Low Permeability Gas Reservoir Production Using Large Hydraulic Fractures

There has been relatively little work published on recovering hydrocarbon gas from published on recovering hydrocarbon gas from low permeability reservoirs. Recently several nuclear projects have explored the feasibility of creating a cavity and a fractured zone in such a formation to stimulate production. One such test, Gasbuggy, was begun Dec. 10, 1967, with the detonation of a 26-kt nuclear device in the Pictured Cliffs formation, Rio Arriba Co., N. M. This paper presents a study of stimulating low permeability reservoirs by the creation of long hydraulic fractures. A two-dimensional, two-phase numerical model was used. The reservoir properties of the model approximated those published for the Pictured Cliffs formation. The situations simulated were both vertical and horizontal fractures extending up to 3,000 ft from the producing well. Also, a model simulating a nuclear cavity was designed. This model simulated a well containing an 80-ft radius cavity with a fractured zone of 100 times the reservoir permeability, extending 200 ft past the cavity. The situation simulated was for production with a constant wellbore pressure. Production rate and cumulative gas produced were monitored as functions of time. From these parameters an economic evaluation of each system was prepared. The results of this study showed that all fractures of greater than 1,000-ft radius had greater productivity and greater cumulative gas productivity and greater cumulative gas produced than did the nuclear cavity. It produced than did the nuclear cavity. It appears that large hydraulic fractures may provide an economic means of producing gas from provide an economic means of producing gas from very low permeability reservoirs. Introduction There are large quantities of known hydrocarbons in place that are not being produced because the formation containing the produced because the formation containing the oil or gas has a permeability too low to allow economic production rates. In order to produce this type reservoir, some form of stimulation is required. There has been relatively little information published on the stimulation of low permeability reservoirs. In the past few permeability reservoirs. In the past few years, some projects have been conducted concerning the application of contained nuclear explosions for increasing the productivity in tight formations. The purpose of nuclear stimulation has been to create a large cavity with a radial fractured zone extending past the cavity, or in effect increasing the radius of the wellbore. Another stimulation method is hydraulic fracturing. The purpose of fracturing is usually to improve the formation capacity near the wellbore, offsetting the damage that occurred while drilling. However, another use of fractures presented by L. E. Wilsey provided the basis for this work. provided the basis for this work.