**3. Multi-fracture network fracturing**

Since it was proposed for the first time by Giger in 1985 [8], the concept of horizontal well fracturing has been widely practiced as a valuable technique to improve well production and increase the recovery of unconventional reservoirs. Horizontal well fracturing treatments in field generally create multi-fractures in selected intervals along the wellbore. Processes of fracture initiation and propagation in horizontal wells are different from those in vertical wells due to the larger contact surface area with the formations, thus resembling more complex reservoir situation. When multi-fractures are propagated, they often join or intersect with each other, forming patterns that are known as multi-fracture networks, which immensely increase the storage capacity and the fluid transmissibility of formations. Multi-fracture networks are not easy to be assessed or studied due to the complexity; however, they are evaluated using mathematical and statistical techniques and may be represented using fractals.
