Experimental Study of the Perforation Effect on Hydraulic Fracturing Under Triaxial Stresses Using Physical Modeling

Document Type : Research Article

Authors

1 Dept. of Mining, Sahand University of Technology, Tabriz, Iran

2 Dept. of Mining, Isfahan University of Technology, Iran

10.29252/anm.2019.10976.1369

Abstract

Summary
Hydraulic fracturing is one of the most important methods for the propagation of oil and gas reservoirs, which is used to increase the inflow to well bore in low permeability formations. Various parameters such as in-situ stress field, joints and natural fractures of the formation, the fluid rheology, the mechanical properties of the formation, injection fluid flow and perforation affect the hydraulic fracturing pressure. In this research, a triaxial machine was designed and built for experimental investigation of the hydraulic fracturing in conditions close to the field conditions, so that all three of the main stresses in field conditions are applied in laboratory tests. Then, the influence of different perforation parameters such as perforation geometry (including length, diameter and shape), phase of perforation (in both vertical and horizontal wells) and minimum horizontal stress in the presence of perforation, using 38 artificial specimens (plaster + sand) with dimensions of 10×10×10 cm, was considered on the geometry and breakdown pressure, pressure-time diagram, and the development of micro-cracks. The results showed that increasing the perforation diameter, changing the perforation angle to the maximum horizontal stress and increasing the minimum horizontal stress in the case of reverse fault, rises the breakdown pressure.
 
Introduction
Hydraulic fracturing is a stimulation technique used in oil and gas wells to increase the inflow to well bore in low permeability formations. Various parameters such as in-situ stress field, joints and natural fractures of the formation, the fluid rheology, the mechanical properties of the formation, injection fluid flow and perforation affect the hydraulic fracturing pressure. Currently, more than half of the USA oil and gas wells are not able to produce without the use of hydraulic fracturing technology. Many researchers have studied hydraulic fracturing behavior of rocks since decades ago. The researches have showed that hydraulic fracturing operations increase the production of oil wells by up to 30 percent and increase gas wells by 90 percent.
 
Methodology and Approaches
In this research, a triaxial machine was designed and built for the experimental study of hydraulic fracturing and to apply in-situ stresses with different values. This machine has the ability to apply anisotropic stresses in laboratory scale. Abaqus software was utilized to design the machine in terms of stability against the applied stresses. Then, using physical modeling, 38 samples with dimensions of 10×10×10 cm including plaster and sand were constructed and the influence of different perforation parameters such as perforation geometry (including length, diameter and shape), phase of perforation (in both vertical and horizontal wells) and minimum horizontal stress in the presence of perforation on hydraulic fracturing operations were investigated. Finally, the breakdown pressure, hydraulic fracturing geometry, pressure-time diagram and the development of micro-cracks were studied.
 
Results and Conclusions
The results of this study showed that increasing the perforation diameter, changing the perforation angle to the maximum horizontal stress and increasing the minimum horizontal stress in the case of reverse fault, rises the breakdown pressure. Also, the increase of the perforation length and its geometry have not significant effect on the breakdown pressure. Additionally, the change in the perforation angle and the minimum horizontal stress relative to the change in the perforation geometry, including length, diameter, and shape, have more effect on the breakdown pressure and changing the perforation angle relative to changing the in-situ stress in the horizontal well bore is more effective on the breakdown pressure.

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Full Text

شکست هیدرولیکی[i]، یکی از مهم­ترین روش­ها برای تحریک مخازن نفت و گاز با نفوذپذیری پایین است. این روش برای افزایش بهره­وری در مخازن ماسه سنگی با ضخامت کم و همچنین مخازن شیلی با نفوذپذیری و تخلخل مؤثر پایین، کاربرد زیادی دارد[1]. در حال حاضر، بیش از نیمی از چاه­های نفت و گاز آمریکا، بدون بهره‌گیری از فناوری شکست هیدرولیکی قادر به تولید نیستند. امروزه در منطقه آمریکای شمالی، در حدود 58 درصد از چاه‌های گازی و 38 درصد از چاه‌های نفتی، از شکستگی‌های مصنوعی برای تحریک مخازن نفت و گاز استفاده می‌شود. استفاده از تکنولوژی شکست هیدرولیکی در چاه‌های ذکر شده، باعث افزایش دو تا پنج برابری تولید شده است. تحقیقات انجام شده نشان داده است که عملیات شکست هیدرولیکی، تولید چاه‌های نفتی را تا 30 درصد و چاه‌های گازی را تا 90 درصد افزایش می دهد[2].


[i] Hydraulic Fracturing

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Journal of Analytical and Numerical Methods in Mining Engineering
Volume 9, Issue 20
October 2019
Pages 89-104

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History

  • Receive Date: 01 December 2018
  • Revise Date: 23 June 2019
  • Accept Date: 23 June 2019

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