Field Pilot Injection Strategies for CO2 Foam EOR in a Layered Heterogeneous Carbonate Reservoir

Abstract

Injection of CO2 foam for enhanced oil recovery (EOR) may provide economic incentives for large-scale industrial CO2 storage. An international field pilot research program has been initiated to develop and test CO2 foam systems with mobility control in a heterogeneous carbonate reservoir. Supported by industry and the Norwegian Research Council, a university lead field pilot project applies experimental and numerical efforts to investigate how to improve CO2 sweep efficiency by foam to enhance the oil recovery and store the injected CO2 in the reservoir. This Thesis evaluates foam injection strategies in an inverted 5-spot well pattern to achieve mobility control and increase areal CO2 sweep efficiency. In a simulation effort, using established models on field pilot geology and foam, Surfactant-Alternating-Gas (SAG) injections are compared to pure CO2 injection and Water-Alternating-Gas (WAG) to quantify foam performance. Initially, 11 injection strategies are compared through static performance indicators like cumulative oil production, gas-oil-ratio (GOR), degree of CO2 recycling and the CO2 utilization factor. The most favorable strategies are further analyzed through streamline simulation, CO2 sweep patterns, dynamic gas saturation profiles and quantification of sweep efficiency. SAG is the optimal injection strategy in terms of CO2 utilization factor for oil recovery when compared with WAG and CO2 injection for performance indicators such as reduced GOR, delayed gas breakthrough and reduced CO2 recycling. SAG also produces more oil at equal pore volumes injected due to reduced CO2 mobility and increased sweep efficiency. Three high-permeability layers were identified as thief zones for CO2 flow through simulation and quantification of CO2 sweep patterns. Foam generation in high-permeability layers during SAG injection diverted chase water to surrounding flow zones of lower permeability and increased sweep efficiency.