Analysis of vertical, horizontal and deviated wellbores stability by analytical and numerical methods

Journal of Petroleum Exploration and Production Technology, Jan 2014

Wellbore stability problems are known to cost the oil and gas industry billions of dollars each year. However, these costs can be significantly reduced through the application of comprehensive geomechanical models. This paper is relevant and is appropriate in the oil and gas industry. The objective of this paper is the comparison of four rock failure criteria, named the Mohr–Coulomb, Mogi–Coulomb, Modified Lade and Tresca yield criterion and to apply them to determine the optimum drilling direction and mud pressure. The stability models has been applied to a well located in Iran oil field and leads to easily computed expression for the critical mud pressure required to maintain wellbore stability. Then the finite difference method was used to show the validation and accuracy of predicted mud pressure and investigate the wellbore stability in different states of vertical, horizontal and deviated. The results showed that the Mohr–Coulomb and Tresca criteria estimate the highest minimum mud pressure required for wellbore stability while the Mogi–Coulomb and the Modified Lade criteria estimate the lowest minimum mud pressure. Nevertheless, the mud pressures predicted by all these four criteria are acceptable and can be used.

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Analysis of vertical, horizontal and deviated wellbores stability by analytical and numerical methods

Abbas Khaksar Manshad 0 1 2 H. Jalalifar 0 1 2 M. Aslannejad 0 1 2 0 M. Aslannejad Department of Chemical and Petroleum Engineering, Persian Gulf University , Boushehr, Iran 1 H. Jalalifar Department of Chemical and Petroleum Engineering, Shahid Bahonar University , Kerman, Iran 2 A. K. Manshad (&) Department of Petroleum Engineering, Abadan Faculty of Petroleum Engineering, Petroleum University of Technology , Abadan, Iran Wellbore stability problems are known to cost the oil and gas industry billions of dollars each year. However, these costs can be significantly reduced through the application of comprehensive geomechanical models. This paper is relevant and is appropriate in the oil and gas industry. The objective of this paper is the comparison of four rock failure criteria, named the Mohr-Coulomb, MogiCoulomb, Modified Lade and Tresca yield criterion and to apply them to determine the optimum drilling direction and mud pressure. The stability models has been applied to a well located in Iran oil field and leads to easily computed expression for the critical mud pressure required to maintain wellbore stability. Then the finite difference method was used to show the validation and accuracy of predicted mud pressure and investigate the wellbore stability in different states of vertical, horizontal and deviated. The results showed that the Mohr-Coulomb and Tresca criteria estimate the highest minimum mud pressure required for wellbore stability while the Mogi-Coulomb and the Modified Lade criteria estimate the lowest minimum mud pressure. Nevertheless, the mud pressures predicted by all these four criteria are acceptable and can be used. - Investigation of wellbore stability and advising a sensible plan before drilling require identification of problematic regions and improving of drilling operation. The two important elements needed in a wellbore stability model are the failure criterion and the constitutive behavior model. Wellbore drilling in a formation causes stress alteration around the borehole due to removal of rock. This stress alteration is important, since it leads to an increase in stress around the wall of the hole, therefore the induced stresses should be adjusted by choosing proper mud pressure to stabilize wellbore. Although the selection of an appropriate rock failure criterion for analyzing wellbore stability is difficult and controversial (Al-Ajmi and Zimmerman 2009; Mclean and Addis 1990), a number of rock failure criteria and behavior models have been accomplished for the diagnosis and prediction of wellbore instability. Since there is no single criterion suitable for all materials and situations, drilling engineers should be able to choose a suitable rock failure criterion based on formation rock properties to predict an optimum mud pressure to stabilize wellbore. Bradley (1979) was the first to model for compressive wellbore failure of a deviated well for the purpose of proposing proper mud weights to preclude borehole failure. However, he did all of his analyses for the rare case where the two horizontal stresses are equal and less than the vertical stress. Ewy (1999) found that the modified Lade criterion predicts critical mud weight values that are less conservative than those predicted by the MohrCoulomb criterion yet are not as unconservative as those predicted by the DruckerPrager criterion. Al. Ajmi and Zimmerman (Al-Ajmi and Zimmerman 2004) introduced the fully polyaxial MogiCoulomb failure criterion, and then proposed a new 3D analytical model (2006) to approximate the mud weight needed to avoid failure for the vertical wells based on MogiCoulomb failure mechanism coupled with elastic theory. Their study shows the significant role of intermediate principle stress in rock strength, where using three dimensional MogiCoulomb failure criterion greater mud weight windows than MohrCoulomb failure mechanism have been obtained. Zhang et al. (2010) examined five failure criteria on various rock specimens to determine the best criterion for the wellbore stability analysis. Therefore, they concluded that the 3D HoekBrown and the MogiCoulomb criteria are appropriate for wellbore stability analysis. On the other hand, numerical modeling methods provide an excellent opportunity to analyze the wellbore state of stress for different applications such as wellbore drilling, wellbore design or hydraulic fracturing (Lee et al. 2011). McLean and Addis (1994) used finite element methods to predict wellbore stability parameters. Chatterjee and Mukhopadhyay (2003) used ANSYS finite element software and investigated stress around a wellbore to study the effects of fluid pressure during drilling. Hoang et al. (2004) investigated wellbore stability in multilateral junctions using finite element method and showed that orientation of junction and in situ stresses both have significant impact on well completion and stability. Wang and Sterling (2007) performed numerical analyses named finite elemen (...truncated)


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Abbas Khaksar Manshad, H. Jalalifar, M. Aslannejad. Analysis of vertical, horizontal and deviated wellbores stability by analytical and numerical methods, Journal of Petroleum Exploration and Production Technology, 2014, pp. 359-369, Volume 4, Issue 4, DOI: 10.1007/s13202-014-0100-7