Experimental and Modelling Study of Gravity Drainage in a Three-Block System

Hamidreza Erfani,Mohammad Hossein Ghazanfari,Behzad Rostami,Abtin Karimi Malekabadi

doi:10.1007/s11242-020-01521-x

Abstract

Gravity drainage is known as the controlling mechanism of oil recovery in naturally fractured reservoirs. The efficiency of this mechanism is controlled by block-to-block interactions through capillary continuity and/or reinfiltration processes. In this study, at first, several free-fall gravity drainage experiments were conducted on a well-designed three-block apparatus and the role of tilt angle, spacers’ permeability, wettability and effective contact area (representing a different status of the block-to-block interactions between matrix blocks) on the recovery efficiency were investigated. Then, an experimental-based numerical model of free-fall gravity drainage process was developed, validated and used for monitoring the saturation profiles along with the matrix blocks. Results showed that gas wetting condition of horizontal fracture weakens the capillary continuity and in consequence decreases the recovery factor in comparison with the original liquid wetting condition. Moreover, higher spacers’ permeability increases oil recovery at early times, while it decreases the ultimate recovery factor. Tilt angle from the vertical axis decreases recovery factor, due to greater connectivity of matrix blocks to vertical fracture and consequent channelling. Decreasing horizontal fracture aperture decreases recovery at early times but increases the ultimate recovery due to a greater extent of capillary continuity between the adjacent blocks. Well match observed between the numerical model results and the experimental data of oil recovery makes the COMSOL multiphysics model attractive for application in multi-blocks fractured systems considering block-to-block interactions. The findings of this research improve our understanding of the role of different fracture properties on the block-to-block interactions and how they change the ultimate recovery of a multi-block system.

Highlights

The efficiency of the process is controlled by block-to-block interactions such as capillary continuity, which preserves the hydraulic continuity of the oil phase over fractures, and reinfiltration, occurring when the produced oil from a block enters the underneath matrix block due to gravity and/capillary forces (Dullien 2012)
In higher tilt angles the travelling liquid blocks will be transferred easier to the vertical fracture rather than forming liquid bridges in the horizontal fracture
The obtained ultimate recovery factors were in the same range of the obtained experimental data by other researchers (Firoozabadi and Markeset 1992, 1994), while quantitative comparison was avoided because of different set-up configuration, rock and fluid properties

Summary

Introduction

Two-phase flow in fractured rocks is relevant to various application, ranging from geothermal energy (Babaei and Nick 2019; Erfani et al 2019), groundwater contamination (Gleeson et al 2009; Sebben et al 2015; Aminnaji et al 2019; Aljuboori et al 2019; Dejam 2019), carbon capturing and storage (Emami-Meybodi et al 2015; Babaei and Islam 2018; Erfani Gahrooei and Joonaki 2018; Dejam and Hassanzadeh 2018; Erfani et al 2020; An et al 2020b; Ershadnia et al 2020), and soil salinization (Weisbrod and Dragila 2006) to enhanced hydrocarbon recovery (Farajzadeh et al 2012; Rokhforouz and Akhlaghi Amiri 2017; Rokhforouz and Amiri 2018; Bakhshi et al 2018; Rabbani et al 2020a; Chen et al 2020; An et al 2020a). Gravity drainage is a process in which the gravity acts as the main driving mechanism and the non-wetting phase (i.e., gas phase) pushes the oil out of the rock. It is an effective production mechanism in the gas-invaded zone due to a larger density difference. Spontaneous imbibition is usually effective in the water-invaded zone, where water is imbibed into the rock due to capillary forces and oil is produced to the fractures. Free-fall gravity drainage is usually the major oil production mechanism in high permeability and thick reservoirs with a great drawdown pressure (Hagoort 1980; Chatzis and Ayatollahi 1993), while forced gravity drainage is a result of gas injection. The bulk flow regime in the matrix and vertical fractures and, on the other hand, film flow in the horizontal fracture strongly influence the two-phase gas–oil flow in fractured oil reservoirs (Rostami et al 2010)

Objectives

Results

Conclusion