Enhanced Recovery From Naturally Fractured Gas Reservoirs With Seismic Vibrations

Abstract

Water level rising in fracture networks of a naturally fractured gas reservoir is extremely challenging and can significantly decrease the ultimate recovery due to reservoir heterogeneity. Although capillary drainage and gravity force can enhance the displacement of gas recovery from matrix to fracture, these forces may not be so effective in mobilizing large amount of trapped gas through matrix. So called, the use of seismic wave can be suggested as a low cost and environmentally friendly enhanced method compared to the other conventional enhanced methods. This article is aimed to examine the ability of seismic vibration in generating an efficient driving force for moving the remaining gas into the fracture which, to the best of author's knowledge, has not been reported so far. To this end, an in-house numerical simulator has been developed to investigate this enhanced recovery method and also to evaluate the effect of wave characteristics as well as rock properties on the ultimate recovery. The governing equations are solved numerically using finite difference approach and the accuracy of these equations was compared with a commercial simulator for verification. The results are very encouraging and show substantial gas recovery enhancement by applying seismic waves. Our investigation also shows that this stimulation method is more efficient at lower frequencies and also in higher permeable matrix and fractures.

A study on the characteristics of seismic wave propagation in fractured marlstone reservoirs based on mechanical principles

“…When there is gas in the pores, the frequency dispersion and attenuation are the least obvious, and the speed dispersion and attenuation are only found in a very high frequency range; when there is oil, the medium has the most serious dispersion and attenuation, and the salt water comes next. Finally, the influence of the fracture density on the phase velocity and anisotropy parameters of the equivalent medium is analyzed, and it is found that the increase of the fracture density increases the dispersion and attenuation of the medium speed, the difference between the high and low frequency limits is large, and the increase of the medium to the opposite side (Zare et al 2020). Marlstones with higher shale content are not easy to form fractures, while pure marlstones are easy to form effective fractures under stress.…”