Southern Africa hosts over 93% of the continent's energy, which has been conserved in coal seams deposited in various Karoo age sedimentary basins. Carbon dioxide geological storage (CGS) is proving to be an emerging greenhouse gas technology (GHGT), that global governments have elected to mitigate the projected coal use in Southern Africa. One of the major challenges of successfully introducing CGS to the public and world leaders is the significant risk the technology poses to groundwater resources. Lack of public confidence is further coupled by the poor knowledge of the subsurface behaviour of injected media, such as CO2, in South African potential lithological reservoirs. The study has utilised data from a current MSc research, in which the Springbok Flats Coal Basin (SFCB) has been used as the problem set-up. The aim of this study is to determine which FELOW™ mesh geometry would be the most suitable to simulate a CO2 ingress plume within a regional aquifer. The study has utilised principals of dense vegetation zones (DVZ) and density- variable fluid flow (DVFF) when simulating the ingression. The specific objective is to utilise the simulation results to guide amendments of water legislature, towards accommodating CO2 geological injection and storage operations. Results indicate that a combination of high-quality triangular meshes of various geometries, created with the FEFLOW compatible mesh generator, TRIANGLE, produced the best 3D model and simulation results. The basic matrice unit for the DTZ was defined as a quad mesh composed of two right-angled triangles and one equi-angualar triangle (five nodes), while the unit for modelling springs was defined as a quad mesh with four-equi-angular triangles, both used in various scales. The results were used to amend the Stream Flow Reduction Activities (SFRA) policy and thus the aquifer licensing procedure of the National Water Act, in order to accommodate the allocation of aquifer use licenses for CO2 geological storage operations. The amendments illustrate the significance of finite element simulation codes for integrated water resources management policy.
Presenter Name
Tshegofatso
Presenter Surname
Mophatlane
Area
Bela-Bela, Limpopo
Conference year
2013