Wellbore instability has been the primary cause of financial losses in boreholes in the drilling industry. Wellbore instabilities are responsible for 10–20% of the total drilling cost. It has been estimated that wellbore instability causes an annual economic loss of ﹩ 1 - 6billion in the oil industry across the world. One type of these wellbore instabilities was a hole enlargement problem encountered in the J-NC186 Oil field located in southern of Libya. This paper examines one side to solve this problem. So a geomechanical wellbore stability analysis was implemented using Schlumberger Techlog software to effectively plan the future drilling operations in the field to maximize the drilling margin for the future wells drilled, and to optimize the future field development. 1-D geomechanical models show that the horizontal wells are more stable than the vertical ones. The models also show that drilling to the orientation of east-west can minimize the wellbore instabilities. The models suggested the optimum mud weight window to drilling the reservoir section safely, and represented the results using stereographic projection. The outcomes of this study can be utilized for further field developments for enhancement of the hydrocarbon production (e.g. hydraulic fracturing, open-hole completions, and enhanced hydrocarbon recovery).
Wellbore stability is a term used in the Oil and gas industry to describe usable condition of the borehole during drilling operations. A usable hole must successfully accommodate logging or any open-hole evaluation, casing run and any other drilling activities.
The Oil and gas industry continues to fight borehole problems. The problems include: hole collapse, tight holes, stuck pipes, poor hole cleaning, hole enlargement, plastic flow, fracture, and lost circulation. Most of these borehole problems that drive up drilling costs are related to wellbore stability. These problems are mainly caused by the imbalance created between the rock strengths and induced stresses after wellbore drilling.