Project CHI: Fundamentals of CO2-Hydrocarbon Interactions for CO2 storage

What we do

Project CHI has carried out basic research on CO2-hydrocarbon interactions for CO2 storage in oil and gas reservoirs that could fundamentally alter the ability to recover trapped hydrocarbons while simultaneously maximizing CO2 storage. The project has focused on two processes, convective mixing and wettability, which were chosen because recent experiments show compelling results that may have a significant, yet still largely unknown, impact on field-scale fluid flow (recovery) and trapping (storage). Convective mixing of CO2 in oil is caused by density variations in CO2-oil mixtures. It increases the mixing of injected CO2 with the oil, and this also modifies the mobility of the oil (recovery). Wettability is the preference of one fluid to be in contact with the rock surface over another. This impacts the capacity of the rock to trap CO2. However, wettability can change over time.

Why is this important?

Storage of carbon dioxide (CO2) in geological formations is a means to reduce atmospheric emissions of this greenhouse gas. CO2 storage combined with enhanced oil recovery (EOR) or enhanced gas recovery (EGR) is perceived as the most cost-effective method of disposing captured CO2 emissions. It has been performed for many decades in the US and Canada, but traditionally with a focus on hydrocarbon recovery. On the Norwegian Continental Shelf, CO2 storage will be emphasized in order to meet ambitious climate targets set in Norway and Europe.

Goals

Project CHI objectives are:

describe the fundamental properties of convection and wettability in CO2-oil systems;
model the convective and wettability behavior at the fine scale;
capture the interaction of fine-scale processes with large-scale flow dynamics;
quantify the impact of convection and wettability on breakthrough and recovery factors and CO2 storage capacity in realistic EOR or EGR scenarios.

Project outcomes

The project will have an impact for CCS stakeholders. For operators, storage technology has increased TRL from concept to prototyped software for CO2 reservoir simulation. Better understanding of CO2 behavior in saline aquifers, depleted oil and gas fields, and associated with CO2-EOR operations is important for building confidence in the safety and effectiveness of long-term CCS by industry, regulators and society.

A new code has been developed to model convective mixing between CO2 and oil under various conditions. Results show intriguing results for CO2 mixing with oil from below.

A new thermodynamic model for CO2-hydrocarbon mixtures that compares well to the available data.

New models that describe how the petrophysical properties (capillarity and relative permeability) transition from one wettability state to another over time.