Optimum mud window prediction is very crucial for drilling any well. Accurate prediction of pore pressure, fracture pressure and other geomechanical parameters such as stresses, rock mechanical properties and finally the collapse pressure are key for designing the optimum mud window and effective well planning. Predrill predictions of pore pressure and wellbore stability become more and more challenging as the industry is moving to more and deeper and ultra-deep water wells. This is primarily becaue of lack of offset calibration together with inherent probrems and challenges associated with deep water environments. A substantial amount of nonproductive time (NPT) was associated during the initial phases of drilling campaigns in the Brunei deepwater. Accurate mud weight window prediction using regional scale pore pressure prediction and geomechanical modeling clearly demonstrated a significant reduction in nonproductive times over the different phases of drilling campaigns till date. This also includes a regular update or refinement of the model as soon as new data or information becomes available. This paper presents some of the methodologies employed during well planning and construction with refinement along the way, resulting in improvement on pore pressure and geomechanical model. Our intent is to document and share our experiences and lessons learnt in Brunei deepwater well so that design and execution workflow can be continuously improved thus the well can be delivered safely and costeffectively.