Immiscible and Miscible Gas-Oil Gravity Drainage in Naturally Fractured Reservoirs

Abstract

In the phase of declining oilfields and at a time when recovering hydrocarbons has becoming more difficult, effective techniques are the key to extract more oil from mature fields. The difficulty of developing effective techniques is often the real obstacle when dealing with heterogeneous formations such as naturally fractured reservoirs, which are among the most challenging class of hydrocarbon formations. Because of the large degree of heterogeneity, in terms of reservoir properties, the production methods from naturally fractured reservoirs differ from the production methods from conventional reservoirs. To identify an efficient and optimum strategy for oil production from naturally fractured reservoirs, fluid displacement mechanisms at reservoir conditions need to be understood. Gas injection into the conventional reservoirs has been already common practice for years. However, gas injection into naturally fractured reservoirs is still controversial. This is mainly due to the existence of highly permeable fracture systems in fractured reservoirs. These highly permeable and interconnected fracture networks offer easy-flow pathways to the injected gas. As a result, the injected gas is usually produced without sufficient contact with the oil in the matrix, which is left behind and unproduced. Therefore, it is of practical importance to examine the efficiency of a gas injection process in naturally fractured reservoirs to achieve a reliable and effective production process. This thesis is a collection of experimental and theoretical work on the efficiency of gas-oil gravity drainage process in naturally fractured reservoirs. Gas injection experiments were performed using a modified experimental set-up to simulate the gravity-drainage process in naturally fractured reservoirs. In this thesis, the possibilities and limitations of improved oil recovery from fractured reservoirs by gas injection are investigated.