Borehole instability while drilling operations in most of formations is a continuing problem that results in substantial annual expenditure for the petroleum industry ($1.3 billion according to some estimates). The technical problems of shale instability are closely associated with majority properties of shales such as, strength and deformation. Other features, like temperature, formation pressure, open wellbore exposure time, interval length of open wellbore, tectonics, etc., can directly impact drilling operations. Drilling a borehole into a formation of different rocks in equilibrium medium makes stress application in the region of the borehole. In circumstances where the stresses significantly exceed the strength the subsequent inequality can cause borehole destabilization.
The proposal prospect is located in the southern part of Meleiha Development Lease. The main target of the prospect is to verify the hydrocarbon potential of the Cretaceous sandstone reservoirs, belonging to the Bahariya, and A.E.B. Mbr. The oil and gas bearing reservoir of the A.E.B Mbr. has been proven in some of the wells already drilled within Meleiha Development Lease with some recent successful discoveries in A.E.B. Mbr.
A drilling fluid exposure related interaction might occur because parameters such as chemical potential, ionic application, etc., of the drilling fluid and the shale formation fluid are not in equilibrium. Changes in these factors may vary near wellbore formation pressure that will influence the wellbore stress-case and shale state strength and thereby affect the stress-strength balance.
An effective drilling process, the interrelated factors, should be included into well planning, mud system selection criteria and/or new mud development. The presented idea here shows the influence of these considerations on wellbore stability.
A detailed case study is introduced where methodologies have led to achievements and where the experiences have been transferred into new drilling fluid developments. Results described here are for developing a comprehensive approach borehole instability resolution so helping to deliver better managing of borehole instability issues in the field.
The developed model is effective for expecting areas of borehole instability. The mitigation of wellbore instability can be achieved by adjusting the adequate mud weight with the proper selection criteria of the drilling fluid characteristics. However, in some cases, the modification in wellbore trajectory is insufficient and mud weight must be adjusted as well. The developed borehole instability model is potentially applicable to other field cases using a same approach which could be accustomed to the certain field specifications and requirements.