
چکیده [English]

In situ stresses are considered as pivotal factors in rock sciences in addition to petroleum engineering issues including wellbore stability and hydraulic fracturing. In situ stresses are mainly estimated by costly and time consuming methodologies directly. Moreover, the outcomes of these approaches are limited to a certain depth of the well. Therefore, these methods cannot be generalized. In the present study, a model based on the shear moduli and Poro-elastic parameters in an environment under transverse isotropic conditions has been employed whereby the results further discussed. Elastic parameters, strength, and in situ stress according to the hypotheses underlying the both models were calculated for a well in the west of Iran. Shear moduli-based method is proposed to predict the maximum horizontal stress. Here, acoustoelastic parameter was set to 0.52. Of course, C66/C44< 2 is not much acceptable. However, the stresses were calibrated using the cores. Although this method enabled to predict the revers faulting regime correctly, however regarding the model, stress has been underscored and the outputs are not consistent with the calliper log. Subsequently, Poro-elastic based mechanical model in accordance with caliper log estimated a more reliable in situ stress under transverse isotropic conditions. Furthermore, break-out and break-down have been properly determined that could be due to the shale layers within the formation.
 

کلیدواژه‌ها [English]

  • In Situ Stress
  • Transversely Isotropic
  • Wellbore Stability
  • Mechanical Earth Model
  • Poro-Elastic Equations and Mohr-Coulomb Criterion

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