An Improved Multicomponent Diffusion Model for Compositional Simulation of Fractured Unconventional Reservoirs

Abstract

Summary Most simulators currently use the advection/diffusion model (ADM), where the total flux comprises Darcian advection and Fickian diffusion. However, significant errors can arise, especially for modeling diffusion processes in fractured unconventional reservoirs, if diffusion is modeled by the conventional Fick’s law using molar concentration. Hence, we propose an improved multicomponent diffusion model for fractured reservoirs to better quantify the multiphase multicomponent transport across the fracture/matrix interface. We first give a modified formulation of the Maxwell-Stefan (MS) equation to model the multicomponent diffusion driven by the chemical potential gradients. A physics-based modification is proposed for the ADM in fractured reservoirs, where fracture, matrix, and their interface are represented by three different yet interconnected flow domains to honor the flux continuity at the fracture/matrix interface. The added interface using a more representative fluid saturation and composition of the interface can hence better capture the transient mass fluxes between fracture and matrix. The proposed approach is also implemented in an in-house compositional simulator. The multicomponent diffusion model is validated with both intraphase and interphase diffusion experiments. Then, the improved model for fracture/matrix interaction is compared with a fine-grid model. The proposed multiple interacting continua (MINC) model with three continua (MINC3) can better match the fine-grid model’s result than the double-porosity (DP) model, which only obtains a fair match at an early time. Then, we simulate a gas huff ‘n’ puff (HnP) well in the Permian Basin to investigate the effect of diffusion within the fractured tight oil reservoir. The simulation reveals that diffusion has a minor effect on the performance of depletion when oil is the dominant phase. For gas HnP, the simulation neglecting diffusion will underestimate the oil recovery factor (RF) but overestimate the gas rate. The DP approach tends to overestimate the RF of heavy components but leads to a similar cumulative oil RF compared with MINC3. With the diffusion included in the simulation, gas HnP performance becomes more sensitive to the soaking time than the model without diffusion. Although increasing the soaking time will lead to a higher RF after considering diffusion, the incremental oil is not sufficiently large to justify a prolonged soaking time.

An efficient 3D cell-based discrete fracture-matrix flow model for digitally captured fracture networks

“…Numerical methods are fundamental tools for studying fluid flow in fractured porous media and have been widely applied in petroleum and mining engineering (Adachi et al 2007 ; Chen et al 2022 ; Sun et al 2023 ; Tian et al 2021 ). Significant efforts have been made to develop appropriate models to simulate fluid flow in fractured porous media since the 1960s, including (1) the equivalent continuum model (ECM) (Huang et al 2013 ; Sheng et al 2020 ; Wu and Qin 2009 ); (2) dual-continuum model (DCM) (Azom and Farzam 2012 ; Barenblatt et al 1960 ; Gerke and van Genuchten 1993 ); (3) discrete fracture-matrix model (DFM) (Hoteit and Firoozabadi 2008 ; Karimi-Fard et al 2004 ; Zhao et al 2019b ) and (4) embedded discrete fracture model (EDFM) (Li and Lee 2008 ; Moinfar et al 2013 ; Shakiba et al 2018 ).…”

Modeling Microscale Foam Propagation in a Heterogeneous Grain-Based Pore Network with the Pore-Filling Event Network Method

“…In the foam flooding application, foaming gas and foaming surfactant solution are injected to generate foam in the reservoir. The presence of foam can significantly reduce the mobility of displacing fluids and provide favorable profile control, which eventually improves the sweep efficiency of the immiscible displacement process [4][5][6].…”

CO2 Viscosification for Mobility Alteration in Improved Oil Recovery and CO2 Sequestration

“…A multicomponent diffusion model [24] was used to calculate the diffusive fluxes. The formulation used in this work is based on the chemical potential gradient.…”