Visual Study of Water Injection in Low Permeable Sandstone
Authors: Sun W. , Tang G.Q. 
Published: March 2010

Abstract
Visual micro-model technology has been applied to investigate multiphase flow in porous media because it allows watching the fluid flow clearly with a microscope. However, most micromodels employed are made up of glass media. A sandstone micro-model (SMM) manufactured directly from thin sandstone chips is introduced and applied in this study of water injection in low permeable rock. The main advantage for this kind of micromodel is that it retains the original pore structure, clays, cements, and pore surface properties. A total of 18 sandstone micro-models with permeability from 1 - 10 md are used for displacement tests at room temperature.
Results show that the water injection in the weakly oil-wet to neutral-wet low permeable sandstone micro-model is dominated by the injection pressure. At low injection pressure, the water can only enter large pores that have good conductivity. A large number of pores are not flooded by water. When the injection pressure is increased, water is forced into some small pores to drive oil out. In addition, heterogeneous properties of the porous media always cause a bypass flow resulting in early water breakthrough and poor water displacement efficiency. We also found that oil recovery is directly proportional to the permeability of the model, suggesting that pore conductivity is the key to waterflood efficiency in low permeable rock.

Introduction
Glass micro-models (GMM) have been implemented to investigate multiphase flow in porous media at a pore-sized level. The most important advantage employing glass micro-models is its transparent feature that allows the study of multiphase flow in the pore structures with the help of a microscope. Two types of glass micro-models, hypothetical and duplicated, have been used so far. A hypothetical micro-model is produced based on the rock parameters such as throat size, pore body size, and coordinate number. Therefore, such models have a fixed ratio of throat to pore body and the pore structure is very simple. For most cases, the pore structures are repeated. The most popular hypothetical glass micromodel is the network model. The duplicated micro-model is based on a real pore structure that is obtained from a thin section image and reproduced. The pore structure is copied onto a glass plate that is then subjected to an image-etching process using a chemical solution. Compared to the formal model, the latter one has more complicated pore structures.
Research applications with visual micro-models include:heavy oil solution gas drive(1–3);gas and water injection and immiscible two-phase flow(4–9); and,enhanced oil recovery(10, 11).
Visual micro-model technology has so far provided useful experimental evidence at pore-level and assumes certain hypotheses on aspects of reservoir engineering. However, the application of visual micro-models still has limitations. The most important one is that the glass porous medium is totally different from real rock. Therefore, to restore the initial properties of the selected rock is very difficult.
In this work, we present an innovative sandstone micro-model (SMM) which is manufactured from a sandstone chip directly.