Design of Injection Well String for Dissolution Acceleration in CO2 Storage

Mohammad Javad Shafaei

Arising trend in the average earth temperature and its consequences in the climate changes have worried scientists, researchers and governments all around the world. It is believed that anthropogenic greenhouse gases are responsible for the most of the observed temperature increase since the middle of the twentieth century. Carbon dioxide (CO2) emitting from the use of fossil fuels forms the major portion of these gases. One of the most promising proposed mitigations for reducing CO2 emissions is geological CO2 storage in deep saline aquifers. One of the essential concerns in CO2 sequestration is the risk of leakage of CO2 from the injection sites through natural or artificial pathways. Other major concern is the cost of CO2 compression into deep saline aquifers. Injection of CO2 into aquifers demands high compression pressure on the top of the well. In this study, a new design for CO2 injection is presented to first accelerate the dissolution process in formation brine, and therefore, reduce the possibility of leakage in the future, and second decrease the cost of CO2 compression. In this work, a perforated well string configuration is proposed to inject CO2 and brine into saline aquifer simultaneously. CO2 and brine are mixing along the proposed perforated annulus-tubing configuration. This mixing can accelerate CO2 dissolution during injection process before CO2 reaches aquifer. Such novel engineering technique might be feasible and practical. To model and simulate the proposed configuration, the system is considered as a network of source, sink, and junction nodes. The different nodes of the network are connecting to each other through the tubing, annulus, and valve links. In this study, I first present the development of fluid flow models for the valve, annulus, and tubing links. Since the fluid flow through the tubing links is a two-phase flow accompanying with mass transfer, CO2 concentration and pressure distribution profiles are coupled to each other. Complexities in the tubing link flow decreases applying some simplifying assumptions and three different simplified models for CO2 concentration in brine are presented.

Afterward, an integrated model is used to simulate the system and find process parameters in the system. Finally, the effects of brine salinity, surface temperature, bottom-hole injection pressure, gas lift valve diameter, and the absolute roughness of constructed material on pressure distribution and concentration profiles in the tubing and annulus sections are analyzed for different considered dissolution cases. Furthermore, demanded pump and compressor pressures on the top of the well are calculated. Subsequently, conclusions and possible recommendations to improve obtained results are presented.