محاسبه پیشروی کرمچاله‌ها و ضریب پوسته حین اسیدکاری چاه‌های جهت‌دار در مخازن کربناته

نوع مقاله : مقاله پژوهشی

نویسندگان

دانشکده مهندسی شیمی و نفت، دانشگاه صنعتی شریف، تهران، ایران

چکیده

اسیدکاری گسترده روشی برای بهبود عملکرد جریان ورودی به چاه است. در این عملیات، محلول اسیدی به‌منظور افزایش تراوایی مخازن کربناته‌ در ناحیه نزدیک چاه، از طریق تشکیل سریع کانال‌هایی با شکل بی‌قاعده‌ تحت عنوان کرمچاله به درون سازند تزریق می‌شود. روش‌های معمول دیگر جهت بهبود تولید در مخازن کربناته شامل شکاف هیدرولیکی، شکاف اسیدی، مشبک‌کاری با جت سیال و ترکیب اسیدکاری و مشبک‌کاری چاه‌های دارای تکمیل لوله جداری می‌باشد. هدف از این پژوهش، محاسبه میزان پیشروی کرمچاله‌ها در یک لایه کربناته افقی (شیب لایه=0) به هنگام تزریق اسید از یک چاه جهت‌دار که به‌صورت حفره‌باز یا حفره‌بسته تکمیل شده است، می‌باشد تا بدین‌طریق، تغییرات ضریب پوسته در برابر زمان محاسبه شود. بدین منظور از مدل نیمه‌تجربی بویجس و گلسبرگن برای شبیه‌سازی پیشروی کرمچاله‌ها در ابعاد میدانی براساس برازش با داده‌های آزمایشگاهی نمودار بازدهی اسید، یک مدل توزیع فشار ناپایای ایجادشده درون سازند ناشی از یک چاه جهت‌دار و همچنین، یک مدل تک‌فازی جریان سیال نیوتنی درون چاه با درنظر گرفتن اثر ورود و خروج سیال از طریق دیواره چاه، استفاده شده است تا از حل همزمان معادلات این سه مدل در کنار هم بتوانیم میزان پیشروی کرمچاله‌ها در هر بازه زمانی را به دست آوریم. براساس نتایج به‌دست‌آمده، میزان پیشروی کرمچاله‌ها در لایه مخزنی با افزایش عمق کاهش می‌یابد چراکه با شروع اسیدکاری، تراوایی قسمت‌های بالایی لایه مورد نظر افزایش بیشتری به دلیل تماس سریعتر اسید با آن‌ها، می‌یابد که منجر به دریافت اسید بیشتر و درنتیجه عمق نفوذ بالاتر کرمچاله‌ها در قسمت‌های بالایی لایه می‌شود. همچنین، تکمیل حفره بسته نسبت به تکمیل حفره‌باز، باعث افزایش پیشروی کرمچاله‌ها و در نتیجه بهبود عملیات اسیدکاری مخازن کربناته می‌شود. لازم است تعداد بهینه زیرلایه‌های مورداستفاده در شبیه‌سازی به منظور دقت و سرعت مناسب محاسبات در نظر گرفته شود تا بتوان از صحت نتایج اطمینان حاصل کرد. افزایش زاویه چاه تنها تا یک عمق خاص باعث افزایش پیشروی کرمچاله‌ها می‌شود، اما این به‌معنای بهبود عملیات اسیدکاری و کاهش ضریب پوسته نیست، بلکه حداقل ضریب پوسته در یک زاویه خاص ایجاد می‌شود که باید در طراحی چاه‌های جهت‌داری که مخزن آن‌ها حتماً به اسیدکاری نیاز دارد، درنظر گرفته ‌شود.
 

کلیدواژه‌ها


عنوان مقاله [English]

Calculating Wormhole Propagation and Skin Factor in Carbonate Reservoirs during Directional Wells Acidizing

نویسندگان [English]

  • Mohammad Mehdi Kardooni
  • Saeid Jamshidi
Chemical and Petroleum Engineering Department, Sharif University of Technology, Tehran, Iran
چکیده [English]

Matrix acidizing is a method for improving well inflow performance. In this operation, acidic solution is injected into the carbonate formation to increase near wellbore permeability by rapid creation of irregularly shaped channels named “wormholes”. Other common carbonate stimulation techniques include: hydraulic fracturing, acid fracturing, hydro-blasting and combination of acidizing and cased-hole perforation. In this research, we aim to calculate wormhole propagation in a horizontal carbonate later (bed dip=0) during acidizing a directionally drilled well which is open-hole or cased-hole and thus modeling skin factor evolution with time. For this purpose, Buijse-Glasbergen semi-empirical field scale wormhole propagation model based on regression with acid efficiency curve, a model for unsteady-state pressure distribution in the formation caused by a directionally drilled well and a model for single phase Newtonian fluid flow in the wellbore considering inflow/outflow from wellbore wall are coupled which by solving them simultaneously, wormhole propagation in each time step can be calculated. Based on the obtained results, wormhole propagation decreases with reservoir layer depth due to the fact that by starting acidizing job, permeability of the upper portions of the layer will increase more than the lower parts as a result of the sooner contact of the acid with them. Thus, these parts will receive larger volumes of acid and greater wormhole penetration depths. Also, wormhole propagation radius will be increased in a cased-hole completion in comparison with the open-hole and thus  carbonate reservoirs acidizing results will be improved. It is required to consider optimum number of sublayers used in simulation based on reasonable precision and runtime to obtain accurate results. Increasing wellbore inclination causes wormhole propagation to be increased to a specific depth, but it does not necessarily improve overall acidizing results and reducing skin factor. Minimum skin factor occurs in a specific inclination which must be considered in planning directional wells which their reservoirs will require acidizing certainly.
 

کلیدواژه‌ها [English]

  • Carbonate Reservoir Acidizing
  • Directional Well
  • Wormhole Propagation
  • Unsteady-state Reservoir Pressure Distribution
  • Cased-hole Completion
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