CO2 ENHANCED OIL RECOVERY BASED ON RESERVOIR COMPACTION, THERMAL MODELING, AND FORMATION DAMAGES

Abstract

Ilyas Khurshid Department of Energy Systems Engineering College of Engineering Seoul National University

The primary objective of this dissertation is to develop new, simple, and robust methods and practices for enhance oil recovery (EOR) and CO2 storage. For this purpose a step by step structure is developed, which will provide a good understanding of interrelationships between rock compaction and CO2 injection time, CO2 thermal modeling, CO2 related formation damages, and methods to minimize these damages.

The first objective is to develop an analytical model using the concept of pore arrangement at macroscopic level. This model along with the proposed failure-line methodology determines a minimum reservoir pressure. This pressure represents the pressure after which permanent pore collapse will occur and it can be used to determine optimal time ranges for CO2 injection. On the basis of detail analysis, an optimal CO2 injection time ranges are to inject it before touching the failure line. This practice will enhance oil recovery and CO2 storage.

The second objective is to determine CO2 temperature profile in wellbore, factors affecting it, and formation damages caused due to heated CO2. For this purpose a simulator is developed and experimental determined specific heat values of CO2 are used to predict the temperature of CO2. This approach results in accurate CO2 temperature predictions, because the thermodynamic properties of CO2 vary with temperature and pressure. From sensitivity analyses of CO2 injection parameters, it is found that the injection rate, injection time, geothermal gradient, and surface temperature play a key role in controlling CO2 temperature in sequestration activities.

When carbon dioxide enters in a reservoir, it may react with the formation leading to immense formation damages such as asphaltene deposition, rock dissolution, and particle precipitation. The third objective is to develop a simulator to model chemical reactivity, pH shift, asphaltene deposition, and particle dissolution and precipitation. It is found that these processes may lead to cementation and result in irreversible damages to the porous media. It is observed that this cementation depends on the amount and reactivity of asphaltene, and the reactivity of CO2 with water and rock. It is also analyzed that substantial amount of cementations occurs for high injection rate and long injection period. From the sensitivity analysis, it is established that deep oil and gas reservoirs are better candidates for CO2 sequestration than shallow reservoirs due to low formation damages.

The final objective of this study is to develop an integrated methodology to minimize asphaltene deposition, and to increase oil recovery and CO2 storage. When CO2 is injected at immiscible conditions, asphaltene deposition is low with less recovery. However, when the conditions are miscible, recovery increases but it also triggers asphaltene deposition. From detail simulation study, it is found that there are a number of minimum miscibility pressures (MMP), but three are important: near, at, and above MMP. For the first MMP there is high asphaltene deposition. When the pressure is at and above the MMP, the deposited asphaltene is removed from the reservoir, because CO2 develops contact with asphaltene at high pressure leading to its redissolution and removal.

Key words: Reservoir compaction, Carbon dioxide injection, Optimal injection time ranges, Thermal modeling, and Formation damage.

Student ID: 2011-31311