On Fluid and Thermal Dynamics in a Heterogeneous CO2 Plume Geothermal Reservoir

Tianfu Xu,Guanhong Feng,Hailong Tian,Huixing Zhu,Yilong Yuan

doi:10.1155/2017/9692517

Abstract

CO2 is now considered as a novel heat transmission fluid to extract geothermal energy. It can achieve both the energy exploitation and CO2 geological sequestration. The migration pathway and the process of fluid flow within the reservoirs affect significantly a CO2 plume geothermal (CPG) system. In this study, we built three-dimensional wellbore-reservoir coupled models using geological and geothermal conditions of Qingshankou Formation in Songliao Basin, China. The performance of the CPG system is evaluated in terms of the temperature, CO2 plume distribution, flow rate of production fluid, heat extraction rate, and storage of CO2. For obtaining a deeper understanding of CO2-geothermal system under realistic conditions, heterogeneity of reservoir’s hydrological properties (in terms of permeability and porosity) is taken into account. Due to the fortissimo mobility of CO2, as long as a highly permeable zone exists between the two wells, it is more likely to flow through the highly permeable zone to reach the production well, even though the flow path is longer. The preferential flow shortens circulation time and reduces heat-exchange area, probably leading to early thermal breakthrough, which makes the production fluid temperature decrease rapidly. The analyses of flow dynamics of CO2-water fluid and heat may be useful for future design of a CO2-based geothermal development system.

Highlights

The enhanced geothermal system (EGS) is defined as an engineered reservoir that has been created to extract economical amounts of heat from geothermal resources of low permeability and/or porosity [1]
The major benefit of the CO2 plume geothermal (CPG) system over the EGS is that the CPG system does not require hydrofracturing, which helps increase fracture permeability but may induce seismicity
As can be seen in the graph, the fluids production rates of hp1 and hp2 are really low during the simulation time, which could affect the economic feasibility of the CPG system

Summary

Introduction

The enhanced geothermal system (EGS) is defined as an engineered reservoir that has been created to extract economical amounts of heat from geothermal resources of low permeability and/or porosity [1]. As part of an effort to reduce atmospheric emissions of carbon dioxide (CO2), a novel concept of operating the EGS using CO2 instead of water as the working fluid (CO2-EGS) and achieving simultaneous geologic sequestration of CO2 has been proposed and evaluated [2, 3]. A similar concept, the so-called CO2 plume geothermal (CPG) system, has been proposed [4]. The CPG system utilizes existing, naturally porous, high permeability geologic formations (reservoirs) for geothermal energy recovery. The major benefit of the CPG system over the EGS is that the CPG system does not require hydrofracturing, which helps increase fracture permeability but may induce seismicity. The EGS has encountered considerable unfavorable conditions and sociopolitical issues (resistances)

Objectives

Results

Conclusion