An Experimental and Simulation Investigation on the Effect of Different Gas Mixtures on Performance of Miscible CO2 Injection in HPHT Abu Dhabi Reservoir

Abstract

Abstract The carbon dioxide flood represents one of the proven enhanced oil recovery methods. However, there are significant challenges associated with applying CO2 flood in onshore or offshore reservoirs. One of the common problems is a limited supply of CO2. Therefore, recycling and re-injection of the produced gas should be considered in many applications especially in the case of giant carbonate reservoir in the Middle East. In this work presented here, we performed a comprehensive series of slim-tube and phase-behavior experiments coupled with numerical simulation to explore the effect of the mixture of non- hydrocarbons and hydrocarbon gases with CO2 on the behavior and the performance of the gas flooding process. This study involves a series of slim-tube experiments to identify the MMP of CO2 and different mixture of gases namely N2, C1, and C2. Moreover, mixing cell experiments were also performed to calibrate phase behavior models based on crude oil and injected gas interaction in a PVT cell. Furthermore, full compositional analysis of the produced oil and gas for both slim-tube and phase-behavior experiments were carried out to better understand the dominant mechanism of the injected gas at different conditions. Besides, the experimental results were employed as a benchmark against the numerical 1-D simulations which was based on the tuned EOS with advance PVT experiment's to predict the impact of different mixtures on the MMP. The experimental results of CO2 with a different gas mixture of up to 20% were shown that the attribution of N2 and C1 in increasing the MMP in both dead and live oil systems and N2 has the highest impact on increasing the MMP. The results of the gas chromatography analysis of the produced gas clarified that there was an interaction between the injected gas and the crude oil in which a bank of immiscible light hydrocarbon gases created at the miscible front. The composition of C1 in the produced gas was decreased from 70% at CO2 BT to 31% at the end of the experiment. Therefore, when CO2 recycling was considered, the concentration of CO2 will be decreased, and miscibility between the oil and CO2 required much higher MMP. However, the CO2 extract oil components (C1 up to C30) which contribute to leaving heavier oil behind. The miscibility of remaining oil was achieved but at very high pressure due to the non-existence of light components. The results of 1-D slim-tube simulation have shown a promising result in predicting MMP of the performed experiments. The result of the study demonstrated the potential of lowering the cost by design a mixture of CO2 with hydrocarbons and non-hydrocarbons gases instead of injection high purity CO2. Although, this study contributes to understanding the mechanism of the process of CO2 injection when recycling and reinjection are considered.