In this paper, directional wellbore stability analysis is carried out for the shales in which weak bedding planes are developed. Shale layers in Northeastern British Columbia area has been selected for the wellbore stability analysis due to well-known geological and geomechanical properties. In the case of shale layer with weak bedding planes, it was found that breakouts around the wellbore developed asymmetrically. It was also found that wellbore is more stable with the trajectory almost perpendicular to the weak bedding planes. In this case, less mud weight can be applied to achieve more stable directional wellbore with this trajectory. It is expected that the methodologies and results in this paper can be beneficial to wellbore stability analyses for shale layers with similar geological and geomechanical setting to this research area.

Directional and horizontal drilling has become very important technologies in developing unconventional resources commercially. Directional steering techniques which enabled directional and horizontal drilling have been evolved continuously. In 1990s', bottom hole mud motor and RSS(rotary steerable system) were introduced to deal with very complex drilling trajectory and extended reach drilling for unconventional resources. Recently, PRSS and Hybrid RSS are used for horizontal drilling operation. These advancements in directional steering technique enabled drillers to drill extended reach well of several kilometers, and also vitalized shale gas and oil developments in North America. In this study, mechanical theory and advantages/disadvantages of various directional steering techniques have been examined along with their development history. And also we presented several considerations which could be made when each directional steering technique being used.

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The ratio of fractured reservoir is very high in oil & gas fields around the world. The demand of drilling technology for fractured reservoir is expected to increase continuously if oil and gas prices are economical. The purpose of the review study is to help operator or driller in selecting of proper drilling technology for preventing a lost circulation in the fractured formation. In order to achieve this goal, fractured reservoir(formation) they are classified into partial lost circulation formation and total lost circulation formation. In case of partial lost circulation formation, the drilling problem can be solved by using LCM(lost circulation material) mud additive and squeezing cement. For shallow depth, total lost circulation formation can be drilled safely and economically with casing drilling method. Also, for deeper depth, problems of total lost circulation in formation can be solved by applying mud cap, which is one of the drilling methods. This was confirmed through field application such as Italy's Medusa-1 field and Qatar's North field.