Integrating micro-scale modelling with core measurements to improve natural gas production in shale gas reservoirs

Abstract

Prior to 2008, shale gas reservoirs were deemed uneconomical to produce. Hydraulic fracturing and horizontal drilling have shifted this perspective, reducing the flow resistance from the reservoir to the well. Notwithstanding the thousands of shale gas wells currently actively producing around the world, factors controlling the permeability and flow behaviour in shale gas formations are still incompletely understood. A profound understanding of the flow processes manifesting in shale gas reservoirs will contribute to more effective Enhanced Gas Recovery (EGR) schemes, ultimate recovery and accurate gas production forecasting.Owing to the micro- and nano-size of pores, transport in shale rocks depends on the pore size and predominantly on pore geometry and tortuosity. To gain new insights into the mechanics of gas production from shale formations, we constructed a geometrically accurate model from an actual shale scanning electron microscope micro-image. Taking into account the pertinent rock and gas parameters (e.g., porosity, permeability, viscosity, etc.) we have determined the gas flowrate, the pressure variations and deduced the production rate at the micro-level.A non-dimensionalisation methodology was developed which permits the comparison between micro-scale modelling results with actual core measurements several orders of magnitude larger in spatial scale. Normalised micro-scale modelling results compare well with actual core data shedding light on some of the most important aspects which govern gas flow: geometry, pressure gradient, compressibility, and permeability. Moreover, the cumulative gas production for different gases was shown to improve with an increase in the molecular mass of the gases. Ultimately, our efforts aim to tie theoretical understanding with experimental observations deemed significant for boosting the productivity of gas from shale formations.