Date of Graduation

2012

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Petroleum and Natural Gas Engineering

Committee Chair

H. Ilkin Bilgesu

Committee Member

Samuel Ameri

Committee Member

Khashayar Aminian

Abstract

The purpose of this thesis was to investigate the wellbore integrity for horizontal shale gas wells using geomechanical properties of shale gas reservoirs to better predict rock behavior, more specifically the maximum stress around the wellbore. Real reservoir properties were used to construct a hypothetical model. A single horizontal well was utilized to analyze the rock behavior. Because we are looking to analyze the geomechanics of the reservoir, two models must be constructed. A reservoir model was first built and then coupled with a more precise geomechanic model. The base model, without any hydraulic fracturing or other stimulation treatments, was constructed and calibrated. However, because shale gas wells generally need stimulation treatments to be economic, a hydraulic fracture was introduced into the model. Once this took place, different parameters of the hydraulic fracture were varied and the results of the geomechanic model analyzed. Two different geomechanical models were used, the Mohr Coulomb and Drucker-Prager models, and analyzed. Once all of the models were completed, analysis began to compare the variation in the hydraulic fracture parameters and also the difference between the two geomechanical models. The maximum stress around the wellbore was affected by two major events, the reservoir depletion through production and the hydraulic fracture. The stress created in the wellbore during the short term is due to the hydraulic fracture and can account for up to half of the total stress during the life of the well. Wells that had shorter hydraulic fracture half-lengths had greater stress at the beginning of production, while wells with longer fracture half-lengths had greater stress in the long term due to the increased production due to the longer half-length. The stress created in the long term life of the reservoir is due to production, with increased production leading to increased stress in the wellbore. Increased fracture permeability leads to more production and therefore, more stress. Furthermore, if the wellbore does not fail during the first year of production after hydraulic fracturing, most likely it will not fail during the life of the well.

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