Assessment of Enhanced Oil Recovery Efficiency in Mature Fields via Long-Term Core Flooding Tests

Thesis Abstract

Mature oil fields face significant challenges in optimizing hydrocarbon recovery due to declining primary and secondary production, necessitating the evaluation of advanced Enhanced Oil Recovery (EOR) techniques to maximize reservoir productivity and prolong field life. This study aims to empirically assess the efficiency of various EOR methods through long-term core flooding tests, providing quantitative insights into their effectiveness under reservoir-mimicking conditions. The specific objectives include determining the displacement efficiency of polymer flooding, surfactant injection, and thermal recovery; evaluating the impact of core properties on EOR performance; and developing predictive models to estimate recovery outcomes based on core characteristics and flooding parameters. A mixed-method research design integrates experimental laboratory procedures with statistical analysis. The study population comprises core samples obtained from mature fields, with a total of 45 core plugs representing different lithologies—siltstone, sandstone, and shale—classified into three groups for testing. Sampling employed stratified random selection to ensure representative diversity across reservoirs. Data collection involved tightly controlled core flooding experiments conducted over a three-year period, simulating reservoir conditions of pressure, temperature, and salinity. Multiple EOR techniques—polymer flooding, surfactant flooding, and thermal methods—were applied sequentially to each core sample, with displacement efficiency recorded through differential pressure and effluent analysis. Analytical techniques include high-resolution differential pressure transducers, effluent oil and water analysis via gas chromatography, and core wettability assessments through contact angle measurements. Data were processed using regression analysis to establish relationships between core properties and recovery efficiency, and analysis of variance (ANOVA) tested for statistically significant differences among EOR methods across lithologies. Additionally, multivariate statistical models, incorporating principal component analysis (PCA), were developed to identify the most influential factors affecting recovery. The study also references the theory of wettability alteration and flow mechanics to interpret core flooding results, providing a theoretical basis for observed variations in EOR performance. Expected findings suggest that polymer flooding yields the highest incremental recovery in sandstone cores, with an average increment of 15%, whereas surfactant flooding offers moderate improvements of about 8%, predominantly in siltstone. Thermal recovery methods show variable results depending on core lithology, with shale cores exhibiting lower recovery efficiencies due to their low permeability. Crucially, core wettability and porosity significantly influence EOR effectiveness, with more oil-wet, high-porosity cores demonstrating superior displacement efficiency. Predictive models developed from the analysis aim to accurately forecast recovery factors based on core and operational parameters, thereby aiding reservoir management decisions. This research contributes novel empirical data on the performance of different EOR techniques under long-term flooding conditions, filling identified gaps in the literature that predominantly rely on short-term laboratory tests or field-scale pilot studies. The integration of experimental results with statistical modeling advances understanding of the complex interactions between reservoir properties and EOR processes, enabling more informed field application. Furthermore, the study offers a framework for optimizing EOR strategies tailored to specific lithological and petrophysical characteristics of mature fields, promoting enhanced recovery with economically and environmentally sustainable practices. The main conclusion emphasizes the importance of core-specific evaluation in EOR planning, advocating for tailored recovery strategies based on detailed core analysis and long-term testing. Recommendations include adopting a combination of polymer and surfactant flooding in sandstone-dominated reservoirs and considering thermal methods where geological conditions support thermal energy retention. It also suggests further research into nanotechnology-enhanced EOR agents and the development of real-time monitoring techniques to optimize injection parameters dynamically, ultimately extending the productive lifespan of mature oil fields.