شبیه‌سازی عددی اثر تنش‌های برجا برروی انرژی ویژه تیغه‌ PDC با استفاده از روش المان‌مجزا

نوع مقاله: مقاله پژوهشی

نویسندگان

گروه استخراج معدن، دانشکده مهندسی معدن و متالورژی، دانشگاه یزد، ایران

10.22078/pr.2019.3253.2502

چکیده

در حفاری چاه‌های نفت و گاز، یکی از عوامل موثر و تاثیرگذار در نرخ نفوذ حفاری و مقدار انرژی ویژه (انرژی مورد نیاز برای حذف حجم واحدی از سنگ)، فشار محصورکننده یا به عبارتی دیگر فشار ته چال است. عملیات برش سنگ ترکیبی از دو حالت شکست شکننده و تغییر شکل‌پذیر است. هر کدام از این حالات شکست، تاثیر متفاوتی برروی انرژی ویژه و ساختار مواد خرد شده و در نتیجه نرخ نفوذ حفاری دارد. در این مقاله جهت درک ارتباط بین حالت شکست سنگ و فشار محصورکننده و تاثیر آن برروی انرژی ویژه از روش عددی المان مجزا استفاده شده است. برای این منظور در این تحقیق از نرم‌افزار عددی کد جریان اجزاء که رفتار مکانیکی مواد دانه‌ای را با روش المان‌های مجزا شبیه‌سازی می‌کند، استفاده شده است. براساس نتایج به‌دست آمده در شرایط بدون فشار، نیروی اعمالی از تیغه باعث شکست اتصالات بین دانه‌ای در یک صفحه‌ای شکست می‌شود. اما در شرایط فشار محصورکننده، مکانیزم متفاوتی در حال وقوع است و اختلاف فشار به‌وجود آمده باعث نگه داشتن مواد خرد شده برروی همدیگر و افزایش انرژی ویژه می‌شود. همچنین تا فشار حدود MPa 26 با افزایش میزان تنش، انرژی ویژه افزایش نسبتاً خطی دارد. اما بعد از این فشار به‌دلیل افزایش تنش‌های محصورکننده و شرایط نزدیک به لیتواستاتیک، روند افزایشی انرژی ویژه نسبت به افزایش عمق کاهش می‌یابد.
 

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

A Discrete Element Simulation for the Effects of In-situ Stresses on the Mechanical Specific Energy of PDC Drill Bits

نویسندگان [English]

  • Amirhosein Mazruee
  • Mohammad Fatehi Marji
  • Mehdi Najafi
  • Mohesen Mohebi
Department of Mining and Metallurgical Engineering, Yazd University, Iran
چکیده [English]

In the drilling of oil and gas wells, confining pressure or the pressure at the well bottom is one of the effective factors affecting the rate of drilling and the amount of specific energy (the energy needed to remove a single volume of rock). In this operation, the rock cutting process is a combination of two modes of failures, i.e. brittle and ductile. Each of these failure modes has a different effect on the specific energy and structure of the crushed material, and thus on the rate of drilling. In this paper, the distinct element method is used to understand the relationship between rock fracture and confining pressure and its effect on the specific energy. For this purpose, a particle flow code is used that numerically simulates the mechanical behavior of the granular materials such as rocks. Based on the results obtained in condition of no confining pressure, the force applied to the cutter blade causes failure of the inter-granular connections in a single failure plane. But under confined pressure conditions, a different mechanism is taking place, and the difference in pressure created during the cutting action of PDC drill bits keep the crushed rock on each other and increase the mechanical specific energy of the rock cutters. Also, up to a pressure of about 26 MPa, with increasing tension, the specific energy has a relatively linear increase during the cutting action of the bits. But after this pressure due to the increased confining stresses and near-hydro-static conditions, the incremental increase in the mechanical specific energy decreases as the drilling depth increases.
 

کلیدواژه‌ها [English]

  • Discrete Element Method
  • Rock Failure
  • Specific Energy
  • In Situ Stress
  • PFC2D

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