The Agadem Rift Basin (“ARB”) in South East Niger, which forms part of the larger Central African rift system, has proven to be one of the world’s most successful exploration provinces since 2008, with an estimated 1 billion bbl 2P reserve base established and an exploration success rate of 81%. Savannah entered into two onshore Production Sharing Contracts (“PSCs”) in Niger in 2014 and 2015 – R1/R2 and R3/R4. During H1 2022, the four licence areas in Niger were amalgamated into a single PSC (R1234) valid for up to a further 10 years. This has laid the foundation to progress plans for the R3 East Early Production Scheme.
Savannah’s acreage covers approximately 50% of the ARB, an area equivalent to the Central North Sea Basin. The ARB is a well understood and technically low-risk petroleum basin which offers a low-cost operating environment and benefits from large-scale “open access” planned third-party infrastructure and a well-established oil service industry. Since entering into our two PSCs in 2014 and 2015, we have successfully conducted a series of extensive work programmes. This has included the acquisition and interpretation of new airborne geophysical (2014/15) and 3D seismic (2016/17) surveys, the construction of an extensive proprietary basin-wide subsurface model (2014 to date), the discovery of five oil fields (2018) and the submission of our initial field development plan to the Nigerien authorities (2019).
The ARB evolved in two main rift phases (early Cretaceous and Tertiary), resulting in sediments of up to 10km being deposited in the basin centre. To date, most of Savannah’s discoveries have been made in the Sokor Alternances, with the average size of discoveries of c. 30 MMstb oil in place. This can be explained by the high probability of all petroleum system elements (i.e. source rock & migration, reservoir presence, trap & seal) being present within this Tertiary play. Savannah’s additional five prospects and leads within tie-in distance to the planned R3 East facilities are located within the R3 licence area, with three Yogou Cretaceous prospects mapped on 3D seismic, at depths below our main discoveries (i.e. Amdigh, Eridal, Bushiya and Kunama), and two leads in the Central part of R3. Savannah has identified 146 potential exploration targets in total to consider drilling in the future. CGG has stated that estimated average play geological chance of success for the Alternances exploration prospects and leads, such as those drilled to date by Savannah in the R3 East area, is high, at more than 75%.
A world-class exploration province
The favourable structural setting of the traps, combined with seemingly excellent migration efficiency and charge timing from the Lower Yogou marine shale, helps to explain the exceptionally high rate of discoveries, with almost all defined traps containing producible hydrocarbon fluids. Good quality reservoirs are also present at many levels within the Alternances and on a regional basis, reservoir presence and quality are seen as being low-risk play elements. Many analogue structures to known discoveries have been identified on seismic data (limiting trap risk) and remain to be drilled. While the sealing effectiveness will depend on fault juxtaposition, the stacked reservoir arrangement of the Alternances will mitigate against any side-seal uncertainty and help to increase the overall exploration success rate of 115 discoveries from 142 exploration wells.
The presence and effectiveness of all the petroleum systems elements demonstrates the low-risk profile of the Sokor Alternances play. Our 2018 exploration campaign (five out of five well exploration success) is testimony to this. In addition, several light oil discoveries have been made in the Cretaceous Yogou play directly to the South East of Savannah’s R3 Licence area, which highlight the potential upside from this under-explored play.
Understanding the high success rate
Source rock & migration risk
The primary source rocks in the ARB are Lower Yogou marine shales. Oil shows and discoveries have been proven across the length and breadth of the basin, proving the effectiveness of the migration system. The green areas on the map demonstrate the extensive modelled expulsion of oil; the volume of oil generated materially reduces source and migration risk.
Reservoir presence risk
All wells drilled on the ARB have found reservoir within the Sokor Alternances, the primary play in the basin. The map shows the proven net reservoir within wells which penetrated this horizon.
Trap & seal risk
The ARB has a simple structural configuration, with only one predominant fault trend. There are five to six stacked reservoirs in the primary Sokor Alternances play; this, combined with well defined traps on 2D and 3D seismic, serves to limit trap risk on an individual prospect.