Abstract
Although unstimulated horizontal wells have been very successful in naturally fractured reservoirs and in reservoirs with gas or water coning problems, there are certain situations where fracturing a horizontal well may be a viable option. Because of the dependence of fracture orientation on well direction with respect to the stress field, the possibility of fracturing a horizontal well must be considered before the well is drilled. The appropriate contingency plans should be made to anticipate the possible low production from an unstimulated well. It should be remembered that fracturing a horizontal well may also dictate how the wellbore may be completed and/or oriented. Fracturing a horizontal well may take place in one of the following situations.
Restricted vertical flow caused by low vertical permeability or the presence of shale streaks
Low formation productivity due to low formation permeability
The presence of natural fractures in a direction different from that of induced fractures. Thus Induced fractures have a high chance of intercepting the natural fractures, or
Low stress contrast between the pay zone and the surrounding layers. In this case, a large fracturing treatment of a vertical well would not be an acceptable option since the fracture would grow in height as well as length. Drilling a horizontal well and creating either several transverse or longitudinal fractures would allow rapid depletion of the reservoir through the fracture(s).
Although fundamentally similar to fracturing vertical wells, fracturing horizontal has its unique aspects that require very special attention to secure successful treatment. Differences between horizontal and vertical wells exist in areas of rock mechanics, reservoir engineering, and operational aspects. To start with, the basic rock mechanics aspects are examined.
