Are half of the Tano Basin’s reservoirs in the Keta Basin?

Ghana’s ascendancy as a significant oil and gas pro­ducer commenced with the landmark Jubilee dis­covery in 2007, leading to first oil in 2010. This success was subsequently re­inforced by the discovery of Tweneboa, Enyenra, and Ntomme (TEN) fields.

While historical exploration efforts have predominantly concentrated on the Tano Basin in both Ghana and Côte d’Ivoire – highlighted by recent success at Baleine in the Deep Tano Basin – a compelling new focus is now shifting eastward to the offshore Keta Basin. This basin presents a geological setting ripe for renewed hydrocarbon exploration.

Despite its inherent potential, the Keta Basin has, to date, remained some­what overshadowed. Previous deepwa­ter exploration efforts by ENI, Afren, and Devon Energy have yielded only one sub-commercial gas discovery at Tarpon-1. However, a comprehensive re-evaluation of the Keta Basin’s sed­iment provenance history, integrated with past well results, strongly suggests that the basin shares more geological commonalities with the productive Tano Basin than previously presumed, thereby indicating the potential for analogous hydrocarbon resources.

For International Oil Companies (IOCs), the Keta Basin should represent a very attractive frontier, characterised by its extensive running-room, strategic proximity to existing oil discoveries, and considerable scale, aligning perfectly with modern exploration priorities; all set in an existing oil-producing nation.

Here, we delineate three pivotal reasons underscoring the Keta Basin’s compelling similarities to the Tano Basin, positioning it as a high-poten­tial, yet underexplored, frontier.

1. Provenance and transport path: Keta’s cretaceous sands have the same provenance and transport path as Tano’s

A common challenge in many discover­ies across the Transform Margin has been the sub-commercial nature of reservoirs. While most wells have encountered hy­drocarbon presence, reservoir quality is often compromised due to the mineral­ogical immaturity of the sands.

The Tano Basin stands as a notable exception to this trend, boasting sand­stone reservoirs with excellent perme­abilities that support viable flow rates, enabling fields to progress to develop­ment. Sourced from the Sourou Basin and traversing the Palaeozoic Volta Ba­sin, these systems are much more mature in terms of mineralogical content than many other reservoirs found along the broader Transform Margin.

Crucially, prior to the inversion of the Saltpond High in Early to Mid-Cre­taceous times, both the Black and White Volta fluvial systems were actively feed­ing the offshore Keta Basin (Figure 2a). The subsequent uplift of the Saltpond High during the Campanian redirected the Black Volta fluvial systems westward into the Tano Basin, depositing the pro­lific Mahogany and West Cape Three Points fan bodies. These fans are now host to numerous significant discoveries, including the Jubilee, TEN, and Sanko­fa Fields (Figure 2b; Grant et al, 2018). Consequently, the Keta Basin is endowed with the same mineralogically mature Cretaceous sandstones as the Tano Basin, a critical factor for reservoir quality.

2. Multiple source rocks and post-trap formation expulsion: A Tano analogue

Modelling of source rock expulsion, utilising available well data from the Keta Basin, demonstrates a favour­able timing of trap formation. The syn-rift source rock is modelled to expel hydrocarbons towards the end of the Cretaceous, while the Ceno­manian-Turonian source rock expels in the mid-Eocene in deep water set­tings and the mid-Miocene in shal­lower waters.

Throughout the West African Transform Margin, a significant ex­ploration risk is posed by late-stage tectonism, leading to trap breach. In Côte d’Ivoire, this is a primary cause of deepwater well failures. The success observed in Tano correlates strongly with a period of tectonic quiescence after trap formation. Similar obser­vations are evident in Keta, where inversion ceased in the Campani­an, ensuring that transform-related traps remained intact post-charge. Figure 1 shows a Geoseismic section, with source and reservoir units marked.

3. Exploration history: Keta’s underexplored potential parallels early Yano

The Keta Basin’s deepwater explora­tion history is remarkably limited, with only three 3D seismic surveys and six wells drilled to date. Dol­phin-1, spudded in 2000, followed by NAK-IX and Keta-1 in 2001 (both drilled on 3D data), all yield­ed oil fluid inclusions within Albi­an-Cenomanian shelf-slope deposits. The only deepwater wells in the ba­sin were Tarpon-1 (Devon Energy, 2003), Cuda-1 (Afren, 2008), and Nunya-1 (ENI, 2012), drilled on two 3D surveys. While Cuda-1 and Nun­ya-1 exhibited oil shows, Tarpon-1 encountered a gas-bearing sandstone in the Mid-Miocene. The most recent well, Starfish-1 (Ophir), was dry but notably encountered 230 m of good quality, Tano-style sands in the Low­er Cretaceous.

When compared to the Tano Basin’s exploration history prior to the 2007 Jubilee discovery, the re­sults in Keta are strikingly compara­ble. The first speculative 3D seismic surveys in deepwater Tano were ac­quired from 2000 onwards, prompt­ing Tullow to license the deepwater acreage in 2004. By 2007, the Jubi­lee Field had been discovered in just the second phase of drilling. Similar successes could readily be replicated in the Keta Basin, which has yet to experience a second, more compre­hensive drilling phase.

Future exploration outlook and government support

The combination of these be­low-ground geological factors posi­tions the offshore Keta Basin as an area with significant future exploration potential in Ghana. While seal integ­rity has historically been considered a primary exploration risk in the Keta Basin, new high-resolution 3D seis­mic data and integration with newly defined geological models will actively de-risk this concern. The interpreted development of effective seal litholo­gies and the favourable timing of trap formation, particularly the pre-charge Campanian onlap traps, significantly enhance confidence in seal effective­ness across prospective intervals.

In recognition of this potential, GeoPartners is planning to acquire a 14,000 km² 3D seismic survey in Q4 2025 (Figure 2). This data acquisi­tion is anticipated to be instrumental in de-risking identified prospects, pro­viding advanced subsurface imaging, and attracting further investment re­quired to fully assess the hydrocarbon potential of the Keta Basin.

Additionally, the current govern­ment, facilitated by the Petroleum Commission as regulator, has ex­pressed a clear and positive commit­ment to enhancing Ghana’s oil and gas sector. Initiatives are underway to streamline exploration processes and foster an attractive investment cli­mate, aiming to position Ghana as a key destination for energy investment over the forthcoming years.