A DRILLABILITY AND GEOMECHANICAL WELBORE STABILITY ANALYSIS FOR OPTIMAL BIT SELECTION - CASE STUDY OF A FIELD IN NIGER DELTA

This paper establishs the importance of hard streak in bit selection. The hard streak is associated with siliceous - ferruginous sandstone with traces of siltstone rapped in augen of shale. Hitherto the drilling industry is disturbed with challenges of optimal bit selection due to a fact that current bit models in market are bias to very hard Formation like hard streak. In Soku Oil field of Niger Delta in Nigeria, West Coast of Africa, there exits challenges on proper bit to drill the section of this hard Formation. This segment of Formation is called drillers’ nightmare because it affects every inch of drilling ? from the bit in the drilling string to drilling tools, mud, hole diameter and general rig operation. Most of the current models were propagated by experiements without reference to field practical imput. Engineers that specialize in drill bit optimization, including Directional Drillers, possess the analytical skill to evalua te the drilling problems in a methodical fashion, carefully considering the larger context of the drilling process. Therefore, to tackle the menace of the hard streak, great experience, mineralogical investigation of the streak, regrouping and remodelling of existing models were done. Data for this study were gathered through personal observation as a Directional Driller at Soku field and operators in Niger Delta. They were subjected to analytical methods, presented in tables, figures and charts. Based on t he data analysis, the findings of this study are that: ? Insert bits are perfectly good to drill all sections of hard streak provided rotation at bottom is not more than 36 hours, less cones are lost. ? Use of PDC bits to drill or ream through the hard strea k is an aberration while insert bit (447) is the best for drilling hard streak. ? Regrouping of International Association of Drilling Companies (IADC) Code and remodelling of current models in the market were inevitable to accommodate selection of hard str eak bits. ? Use of steerable motor all through a hard streak to reduce axial lateral vibration on drilling string is recommended.