Analysis of Flow of Gas and Water in a Fractured and Non-Fractured Low-Permeability Reservoir Under Production

Abstract

We modified Black Oil Applied Simulation Tool (BOAST) Program for gas Reservoirs, and successfully applied it to simulate production of gas from fractured and non fractured low permeability reservoirs. Our modification results in significant decrease in computational time and storage requirements, and allows us to reduce the designated grid blocks to the size of the fractures. Thus the fractures were only distinguished from the matrix by their physical properties. Pressure and saturation of gas and water were calculated at different locations in the reservoir during the production. Our calculation shows that the coproduction of gas and water and presence of the induced fractures significantly enhance the economical production of gas from low permeability reservoirs. Introduction The oil embargoes of the early seventies, resulted in a continuous interest in the discovering and producing the unconventional resources of oil and gas. The advances in technology and in particular fast growth in supercomputing significantly contributes to the research and development in this field. Among the unconventional resources of gas, tight sand reserves have drawn a significant amount of attention for economical gas recovery using massive hydraulic fracturing. Sharer and O'Shea (1) estimate over 500 trillion cubic feet of natural gas may be recoverable from low permeability sandstones located in the Western and Eastern United States. Although there is a large potential for development of this resources, however significant stimulation is required in the hope of attaining feasible production capability. The use of massive hydraulic fracturing which at present is the most promising technique also produces erratic response from tight sand, particularly in lenticular formations (Spencer,(2). To date, only thick, blanket-type formations have been exploited because only a limited knowledge of reservoir characteristics is necessary to stimulate economic production from these reservoirs. A majority of resource base is associated with more complex blanket sand formations. In these formations, a variety of interdependent parameters, such as the gas recovery rate and active reservoir life, are still uncertain. Without further research of these factors, the full potential of the tight sands resource base will not be realized. These uncertainties can be reduced by identifying parameters critical to production, and models based on this knowledge. Tight gas sands are characterized scopic features such as high capillary low porosity, high irreducible wetting saturation, and low permeability (less 987 × 10(-6) m2). Economic production of gas from the rock matrix generally requires that flow to the well bore be aided by natural or induced fracture systems. However, production rate is still set by the rate of flaw of gas from the matrix into the fracture system. Therefore a knowledge of fluid flow in the matrix is required. Although there are several experimental studies in the literature for flow properties in tight sand such as: Jones and Owens, (3), Randolph (4), Walls et al (5), Freeman and Bush (6), Chowdiah (7), and Soeder (8), however there is a need for more experimental results to determine the behavior of naturally and hydralically fractured tight sand formations. In the literature there are only few studies regarding the theoretical analysis of single and multiphase flow in tight sand formations. P. 157^

Factors controlling prolific gas production from low-permeability sandstone reservoirs: Implications for resource assessment, prospect development, and risk analysis

“…Despite a complex burial history, original depositional fabric continues to exert a strong control on productivity; those rocks that had more favorable porosity and permeability structure during deposition tend to remain the more attractive reservoir targets despite a complex burial and uplift history. Low-permeability reservoirs are characterized by high capillary entry pressures, high irreducible water saturations, low to moderate porosity, and low permeability (e.g., Arastoopout and Chen, 1987;Byrnes, 1997). Table 2 summarizes petrophysical parameters commonly found in many low-permeability gas accumulations in the Rocky Mountain region.…”