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Geomechanics and Engineering
  Volume 7, Number 3, September 2014 , pages 233-246

A new geomechanical approach to investigate the role of in-situ stresses and pore pressure on hydraulic fracture pressure profile in vertical and horizontal oil wells
Seyed Erfan Saberhosseini, Reza Keshavarzi and Kaveh Ahangari

    Estimation of fracture initiation pressure is one of the most difficult technical challenges in hydraulic fracturing treatment of vertical or horizontal oil wells. In this study, the influence of in-situ stresses and pore pressure values on fracture initiation pressure and its profile in vertical and horizontal oil wells in a normal stress regime have been investigated. Cohesive elements with traction-separation law (XFEM-based cohesive law) are used for simulating the fracturing process in a fluid-solid coupling finite element model. The maximum nominal stress criterion is selected for initiation of damage in the cohesive elements. The stress intensity factors are verified for both XFEM-based cohesive law and analytical solution to show the validation of the cohesive law in fracture modeling where the compared results are in a very good agreement with less than 1% error. The results showed that, generally by increasing the difference between the maximum and minimum horizontal stress, the fracture pressure and its profile has been strongly changed in the vertical wells. Also, it\'s been clearly observed that in a horizontal well drilled in the direction of minimum horizontal stress, the values of fracture pressure have been significantly affected by the difference between overburden pressure and maximum horizontal stress. Additionally, increasing pore pressure from under-pressure regime to over-pressure state has made a considerable fall on fracture pressure in both vertical and horizontal oil wells.
Key Words
    hydraulic fracturing; in-situ stress; pore pressure; fracture pressure profile; cohesive elements; finite element; XFEM-based cohesive law
(1) Seyed Erfan Saberhosseini:
Department of Petroleum Engineering, Science and research branch, Islamic Azad University, Tehran, Iran;
(2) Reza Keshavarzi:
Young Researchers and Elites Club, Science and Research Branch, Islamic Azad University, Tehran, Iran;
(3) Kaveh Ahangari:
Department of Mining Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran.

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