Multiphase Compositional Modeling in Small-Scale Pores of Unconventional Shale Reservoirs

Abstract

Compositional modeling of hydraulically stimulated naturally fractured liquid-rich shale (LRS) reservoirs is a complex process that is yet to be understood. The flow and multiphase mass transfer in the nano-, meso-, and macro-scale pores, as in Eagle Ford, Woodford and Bakken is of great interest. Understanding the production mechanisms from such reservoirs is crucial in the overall effort to increase the ultimate hydrocarbon production. Thus, we focused on deciphering the physical fundamentals of various recovery mechanisms via reservoir modeling. The starting point was examining the phase behavior issues in unconventional reservoirs. Specifically, we constructed phase diagrams using a new correlation to shift the critical properties of components in the nano and meso-scale pores. The correlation was applied to three recently published Eagle Ford fluid samples. The new phase behavior correlation was used in a dual-permeability compositional model to determine the nature of pore-to-pore flow and, eventually, the hydrocarbon production from wells. In the simulation models we allowed for the phase behavior differences between fracture and matrix and included a multi-level flow hierarchy from matrix (nano, meso, and macropores) to fractures and finally to the well. To make computation accurate we resorted to a series of detailed logarithmic local grid refinement (LS-LGR) in various strategic subdomains in the matrix and fracture.As a result of this modeling study, we have concluded several reasons why hydrocarbon fluids can move in the shale reservoir nano, meso, and macro-scale pores and why we are able to produce from such low-permeability reservoirs. For instance, favorable phase envelope shift of hydrocarbon mixtures in the nano-and meso-scale pores is one of the contributing factors to economic production in gas-condensate and bubble-point systems. Also noted, when the phase envelope is crossed in gascondensate systems, a large gas-to-oil volume split in the nano, meso, and macro-pores plays a crucial role in hydrocarbon recovery during depletion. For the bubble-point oil region, the low viscosity of the liquid phase and the delay in gas bubble evolution appears as the main reason for favorable oil production. Furthermore, 'rubblizing' the reservoir in the vicinity of hydraulic fractures creates another favorable environment for improved drainage, which is why multi-stage hydraulic fracturing is so critical in successful development of shale reservoirs.

Phase Behavior and Minimum Miscibility Pressure in Nanopores

“…Zarragoicoechea and Kuz (2004) modeled the reduction of critical temperature by applying the van der Waals model and reported a good match of their model and the experimental data by Morishige et al (1997). 3 (Bird et al 2007). 1), in which r LJ can be calculated from the bulk critical properties with Eq.…”

Compositional Modeling of Enhanced Hydrocarbons Recovery for Fractured Shale Gas-Condensate Reservoirs with the Effects of Capillary Pressure and Multicomponent Mechanisms

“…We assume that the phase behaviour can be described by bulk-phase thermodynamics (using conventional EOS), which is a reasonable assumption for pores larger than about 10 nm. Note that in recent years, a large number of studies in the literature employed the shifted critical temperature and pressure from Singh et al (2009) in the conventional EOS to describe fluid phase behaviour in nanopores (Devegowda et al 2012;Alharthy et al 2013;Jin et al 2013). However, for pore sizes smaller than 10 nm, strong fluid/surface interactions result in a heterogeneous density distribution in the pores.…”

“…Many studies indicate that the thermodynamic phase behavior of in-situ hydrocarbon mixtures in confined spaces significantly deviates from that of bulk fluids in the PVT cells (Wang et al 2013;Jin et al 2013;Alharthy et al 2013;Teklu et al 2014;Wang et al 2014;Jin and Firoozabadi 2015;Rezaveisi et al 2015;Xiong et al 2015;Tan and Piri 2015). The nanopores in the ultra-tight shale formation could lead to significant interfacial curvature and capillary pressure between confined vapor and liquid phases.…”

Numerical Study of Production Mechanisms in Unconventional Liquid-Rich Shale Volatile Oil Reservoirs

“…The phase behavior in nano pores is strongly influenced by capillary effects, electrostatics and van der Waals forces (Teklu et al, 2013;Nojabaei et al, 2013). In confined conditions, interaction between hydrocarbon molecules and pore walls is elevated, which changes the physical properties of bulk fluids as measured in the lab, such as critical pressure and temperature, viscosity, interfacial tension (IFT), and density.…”