Optimization of hydraylic fracturing of tight gas formations in horizontal wells

The discoveries of significant resources of oil and gas in the Barnett, Bakken, Marcellus, and other shale formations have presented an opportunity for national petroleum independence and possible export in the relatively near future. These formations are considered to be "unconventional" resources because of the extremely low formation permeability. This means that traditional oil and gas recovery mechanisms are not economical in these formations. With the development of methods for performing multiple hydraulic fractures in horizontally drilled wells in reasonable periods of time economic production of these formations has been seen throughout the world. However, little is known about the optimal spacing of these fractures in horizontal wellbores - how close together should they be to optimize the net present value (balancing costs of drilling, stimulation and production with future revenue). This paper outlines current hydraulic fracturing propagation theory and describes fracture interaction phenomena such as fractures linking-up or one set of fractures inhibiting the growth of others. This leads to insights related to hydraulic fracture spacing. The optimization of hydraulic fracturing spacing was simulated using mShaleTM from Baker Hughes. It was discovered however that the interference of multiple fractures in a defined zone can be modeled with the mShale software package and it serves as a good pseudo design estimation of optimum fracture spacing.