Optimization of Microbial Flooding in Carbonate Reservoirs

Abstract

Abstract Up to date, several investigators have studied the possibility of using microorganism in improving oil recovery, but little work has been reported regarding optimization of the process. In the laboratory, bacteria have been shown to produce chemicals such as surfactant, acids, solvents, polymers, and gases (mainly CO2) that can significantly contribute to improving displacement and sweep efficiency. Some of these microorganisms can withstand the harsh environment of the oil field and grow at a substantial rate feeding on the organic matter and crude oil itself, thus leading to improvement of oil recovery. Moreover, the MEOR process is friendly to the environment. Several field trials have been reported that showed the potential of bacterial enhanced oil recovery (BEOR) in improving oil recovery. Because these microorganisms are living organism and their behavior is difficult to predict, therefore no attempt has been made to study the parameters that control the process performance. This has become the main objective of this work. In this work, we investigate the field parameters that affect the design a new process of Microbial Enhanced Oil Recovery in order to achieve optimum oil recovery. In order to reach this goal, the reservoir engineering factors that affect the recovery efficiency are defined first. These field parameters considered the most relevant and chosen for this study are the injected bacteria concentration, the adaptation time, the optimum slug size of bacteria solution,a and the process application time. The capability of the microbes to transmit through a heterogeneous system and in long cores, and the effect of bacteria on rock wettability are also investigated. Introduction A number of literature reviews have been published on effect of microorganism on enhanced oil recovery (Smith &Collins1, Zajic &Donalison2, Moses &Springham3, Bryant &Douglas4 and Bryant &Burchfield5). Single well treatment is the most widely used technique to clean the area around the wellbore and improve oil recovery. In this technique, the well is stimulated through the injection of a small amount of bacteria solution and kept closed for a certain amount of time (number of hours depending on bacteria adaptation time) before placing the well back on production. This is process is relatively inexpensive and quick response could be obtained. Another method is to inject the microorganism with water at a certain concentration of cells/ml with a small amount of nutrient. Actually, both techniques can be implemented with minor modification to existing field facilities. A number of projects were conducted utilizing microorganism to improve oil recovery (Streeb and Brown6, Lazar et al.7, Bryant, R.S. et al.8, Dietrich et al.9, Portwood10, Bryant et al.11, Ratliff et al.12, Jenneman et al.13, Dietrich et al.14, Yonebayashi15 and Maure16) where improvement in the oil recovery was reported. In laboratory, microbes have been reported to produces chemicals such as surfactant, acids, solvents, (ketones and alcohol's), polymer and gases (CO2)17–21 that can improve the oil recovery substantially over water flooding. The main objective of this work is to experimentally evaluate the effects of different parameters on the overall microbial recovery efficiency. The parameters investigated in this project were the adaptation time, the slug size, the timing of the process (secondary versus tertiary), and the concentration of microbes. In addition, the capability of microbial species to transmit through a heterogeneous system and in long cores was also investigated.