Parametric Investigation of Shale Gas Production Considering Nano-Scale Pore Size Distribution, Formation Factor, and Non-Darcy Flow Mechanisms

Abstract

The effects of the parameters involved in shale gas reservoir simulation are investigated using an improved transport equation for description of gas flow in nano-Darcy permeability media. This approach takes into account the effects of molecular collisions at the pore wall and is valid in all flow regimes: Darcy, slip, transition, and free-molecular flow. The study generalizes a transport equation valid for all flow regimes for an ideal gas in a capillary tube and extends the formulation to quantify the effect of a distribution of pore sizes for different flow regimes. We first describe the adopted methodology to model ideal gas transport and then account for real gas behavior by modifying the conventional definition of the mean free-path. The relationship of this approach to the Klinkenberg correction for slip flow and other published formulations that are described as the sum of a Darcy term plus a diffusive transport term are examined. An application of the present approach and its implications are demonstrated by means of a numerical example involving a hydraulically-fractured shale gas reservoir producing at a constant rate. The bottomhole pressure predictions from the non-Darcy formulation indicate a substantial deviation from the bottomhole pressure predicted by assuming Darcy flow and consequently, can be expected to have serious implications for production forecasting and planning for well abandonment. In particular, for infinite acting flow regimes that are commonly observed for shale gas wells, our calculations indicate that flowing bottomhole pressures tend to be higher than those calculated using a transport formulation governed by Darcy's law, thereby describing the potential for significantly enhanced productive well life.

Gas Transport Model in Organic Shale Nanopores Considering Langmuir Slip Conditions and Diffusion: Pore Confinement, Real Gas, and Geomechanical Effects

“…The calculated results from different models are shown in Figure 8 (corresponding parameters used for comparison are presented in Table 5). The model of Michel et al [73] describes only bulk phase gas transport and ignores adsorbed gas. Thus, the results are quite lower than those of other models and basically constant with pressure changes.…”

A Numerical Study of Thermal-Hydraulic-Mechanical Simulation With Application of Thermal Recovery in Fractured Shale-Gas Reservoirs

“…However, in shale reservoirs, the ultrafine pore structure of these rocks can cause violation of the basic assumptions behind Darcy's law. Depending on a combination of pressure-temperature conditions, pore structure and gas properties, Non-Darcy flow mechanisms such as Knudsen diffusion and Gas-Slippage effects will impact the matrix apparent permeability (Fathi et al 2012;Michel et al 2011;Swami et al 2012;Sakhaee-Pour and Bryant, 2012). In addition, constant decreasing pore pressure during production (transient flow and pseudo-steady-state flow) can lead to reduction of thickness in gas adsorption layer and increase in the effective stress, which in turn, can impact the formation matrix microstructure and effective pore radius (Wang and Marongiu-Porcu, 2015).…”

Required Understanding for the Development of Shale Reservoirs in the Middle East in Light of Developments in North America

“…They included two correction terms; one for the viscosity due to pore size and the second one accounts for the effect of collision with pore walls. Villazon et al (2011) studied flow of gas in nano-Darcy permeability media. They considered the effects of molecular collisions at the pore wall and the validity of the model in all flow regimes.…”