Carbon Dioxide (CO2) Miscible Flooding in Tight Oil Reservoirs: A Case Study

Abstract

Abstract The CO2 flooding is a proven enhanced oil recovery technique to obtain high oil recovery from complicated formations and can be applied to various types of oil reservoirs. It can be injected as immiscible or miscible flooding but immiscible flooding is less effective than miscible flooding. Two types of miscibility can occur: first contact miscibility and multiple contact miscibility. First contact miscibility happens when a single phase is formed when CO2 is mixed with the crude oil. Multiple contact miscibility occurs when miscible conditions are developed in situ, through composition alteration of the CO2 or crude oil as CO2 moves through the reservoir. The miscible flooding process involves complex phase behavior, which depends on the temperature, pressure and fluid properties of the oil reservoir. The CO2 increases oil recovery by oil swelling, reduction of oil viscosity and density, the acidization of carbonate formations and miscibility effects. Multiple-contact miscibility between the injected CO2 and oil can be achieved at pressures above the minimum miscibility pressure (MMP). MMP is the pressure at which the reservoir fluid develops miscibility with CO2 and is a very important parameter in a well-designed CO2 flood project. Some reservoirs are considered tight because of poor rock or fluid characteristics. The main objective of this study is to investigate the performance of CO2 miscible flooding in tight oil reservoirs. This includes determination of minimum miscibility pressure (MMP) involving carbon dioxide and crude oil and miscible CO2 core flooding. This paper addresses the results of CO2 miscible flooding applied to a known reservoir. Several CO2 miscible flooding experiments were conducted using live oil at reservoir temperature and pressure above the MMP on composite cores of known reservoir. The MMP was determined experimentally using the slim tube. High oil recovery from these experiments indicates that the MMP determined from slim tube studies was correct and such a high recovery is only possible if full miscibility occurs during the displacement. The analytical correlation also gave a MMP consistent with MMP determined from slim tube experiments. Introduction Certain reservoirs have been classified "tight" at the time of their discovery, simply because of poor reservoir characteristics. The exploitation of these reservoirs was judged uneconomical at that time because of their low production rate. In fact, the decision whether to produce or not from a reservoir that has been judged "tight" depends not only on the economical context at the time this decision is taken but also on the state of technology prevalent at the time of this decision. It is natural that any change in the price of oil, or any breakthrough in technology especially in drilling, production engineering and enhanced oil recovery can affect significantly the feasibility of developing these tight reservoirs. Reservoirs that have been judged tight on the basis of thirty year old technology may become economical when modern recovery techniques are applied. Both the economical context and the state of new technologies in the domain of enhanced oil recovery, drilling and production engineering have a significant effect on the feasibility of developing these reservoirs.