Thousands of wells are hydraulically fractured in the Appalachian Basin each year with little clear understanding of what the resulting fracture actually looks like. A number of variables exist in the subsurface including natural fractures, permeability variations, in-situ stresses, faults, etc. that can influence the ultimate dimensions and orientation of the created fracture. It is necessary that the stimulation design team understand the impacts that these features can have on the path a hydraulic fracture takes in the subsurface. The created fracture and its conductivity ultimately dictate a well's productivity and drainage area.
This paper will outline the basics of how in-situ stresses affect the orientation of propagating hydraulic fractures and how some geological characteristics can impact the process. Some discussion will be presented on the current technologies being used to understand fracture geometry. These include microseismic imaging and tiltmeter surveys.
The vast majority of Appalachian Basin reservoirs require some type of stimulation to be economically viable. Many thousands of wells have been drilled and completed utilizing a variety of stimulation techniques. Both the reservoir and the created fracture are, by their nature, difficult to see and assess with any real certainty. It is therefore necessary to make assumptions about how the geology of the reservoir will respond to the style of stimulation in order to optimize the recovery of hydrocarbons. Over the years some principal assumptions have been accepted that influence the hydraulic fracture design for the majority of treatments. Some of these assumptions were controversial at first but have gainedgeneral acceptance over time. Other design factors are the result of "local" conclusions based on the results of treatments that have been refined through years of modification.