Leakage Simulation Modelling as a Risking Tool in CO2 Geological Sequestration (CocCRC)
Nicolson, Darren S.
Engineering Honours Degree 2007
University of Adelaide
Geosequestration of carbon dioxide (CO2) has a risk of leakage and demonstrating these effects to stakeholders is critical for acceptance. Understanding the leakage scenarios (i.e. failed wellbore, fault or a high permeable zone in the seal) and the effects they have is required for project evaluation.
A homogeneous geological model of the area used by the CO2CRC Otway Basin Project was constructed and used in reservoir simulation software (ECLIPSE) to observe the migration and dissolution of leaked CO2 from a point source. A leakage rate of 10,000tpa was assumed to occur for one year from the Belfast Mudstone to the overlying Paaratte Formation. The results displayed that the leak was contained for a 1000 year period for three cases of vertical permeability; equal vertical and horizontal permeability (kv/kh=1), vertical permeability equal to one-tenth and one one-hundredth of the horizontal permeability (kv/kh=0.1 and kv/kh=0.01 respectively). The vertical migration was greatest for the kv/kh=1 case (least for the kv/kh=0.01 case). This causes the CO2 to contact a greater volume of virgin formation fluid and hence become dissolved, which is evident by comparing the dissolution of CO2 with time for all cases. The CO2 brine phase is the densest phase and due to the larger volume of this phase in the kv/kh=1 case the lateral migration of the CO2 plume is greatest (smallest later migration for the kv/kh=0.01 case).
The effects of a major fault leak (i.e. leakage rate of 30,000tpa for two months) into the Pebble Point Formation were also investigated for the three vertical permeability cases mentioned above. Containment of the leak was displayed for all cases. This is a very important result as it displays the ability of the overlying formation to contain a significant leak of CO2 to a point that is near the top most seal; leakage past this seal is extremely undesirable as it will cause contamination of potable water supplies. Similar migration and dissolution trends to those mentioned previously were observed.
A simplified geological model was used in this study with homogeneous properties; it is recommended that this data be updated as more becomes available to better reflect reality.