A new procedure for the analysis of wellbores drilled in fractured rocks

Sliding along a fractured plane is a normal phenomenon of failure that have been reported during oil and gas wellbores drilling. A new approach has been adopted by Rock Engineering System (RES) to study the interrelationship between various parameters involved in an engineering project. In this approach the main parameters are arranged along the diagonal elements of a matrix called interaction matrix and the interrelation between each pair of parameters are identified in off-diagonal elements. The purpose of this thesis is to evaluate and analyse the sliding mechanism along a fracture plane, which intersects a wellbore during drilling operations by identify interrelationships between different parameters, effectively contributing in this failure to occur in fractured rocks, and also to understand the overall reaction between these parameters that affect the system and be affected by the system to a certain extent. In this a new approach the main parameters such as effective stress, dip and dip direction, aperture of fracture, roughness, pore pressure and density of drilling mud have been arranged along the diagonal elements of the matrix and interrelation between each pair of parameters are identified in off-diagonal elements. The interaction's matrix was quantified using a semi-quantitative expert (ESQ) coding system for assessment of each parameter in the system to be built, also each parameter has been studied in the system by plotting the parameters in cause- effect diagram intensity and dominance of interaction. The results that obtain from a new approach for (20) samples will be compared with the results from Mohr–Coulomb to confirm the validity of a new approach developed based on (RES), this will help to find a better understanding and evaluation to sliding potential of a fracture intersecting a wellbore to avoid or mitigate fractured sliding during drilling operation. To estimate (JRC) joint roughness coefficient, (JCS) joint compressive strength and (ϕ’r) residual friction angle for fracture rocks we have proposed Barton criterion.