Fluid Flow and Microstructural Properties of Gas Shales

Abstract

In recent years, the production of natural gas and oil from shale has had a dramatic impact on the gas and oil industries, with shale gas plays the biggest source of natural gas in, for example, the USA (US Energy Information Administration, 2016). There has been a consequential and considerable increase in demand for better characterization of shale gas plays. However, cost-effective shale gas production requires detailed knowledge of the petrophysical characteristics of the shale from which the gas is extracted. Parameters such as the kerogen fraction, pore size distributions, porosity, permeability, the frackability of the rock and the degree to which natural fracturing already occurs are required in order to be able to estimate potential gas reserves and how easily it can be extracted. Characterization of shale gas plays is challenging because of they tend to be both tight and heterogeneous due to the mechanisms by which they are deposited and subsequent diagenetic processes and also due to the small size of the pores and low permeability, porosity. SEM imaging has confirmed the tremendous physical heterogeneity of shale gas plays ( Charmers et al., 2009; Loucks et al., 2009; Wang et al., 2009; Ambrose et al., 2010; Curtis et al., 2010). Strong characterization of a reservoir necessitates detailed knowledge of, for example, flow capabilities, permeability, porosity, pore connectivity and storage. Knowledge of these characteristics will help to determine flow capacity, how to control gas extraction, and hydrocarbon storage. Permeability and porosity are two principal parameters required for accurate assessment of gas-/oil-in-place to forecast production. The measurement of porosity is considered to be relatively straightforward; numerous tests have been used successfully, including helium porosity. On the other hand, the measurement of permeability is more challenging. For instance, steady-state measurements which have been used successfully with more typical reservoirs are not easy to use with shale samples, for which more complex, unsteady-state methods including pulse-decay are required (Javadpour and Ettehadtavakkoli 2015). Measurement of low permeability’s using pulse-decay is considered a good method for measurement of permeability of shale rock samples (Jones, 1997) but has a number of drawbacks such as being relatively expensive, and results can depend on sample size. Thus, other methods are required for confirmatory analysis of permeability and pore systems in shale rock samples.