Abstract
The drilling of an oil well in an area of geological complexity presents many challenges in the planning and drilling phases. These complexities included a highly-deviated well profile, dipping formations, and naturally fractured formations. Moreover, the wellbore challenges were compounded by the high stresses in a tectonically-active area. Thus, to help ensure successes of drilling operation, it is necessary to incorporate new technologies to define the risk that the drilling case presented and to prepare for the potential problems predicted in the pre-well planning. Geomechanical modeling for wellbore stability can address the different conditions that constitute this type of well. However, in order to quantify the effect of the variables mentioned above (drilling parallel to bedding planes in a shale formation and drilling through a naturally fractured formation), it is necessary to have fracture porosity and permeability data, fluid viscosity inside the fractures, poroelastic parameters like undrained Poisson, Biot coeffient to model the weak bedding effect, and strength parameters like cohesion and the friction angle of the bedding planes and bedding plane orientation that account for the angle of attack analysis (angle between the well and the bedding plane) (Aadnoy et.al 2009). This paper analyzes the bedding plane failure which is base on the linear elastic and isotropic model for stresses around the wellbore, with the aim of trying to understand the general behavior of inclined boreholes due to anisotropy using the several case studies. The analysis remarkably found that for a laminated rock (sand/shale stringers), a weakness of a plane may subject the well toward collapse for the hole angles between 10 to 40deg (Aadnoy and Chenevert 1987). The model also analyzes the 3D effect of attack angle with changing azimuth for a constant inclination on bedding plane exposed horizontal wells. It is seen that bedding exposed does not only depends on inclination but also on the dip of the formation, attack angle and well azimuth. The model also categorized geomechanical operational scenarios into three while drilling complex weak bedded horizontal wells, and this include pre - drilling (pore pressure prediction, mechanical properties, and stresses), while drilling (real - time monitoring at the rig site to obtain geomechanical properties from petrophysical logs), and Post - drilling (logs, and offset events documented). Finally, the model results defines the optimized well path, integral mudweight envelope (geomechanical window), wellbore diagnosis and also ensure whether the horizontal well data has existed on the bedding exposed or protected positions. All these will help in reducing NPT (non productive time) wellbore instability related stuck pipe incident.
