اثرات ژئومکانیکی افت فشار مخزن، دمای سیال حفاری و فشار اسمزی بر روی شرایط پایداری دیواره چاه (مطالعه موردی)

نوع مقاله: مقاله پژوهشی

نویسندگان

دانشکده مهندسی نفت و گاز، دانشگاه صنعتی سهند، تبریز، ایران

10.22078/pr.2019.3809.2752

چکیده

ناپایداری دیواره چاه همواره یکی از مهمترین مشکلات در حین حفاری بوده است. به طور معمول، تعیین وزن سیال حفاری جهت پایداری دیواره چاه در حین حفاری، در شرایط اولیه مخزن انجام می‌شود. در حالیکه بعد از تولید از مخزن، با گذشت زمان، فشار منفذی لایه تولیدی در صورت نبود منبع فشار کاهش می‌یابد و باعث تغییر در مقدار و جهت تنش‌های برجا می‌شود. در این شرایط به منظور حفظ پایداری دیواره در حفاری چاه‌های جدید لازم است که اثر افت فشار مخزن جهت تعیین شرایط پایداری و مسیر بهینه در نظر گرفته شود. همچنین دیگر عوامل اثر گذار در پایداری دیواره چاه دمای سیال حفاری و اثر اسمزی آن می‌باشد. در این تحقیق به منظور بررسی اثر افت فشار مخزن بر روی شرایط پایداری چاه و مسیر بهینه حفاری و همچنین بررسی اثر اسمزی و دمای سیال حفاری، یکی از مخازن جنوب غرب ایران که دچارMPa 11 افت فشار شده است، مورد مطالعه قرار گرفت. در شرایط اولیه این مخزن حداقل فشار درون چاهی مورد نیاز جهت عدم ریزش دیواره چاه در محدوده 4/28 - MPa 2/34 بوده است و پایدارترین مسیر حفاری، حفر چاهی با زاویه ˚45 و در جهت تنش افقی حداقل می‌باشد. پس از کاهش MPa 11 فشار مخزن، با تغییر تنش‌های القایی اطراف دیواره چاه، حداقل فشار لازم جهت پایداری در محدوده 7/21-MPa 4/26 و پایدارترین مسیر حفاری ˚10 کاهش، چاهی با زاویه ˚35 می‌باشد. همچنین با در نظر گرفتن اثر دمای سیال حفاری بر روی این مقادیر، حداقل فشار لازم در چاه با مقداری کاهش در محدوده 4/21-MPa 26 می‌باشد و همچنین با اعمال اثر شیمیایی سیال حفاری بر روی محتوای رسی سازند این مقدار با مقداری افزایش در محدوده 22-MPa 7/26 می‌باشد. نهایتاً با در نظر گرفتن همزمان اثر اسمزی و دمای سیال به دلیل اثر معکوسی که دارند حداقل فشار لازم جهت پایداری در محدوده 8/21-MPa 5/26 می‌باشد. بنابراین، اثر افت فشار مخزن تأثیر قابل توجهی بر روی پایداری دیواره چاه دارد و سایر موارد در مخزن مورد مطالعه تأثیر کمی دارند.
 

کلیدواژه‌ها


عنوان مقاله [English]

Geomechanical Effects of Reservoir Pressure Drop and Drilling Fluid Temperature on Wellbore Stability Conditions

نویسندگان [English]

  • Ehsan Cheraghsahar
  • Reza Falahat
  • Seyyed Alireza Tabatabaei-Njad
Faculty of Petroleum Engineering, Sahand University of Technology, Tabriz, Iran
چکیده [English]

The instability of the wellbore has always been one of the major problems during drilling. In order to maintain the wellbore stability during drilling, the weight of drilling fluid is normally estimated to be decreased in the initial condition of reservoir. However, after reservoir production, the pore pressure of these layers decreases in case of having no pressure support. This change affects the magnitude and direction of in-situ stresses. In this situation, in order to maintain the wellbore stability for drilling new wells, it is necessary to consider the effect of reservoir pressure drop to determine the stability conditions and optimum well trajectory. Other factors affecting the stability of the wellbore are osmotic effect and drilling fluid temperature. In this research, one of the reservoirs in the Southwest of Iran was investigated. This reservoir underwent a pressure drop of 11 MPa during the production. The impact of reservoir pressure drop, osmotic effect and drilling fluid temperature are investigated on the wellbore stability condition and the optimum drilling trajectory. In the initial conditions of this reservoir, the minimum collapse pressure is in the range of 28.4–34.2 MPa, and the most stable drilling trajectory is a well with inclination of 45˚ in direction of minimum horizontal stress. After a pressure drop of 11 MPa that causes changes in induced stresses around the wellbore, the minimum collapse pressure for the stability decreases to the range of 21.7–26.4 MPa, and the most stable drilling trajectory, with 10˚ reduction in inclination, is a well with inclination of 35˚. In addition, including the effect of drilling fluid temperature, the minimum collapse pressure in the well is negligibly impacted to be in the range of 21.4 -26 MPa. Also, chemical effect of drilling fluid on the formation clay content increased minimum collapse pressure to the range of 22-26.7 MPa. Finally, considering both osmotic effect and fluid temperature estimates minimum collapse pressure in the range of 21.8-26.5 MPa. Therefore, the reservoir pressure drop has a significant effect on the wellbore stability condition, and other factors have negligible impacts on this reservoir.
 

کلیدواژه‌ها [English]

  • Geomechanics
  • Wellbore Stability
  • Pressure Drop Effect
  • Drilling Fluid Temperature
  • Osmotic Effect
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