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====Wellbore Stability Analysis (Optimizing Well Placement)====

====Wellbore Stability Analysis (Optimizing Well Placement)====

In fields operated by ONGC in India, the horizontal stress orientations were determined using logging tools to help optimize the trajectory of future wells in any fault system (Tiwari, 2013). [[:File:GeoWikiWriteOff2021-Tayyib-Figure21.png|Figure 21]] summarizes the different fault systems in which wells can be drilled. In a normally faulted system, the preferred drilling direction for inclined or horizontal wells is the minimum horizontal stress direction. The resulting wellbore tends to be more stable, thus requires lower mud weight and lower cost. Whereas, in a strike-slip or thrust fault system, the preferred drilling direction for inclined or horizontal wells is the direction of the maximum horizontal stress.

In fields operated by ONGC in India, the horizontal stress orientations were determined using logging tools to help optimize the trajectory of future wells in any fault system<ref>Tiwari, R., 2013, Recognizing horizontal stress orientation for optimizing well placement and well completion jobs: SPG 10th Biennial International Conference and Exposition, Kochi, India, November 23-25, 2013, 5 p. </ref>. [[:File:GeoWikiWriteOff2021-Tayyib-Figure21.png|Figure 21]] summarizes the different fault systems in which wells can be drilled. In a normally faulted system, the preferred drilling direction for inclined or horizontal wells is the minimum horizontal stress direction. The resulting wellbore tends to be more stable, thus requires lower mud weight and lower cost. Whereas, in a strike-slip or thrust fault system, the preferred drilling direction for inclined or horizontal wells is the direction of the maximum horizontal stress.

[[File:GeoWikiWriteOff2021-Tayyib-Figure21.png|center|framed|{{Figure number|21}}Different types of fault systems due to in-situ stresses (from Zhang<ref name=Zhang />).]]

[[File:GeoWikiWriteOff2021-Tayyib-Figure21.png|center|framed|{{Figure number|21}}Different types of fault systems due to in-situ stresses (from Zhang<ref name=Zhang />).]]

* Pei, Q., X. Ding, B. Lu, Y. Zhang, S. Huang, and Z. Dong, 2016, An improved method for estimating in situ stress in an elastic rock mass and its engineering application: Open Geosciences, vol. 8, no. 1., p. 523-526, doi:10.1515/geo-2016-0047.

* Pei, Q., X. Ding, B. Lu, Y. Zhang, S. Huang, and Z. Dong, 2016, An improved method for estimating in situ stress in an elastic rock mass and its engineering application: Open Geosciences, vol. 8, no. 1., p. 523-526, doi:10.1515/geo-2016-0047.

* Teraghi, K., and F. E. Richart, 1952, Stresses in rock about cavities: Geotechnique, vol. 3, no. 2, p. 57–90.  

* Teraghi, K., and F. E. Richart, 1952, Stresses in rock about cavities: Geotechnique, vol. 3, no. 2, p. 57–90.  

* Zhang, J., 2019, Applied petroleum geomechanics: Amsterdam, Netherlands, Elsevier, 534 p.

* Zhang, J., 2019, Applied petroleum geomechanics: Amsterdam, Netherlands, Elsevier, 534 p.

* Zhang, Y., S. Yin, and J. Zhang, 2021, In situ stress prediction in subsurface rocks: An overview and a new method: Geofluids, vol. 2021, 11 p.

* Zhang, Y., S. Yin, and J. Zhang, 2021, In situ stress prediction in subsurface rocks: An overview and a new method: Geofluids, vol. 2021, 11 p.