Application of Anisotropic Wellbore Stability Model and Unconventional Fracture Model for Lateral Landing and Wellbore Trajectory Optimization: A Case Study of Shale Gas in Jingmen Area, China
Authors: Wang Weixu , Wen Heng , Jiang Pei , Zhang Pengwei , Zhang Lei , Xian Chenggang , Li Junjun , Zhao Chunduan , Li Qingshan , Xie Qinghui 
Published: April 2019

Abstract
The shale gas in Jingmen area in China has unique features different from North America shale plays, such as abundant natural fracture corridors with complex patterns and distributions, formed through multiple tectonics in geological history, high in-situ stresses with extreme variations of heterogeneities and anisotropies, and highly laminated rocks. Wells drilled in this area are often less stable than comparable wells drilled into non-laminated rocks. Hydraulic fracturing has encountered many difficulties, such as high treating pressure, difficulty in proppant placement, constrained fracture height and complex fracture geometry. It has been recognized that optimizing lateral landing and wellbore trajectory is essential to reduce operation risks and improve productivities.
An integrated 3D shared earth model was constructed with 0.5-m vertical resolution of the targeted sweet section to capture vertical heterogeneities measured from logs through integrating seismic, geological structure, log, and core data. This model includes anisotropic mechanical properties, in-situ stress field, and multiscale natural fracture systems. Near borehole induced stress was computed accounting formation anisotropies, and wellbore shear failure mechanism was modeled by a modified Plane of Weakness (PoW) model. The model can predict the extent of failure region around the wellbore and then provide mud weight window for safe and effective drilling. The fracturing simulations were performed with Unconventional Fracture Model (UFM) that models the hydraulic fracturing process in complex formations with pre-existing natural fractures including interaction with natural fractures and between hydraulic fracture branches (i.e., stress shadow effects). Numerical reservoir simulations were computed to forecast productivities of different lateral landing and well trajectory designs and provide optimal strategy.
A comprehensive integrated workflow was generated from drilling to production through stimulation to optimize well planning. This study proposed the best interval L111 for lateral placement and optimal well trajectory along NE23° for wellbore stability and hydraulic fracturing effectiveness to reduce operation risks and ahicheve highest productivities considering unevenly well-developed natural fractures, significant heterogenetic and anisotropic in-situ stress, Guanyinqiao limestone formation and highly laminated rock.
This integrated workflow represents the comprehensive multidisciplinary approach to coupling geophysics, geology, petrophysics, geomechanics, wellbore stability, complex hydraulic fracture propagation, and production simulation models aimed towards optimizing lateral landing and well trajectory. The implementation of this workflow guides drilling, stimulation and development of shale gas reservoirs in the most optimized and scientific way.