Since its introduction in the late 1980's, fracturing of horizontal wells has become a viable completion option. In certain reservoir conditions, horizontal wells offer significant production improvement over vertical wells, however, to maximize their return on investment, it may be necessary to fracture horizontal wells. This is especially true in case of tight gas formations.
This paper reviews the technology developed in the area of fracturing horizontal wells. The paper includes discussion on the rock mechanics, the operational, and the reservoir engineering aspects of fracturing horizontal wells.
The rock mechanics discussion reviews the various theoretical and experimental work that has been done in the area of fracturing horizontal wells. It also reviews the various phenomena such as creation of transverse and longitudinal fractures, creation of multiple fractures, and fracture reorientation among others that are associated with creation of a fractured horizontal well. Stability of the horizontal well as it relates to stimulation is also discussed.
The reservoir engineering portion of the paper discusses the production performance and testing aspects of a fractured horizontal well. Emphasis is given to fracturing tight gas formations, since this area is the one in which this technique is considered to be the most effective. The performance of a longitudinal fracture is examined and compared to a fractured vertical well and to the more popular transverse fractured horizontal well.
Because performance of a longitudinal fracture is similar to that of a fractured vertical well, the existing solutions for fractured vertical wells may be applied to longitudinal fractures. This approximation is valid for moderate to high dimensionless conductivity. In the case of transverse fractures, the outer fractures outperform the inner fractures. However, for most cases, more than two fractures are necessary to efficiently produce the reservoir.
Operational aspects of fracturing horizontal wells for both transverse or longitudinal fractures are discussed, and advantages and disadvantages of each type will be outlined. Examples and case histories are discussed. The paper also presents guidelines for stimulation of a horizontal well and includes both propped and acidized fracturing as well as matrix acidizing.