Optimum Mud Overbalance and ROP Limits for Managing Wellbore Stability in Horizontal Wells in a Carbonate Gas Reservoir

larger stress contrast across the wellbore resulting from the overburden (S v) and difficulties with drilling in the maximum horizontal stress (S Hmax ) direction under the prevailing strike slip stress conditions in the field 1 . Several data sets, including open hole logs, were integrated through geomechanical analy ses 2 to develop a mechanical earth model (MEM) providing magnitudes of the three principal in situ stresses, the azimuth of S Hmax direction, pore pressure and the rock strength proper ties along the logged open hole section. Horizontal in situ stresses can be calculated using a poroelastic horizontal strain model 3 and further calibrated by the observed wellbore wall failure; the result is continuous profiles of stress magnitudes along the well trajectory, Fig. 1. Apart from pore pressure, the magnitudes of horizontal Saudi Aramco has been drilling horizontal and multilateral wells to develop gas fields. Due to a production-induced drop in reservoir pressures, along with the tight nature of the reser voir rock, development activities have focused more on placing new wells, completed with multistage hydraulic fracturing, to ward the minimum horizontal stress (S Hmin ) direction with the goal to improve lateral reservoir contact, which enables higher production at sustained rates, thereby increasing recovery while drilling fewer wells. Horizontal wells drilled in the S Hmin direction are made more challenging by complex geological conditions and com pressional in situ stress conditions. The data shows that some wells were drilled without major difficulty while other wells encountered more problems, leading to stuck pipe events. A detailed study was conducted to identify the nature of these problems and ascertain major controlling factors for this variable drilling experience. The goal was to make future operations safer and more efficient through recommendations based on a diagnostic analysis of the observed problems in existing wells. Analysis of data suggests that excessive borehole breakouts and a faster rate of penetration (ROP) are the key contributing factors to the observed drilling challenges. In addition, differ ential sticking has been found to be a potential risk across high porosity and/or depleted zones. As a result, determining the optimum mud weight for a given well based on a pre-drill geo mechanics model was recommended to manage the hole stability. In addition, a safe limit for the ROP, set as a function of hole azimuth, was identified to manage efficient hole cleaning and avoid stuck pipe issues due to pack off. The recommendations made based on this analysis enabled successful drilling and timely completion of several horizontal wells across the field.