The Potential of Carbon Dioxide Gas Injection Application in Improving Oil Recovery

Abstract

Abstract Carbon dioxide (CO2) gas could increase oil recovery by means of swelling, evaporating and lowering oil viscosity. In the displacement front, injected gas may become enriched by the oil components and gas may dissolve into the reservoir oil. By assuming that local thermodynamic equilibrium is occurring at the oil-gas interface, the phase behavior can be calculated by the equation of state. The displacement process can be modeled by a set of differential equations, called the mass balance equations, which can be written for each component in the reservoir oil and the CO2 gas injected. The linear velocity component in the mass balance equation is expressed by Darcy's law for oil and gas phase flow, which comprise oil and gas permeability, oil and gas viscosity and pressure gradient terms. A set of the flow equation then solved numerically by the use of a one dimensional compositional simulator. The simulator has been validated by analytical methods, which is based on the method of characteristics. In this study, we want to see the potential of CO2 injection application in improving oil recovery by simulating a slim tube experiments. CO2 gas is available in large quantity in the Natuna Sea and some place in Kalimantan, Indonesia. The benefit of the study is that we could predict the recovery efficiency of CO2 gas injection in the field by combining the results here with the macroscopic areal sweep and invasion efficiencies obtained from other models or simulations. And, the potential application of the study is that we could have a good estimate of the recovery improvement under CO2 gas injection, which will be the basic input parameters for the economic feasibility study and also a decision can then be made whether to implement or abandon the prospective project. Introduction Carbon dioxide gas as an injection fluid into oil reservoirs has been a recognized well and tested as Enhanced Oil Recovery (EOR) method, because CO2 dissolves easily into oil, it reduces oil viscosity, and it can extract the light components in oil at sufficiently high pressure, and it can become miscible with oil at very low pressure. However, before a further decision be made on whether to apply it in field or not, generally some laboratory experiments need to be done, one of them being a series of slim tube experiments. The experiments on slim tube will indicate the microscopic efficiency of the injection process. They need to be combined with the macroscopic sweep efficiency and invasion efficiency obtained from the reservoir characterization, to have an overall injection efficiency of the process. Since experiments on slim tube at high pressures are costly, time consuming and prone to experimental failures, it is of great interest to simulate those experiments with a numerical simulator. With a numerical simulator, besides the economic and time benefits, we could also calculate results on certain conditions, which otherwise would have never been possible with experiments due to technical constraints. The injection pressures and temperatures applications of CO2 injection could vary from low, intermediate up to high. The phase behavior of oil and CO2 gas and the transfer of components between oil and gas, based on the assumption that thermodynamic equilibrium always occur at the oil-gas front, can be described with adequate accuracy by equations-of-states for real gases, which were introduced by van der Waals. CO2 gas in large amount has been discovered in theXC-08 reservoir, Natuna Sea, Indonesia, co-existing with commercial methane gas. Since CO2 gas is an unfriendly substance from environmental perspective, the problem arised as how to separate, remove the CO2 gas from the methane, and to dispose it at a safe place somewhere. It is more interesting economically, however, to make use of the produced CO2 as far as possible. One of the alternatives is to use the produced CO2 gas as an injection fluid in the nearby fields. Many injection schemes using CO2 have been applied for the oil wells, including CO2 gas continuous injection, CO2 gas slug followed by water, CO2 gas or liquid slug followed by alternate water and CO2 gas injection (WAG), CO2 - surfactant foam slug followed by water injection and carbonated water injection.