Fracturing has become a viable and important option for completing horizontal wells. There are many fracturing processes and methods to consider for placement fractures. Optimization of the completion process including the number and size of fractures is still a challenge.
Although fundamentally similar to fracturing vertical wells, horizontal well fracturing has unique aspects that require special attention to ensure successful treatment. Differences exist between horizontal and vertical wells in the areas of rock mechanics, reservoir engineering, and operations. These aspects affect the optimization process for successful placement of treatments and optimum asset performance.
In this paper we discuss the various factors crucial to successful completion of a fractured horizontal well. We discuss these factors in relation to both longitudinal and transverse fracture applications. Success factors include the optimum perforation process, overcoming fluid flow convergence towards the wellbore in case of a transverse fracture, and the fluid flow and stress interference between multiple fractures.
The paper presents a field case and laboratory and numerical experimentations illustrating the impact of the various factors on the completion of the horizontal wells and the optimization of the fracturing process.
Fracturing is no longer restricted to vertical wells drilled in hard formations with very-low permeability. Higher permeability, softer formations as wells as horizontal wells are now routinely fractured. This has led to the importance of examining all reservoir aspects to reach a better understanding of efficient fracture design and eventually the optimization of the well completion. This should include the theoretical and operational parameters influencing the completion of a well. Fluid flow and geomechanical aspects of fracturing a well cannot be ignored when multiple fractures are created. This is especially true in case of fracturing horizontal wells.
Although unstimulated horizontal wells have been very successful in naturally fractured reservoirs and in reservoirs with gas- or water-coning problems, there are many situations where fracturing a horizontal well to improve production capability is a viable or necessary option. The orientation of a hydraulic fracture, with respect to the wellbore, is directly related to the wellbore azimuth with respect to the in-situ stress field. Therefore, 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 possibility of low productivity from an unstimulated well.
It should also be remembered that fracturing a horizontal well may dictate which direction the well should be drilled and how it should be completed. Fracturing a horizontal well does not necessarily mean that the well has to be cased and cemented. There are many cases of fracturing horizontal wells in openhole or uncemented liners. The field example within this paper discusses one of these cases. Fracturing a horizontal well may be considered when one of the following situations is apparent.
Restricted vertical flow caused by low vertical permeability or lamination.
Low formation productivity because of low formation permeability.
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 because the fracture would grow in height as well as length.