Philosophiae Doctor - PhD / Geomechanical analysis and integrity assessment of hydrocarbon reservoirs upon depletion
and injection are crucial to ensure that CO2 storage projects can be safely implemented. The
Bredasdorp Basin in South Africa has great potential for CO2 storage, given its hugely available
exploration data. However, there has not been any geomechanical characterization carried
out on this basin to determine its integrity issues. This study aims to investigate the feasibility
of a carbon storage project in the E-M depleted gas field. The preliminary geological
assessment demonstrates that Zone 2 and Zone 3 display acceptable injectivity for CO2
injection of the E-M gas field. Seismic lines display faults that could affect the caprock's
integrity during depletion and carbon storage. Geomechanical characterization provides a
guideline as to how geomechanical analysis of depleted fields can be done for a safe CO2
sequestration practice. The geomechanical model constructed at a depth of 2570 m indicated
that the magnitudes of the principal vertical, minimum, and maximum horizontal stresses in
the field are respectively 57 MPa, 41 MPa, and 42-46 MPa. Fault and fracture stabilities were
examined before and after depletion. It was found that faults and fractures in compartments
C1 and C2 of the reservoir are stable before and after depletion, while normal faults (FNS8
and FNS9) in compartment C3 dipping SW were critically stressed. The minimum sustainable
pressure of the reservoir determined by simulating depletion is 6 MPa. Below that, pressure
depletion causes normal faulting in reservoir compartments C1 and C2. The maximum
sustainable pressure, on the other hand, was found to be 25 MPa. The geomechanical studies
also reveal that it is possible that the reservoir experienced compaction of 8 cm during
depletion and will experience an uplift of 3.2 cm during 71 years of injection. The economic
model of a CO2-enhanced gas recovery project in E-M gas field, the annual expenses (Aexp) of
carbon capture and storage range between Zar20 3.31 × 109 and Zar20 4.10 × 109. The
annual revenues (RA) were estimated to be Zar20 1.42 × 1010. The cash flow analysis derived
from Aexp and RA confirms that enhanced gas recovery could partially offset the cost of CO2
storage if a minimum of 5 % of CO2 fraction is allowed in the natural gas recovered. Geological
and geomechanical studies have demonstrated that carbon storage is physically feasible in
the E-M gas field. However, the project's completion lies in the among the gas recovered to
balance the cost of CO2.
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| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uwc/oai:etd.uwc.ac.za:11394/8218 |
| Date | January 2020 |
| Creators | Saffou, Eric |
| Contributors | van Bever Donker, J M |
| Publisher | University of the Western Cape |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Rights | University of the Western Cape |
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