As with high gas-oil ratios, reservoir quality is emerging as a significant risk to explorers in the Orange Basin.
- Tamboti’s permeability is ’not good’ and closer to those observed in Shell’s discoveries, including Jonker, where reservoir permeability is about 0.7 mD.
- Pouyanne's exploration team knew about the permeability risk before drilling Tamboti-1X because results from a Venus appraisal well, Mangetti-1X also showed signs of reservoir “degradation.” “Petrophysics are poor" with net reservoir comprising “lower quality Upper Cretaceous sandstones".
- The Venus Oil Field permeability of 2-4mD is certainly not world class.
- At this stage, to lower quality reservoirs are west of the Outer High.
PEL-87
Building on PCL's interpretation that reservoir quality of the Albian turbidite leads of OYRX and HYRAX is "significantly derisked" and therefore likely of better quality than for example Venus, I offer the following thoughts, based on mention of sediment waves noted over OYRX and HYRAX in the last Quarterly.
Sediment waves are generally built upon a more-regional unconformity (e.g. Saturn's sequence boundaries) that separates the underlying strata from the overlying strata containing sediment waves. The generation of bottom current sediment waves is related to bottom current activities which we are invoking in PEL-87. Sediment wave can cover very large areas of many slope and basin-floor settings where the persistent actions of bottom currents are active.
Persistent actions of bottom currents can agitate the sediment through reworking processes which likely winnow out fines such as muds, clays and silts thereby enhancing reservoir quality.
However, there remains risk that muddy sediment may be introduced into otherwise clean sands by bottom current transport during periods of relative turbidite/gravity flow inactivity, with the potential to form extensive (field-wide) horizons of reduced reservoir quality.
Sediment waves dimensions have wavelengths ranging from 0.5 km to 4km (average 2.6 km) and wave heightsbetween 7 m and 117m (average 28m). The deposition of sediment waves is influenced by the along-slope bottom currents and interactions with down-slope (gravity) processes. The diagram below attempts to show the various sedimentary active in PEL-87 during Albian time.
The maps below showing the Ultra-far Seismic Offset AVO response over HYRAX and ORYX with OldGeo's interpretation of what are possibly large-scale sediment waves (black dotted lines) based on trends observed in the amplitude field.
The interpreted sediment waves annotated on the maps above, may be manifest as undulating layers (blue lines) on the seismic section below. There appear to be four (4) stacked complexes.
The map below attempts show a possible analogue field of sediments waves to compare with sediments waves on the Ultra-far Seismic Offset AVO maps above.
Anyway, just sharing some thoughts on potentially reducing reservoir risk through the interaction of bottom current and turbidity/gravity processes, as we await PCL's prospective resource estimates.
OldGeo
(20min delay)