A Mechanistic Model for Relative Permeability of Gas and Water Flow in Hydrate‐Bearing Porous Media With Capillarity

Abstract

Lack of mechanistic models to describe petrophysical properties of mobile phases in gas hydrate‐bearing sediments is one of the key challenges in accurately predicting gas production. The major drawback of empirical models that are used to fit a relative permeability curve for mobile phases in gas hydrate‐bearing sediments is that they are based on experimental data, which are limited, and not able to account for hydrate morphology in pore space. This study proposes a relative permeability model that is mechanistic in nature and developed to account capillarity by building on the original nonempirical relative permeability model that assumes negligible capillary pressure. The proposed model implicitly accounts for capillarity with the help of four empirical parameters (two for each mobile phase) that incorporate each mobile phase pressure. It is shown that the proposed model provides an improved match to relative permeability data (derived from pore‐scale simulation of gas hydrate‐bearing sediments) than nonempirical relative permeability by accounting for the effect of capillary pressure. Additionally, unlike fully empirical models that can predict relative permeabilities reliably only at gas hydrate saturations for which experimental data are available, the proposed model only requires fitting the empirical parameters once with experimental data at any single gas hydrate saturation and then it can then be used to predict relative permeability at any gas hydrate saturation. The mechanistic nature of the proposed model allows studying relative permeability of hydrate‐bearing sediments as a function of hydrate morphology and wettability (fluid phase distribution) besides other physical parameters of the model (e.g., porosity, gas, and water residual saturation). Based on the sensitivity analysis of different hydrate morphologies on gas/water relative permeability, it is found that gas relative permeability is sensitive to hydrate morphologies, while water relative permeability shows little dependency on hydrate localization in pore space.

A Novel Relative Permeability Model for Gas and Water Flow in Hydrate-Bearing Sediments With Laboratory and Field-Scale Application

“…To overcome the lack of experimental relative permeability data for gas hydrate, we recently proposed a mechanistic model 19,20 for hydrate-bearing media that is based on physics and predicts relative permeability without the need for calibrations at various S h . Although this mechanistic model 19,20 can overcome the need for calibrations at various S h , it may be computationally more expensive to use in a reservoir simulator than existing empirical models.…”

“…To overcome the lack of experimental relative permeability data for gas hydrate, we recently proposed a mechanistic model 19,20 for hydrate-bearing media that is based on physics and predicts relative permeability without the need for calibrations at various S h . Although this mechanistic model 19,20 can overcome the need for calibrations at various S h , it may be computationally more expensive to use in a reservoir simulator than existing empirical models. The model proposed in this study, while overcoming the need for calibrations at various S h , is expected to be computationally less expensive than mechanistic model 19,20 and additionally it can account for heterogeneity in pore-sizes that is not possible using the mechanistic model.…”

“…Although this mechanistic model 19,20 can overcome the need for calibrations at various S h , it may be computationally more expensive to use in a reservoir simulator than existing empirical models. The model proposed in this study, while overcoming the need for calibrations at various S h , is expected to be computationally less expensive than mechanistic model 19,20 and additionally it can account for heterogeneity in pore-sizes that is not possible using the mechanistic model. This study proposes a novel relative permeability model developed specifically for hydrate-bearing porous media with multiphase flow of gas and water.…”

“…1(a) implies that gas hydrate is already formed in porous media and continuous gas production leads to hydrate decomposition. Further discussion related to the distribution of fluids around gas hydrates and its effect on relative permeability can be found in our recent works 19,20 .…”

Maximum Sizes of Fluid-Occupied Pores within Hydrate-Bearing Porous Media Composed of Different Host Particles

“…Hydraulic properties of hydrate-bearing sediments are quite crucial [10][11][12], and they still represent an ongoing research issue although great effort has been made [13][14][15][16].…”