RE: Cos calcultions9 May 2021 10:36
“Migration
There needs to be a thermal release of the helium produced in ancient deep crust and in Rukwa this is caused by the crust ripping apart due to a mantle plume (upwelling of abnormally hot rock) underneath East Africa. This is exceedingly rare, which is why it is unusual to find large primary helium deposits globally. This rifting and associated magmatism focuses the flow to the near-surface along major basement faults. Helium and nitrogen-rich water is thought to flow along fault and fracture zones. Numerous thermal springs release bubbles of helium and nitrogen through surface seepages, indicating migration along major fault zones.
Reservoir
There are suitable reservoirs at multiple stratigraphic levels that have the capability to hold helium with good porosity. The sandstone reservoirs have been proven by the two wells drilled in 3 stratigraphic levels: the Lake Bed Formation, Red Sandstone Group and Karoo Super Group. The basin is dominated by sand (i.e. potential reservoirs) with shales (potential seals) more sparsely distributed.
Seal
The two historic (dry) petroleum exploration wells in the Rukwa Basin demonstrate stratigraphy with effective seal capacity. Additionally, bentonitic tuff beds described in the Lake Bed Formation and Red Sandstone Group have the potential for high-quality seals. Seals are present within and at the top of the Karoo section as evidenced by the Ivuna-1 well. Observed seismic amplitude anomalies are conformable to structural highs may be related to gas effect in the rock, in which case effective seal is demonstrated although well data is required to confirm this relationship.
Trap
Migration can be halted by seals or traps. If trapping structures are present on the migration pathway, a gas phase can accumulate. The trap will be filled with helium-rich gas until full and then spill. The excess spilt fraction if not trapped further up in the system will escape at surface seeps.
Helium can be trapped at the top of the Red Sandstone by lacustrine shales at the base of the Lake Beds and anywhere within alternating sand/ shales throughout the Lake Bed sequence. The traps can be identified using seismic data. In the Karoo play, the dominant trapping geometry is rotated extensional fault blocks creating 3-way dip closures with fault seal in the 4th direction. The trapping style within the Lake Bed play is more varied than for the Karoo: there are gentle 3-way closures against faults as tested by the Ivuna-1 well and minor inversion structures, low relief 4-way traps, stacked low-relief 3-way traps against the fault. Stratigraphic trapping may also be present within the rift.
Trek
Sign In
Follow the stocks
