Basin data holds the key to developing new value in geological provinces by challenging or supporting assumptions, qualifying potential, and reducing risk.

There are more than 1,500 sedimentary basins of various sizes in IHS Energy's Basin Database (excluding North America), yet nearly half of these remain unexplored for hydrocarbons and have experienced no drilling activity. Of those drilled, only around half have registered discoveries, and only 21% of the drilled basins have more than 100 MMboe of recoverable reserves.

Rather than depicting a pessimistic view for new venture opportunities, the high number of unexplored basins actually offers huge potential. However, this assumes that the probability of finding hydrocarbons can be proven and that the risk can be properly assessed.

Basin data analysis presents a route to achieving this, but it is not without its complications. The analysis of basin data involves many disciplines and a thorough understanding of geological processes. Opportunities for hydrocarbon discoveries within upcoming basin blocks seem to represent often under-exploited prospects for explorationists, yet the risks are high. Even if the opportunities are supported by the right seismic data, it would be reassuring for an explorationist to see exploration and production figures for other areas with a similar geologic profile or to examine the geologic history in more detail as compared to other basins with a proven exploration record.

The concept of locating good geological knowledge of a specific area, comparing that data against the basin-forming processes of lesser-known basins and identifying new exploration opportunities sounds simple enough. Yet such comparisons require a common definition of geological parameters, from age definition to basin classification. To date, a lack of existing standards for these parameters has made it difficult to query data on any of the geological processes between basins at a worldwide or regional scale.

While there have been several standards proposed, the overall lack of a common standard for visualizing and comparing basin attributes and sedimentary environments has not only presented problems in evaluation of existing data but also proven problematic in the entry and handling of new data as it becomes available.

To solve these industry-wide problems, IHS Energy began development of a consistent, global basin database using common parameters and then, working in collaboration with Eni-Agip, developed a basin-data analysis application called BASE. Collectively, this forms a common, standardized method for visualizing and comparing basin attributes and sedimentary environments on a worldwide basis. This standardized methodology then allows accurate queries and comparisons to be conducted.

Within this application, the Basin Evolution Diagram (BED) resembles the Basin Classification Summary Form of Kingston et al. (1983), and also shares some similarities to the Petroleum System Chart. The BED displays the age-interval for different geological processes or items on a horizontal age-scale. By visualizing the basin evolution and associated attributes of the sedimentary fill in a coherent way, the BED enables a geologic interpreter to quickly identify which processes took place during a certain geological period.

Parts of the lithostratigraphic units such as source rocks, reservoirs or seals are assigned hydrocarbon significance. Specific attributes are stored in the basin dataset for each item. For example, geochemical data is stored for source rocks and porosity, and permeability data is stored for reservoirs. Individuals using the application can also modify the attribute data.

Because data is stored in a consistent way within the Basin Database, simple event-queries are possible on a worldwide scale. For instance, an event query can be conducted to find basins containing carbonate reservoirs with certain porosity and permeability ranges. The tool also allows a geoscientist to build complex, evolutionary queries. An evolution query interrogates changes in basin-forming processes, for example, the evolution of one basin type into another one. Such a query could select basins that were originally located on an intracratonic plate but later became an active-divergent continental margin. To test the occurrence of certain processes on a regional or worldwide scale, several combinations of evolution and event queries are possible.

Challenging prevailing assumptions

Recently, basin data has played a major role in challenging prevailing assumption on petroleum geology in certain key regions - pointing to exciting speculative new systems and play concepts.
The hydrocarbons reported in the Trondelag Platform area offshore mid-Norway have long been thought to have been sourced from the adjacent Donna and Halten Terraces. However, because of the presence of the Nordland Ridge, which acts as a barrier to hydrocarbon migrating from the adjacent terraces (Bugge et al., 2002), oil shows found in Lower Jurassic sandstones in several wells drilled in the northern part of the Trondelag Platform (e.g. Helgeland Basin) cannot be related to these known source rocks (Figure 1). Jurassic sandstone reservoirs are well established plays in the Donna and Halten Terraces but were thought to have little potential in the northern part of the Trondelag Platform. However, the presence of the above-mentioned oil shows suggest that a separate petroleum system is actually active in the area.

By comparing the petroleum systems of the Trondelag Platform and the petroleum system described in the East Greenland region and as defined in the IHS Energy Basin Database, Phillips et al. (2003) confirmed that these hydrocarbon shows could have a different origin. In fact, Upper Permian-Lower Triassic fully marine clastics and reworked sabkha sediments have been described on the Trondelag Platform by Bugge et al. They are comparable to rocks of the same age exposed onshore East Greenland Basin. The authors concluded that the marine depositional basin which existed at this time between Greenland and Norway might have thus extended much farther east than previously thought and that the Upper Permian-Lower Triassic source rocks identified in the East Greenland Basin could underlie the Norwegian shelf as well. Sandstone reservoirs and possible seals and traps, which are analogous to those found elsewhere either in East Greenland or offshore mid-Norway, are thus present in the northern part of the Trondelag Platform. These elements, coupled with the possible existence of a mature Permo-Triassic source rock, make the northern part of the Trondelag Platform potentially interesting for future exploration.

A systematic approach to all basins

Placing the petroleum systems and plays in their basin-history context allows a systematic approach to all basins, drawing upon independent data to draw valid and accurate conclusions. Therefore, a geologist with only regional expertise can apply knowledge to any basin worldwide and run viable applications. This provides a valuable tool in appraising prospect opportunities.

Using the IHS Energy data, Coward et al. (1999) analyzed the distribution of petroleum reserves in basins of the South Atlantic Ocean. The study took a systematic approach to the principal basins along both margins of the South Atlantic Ocean, looking at the distribution of the reserves in terms of large-scale tectono-stratigraphic units that are described in the basin database.

As a result, the basins located on the margins of the South Atlantic Ocean have been grouped geographically into seven sectors within which both margins share common features (Figure 2 and Table 1). It is important to notice that 65% of hydrocarbon reserves identified in these seven sectors are contained on Sector V, which is dominated by the Niger Delta, and 28% are positioned in Sector III, which includes the Campos and Lower Congo basins. The recently discovered deepwater giant fields of Angola, which are located in Sector III, are the Africa counterparts of the earlier deepwater Campos Basin discoveries.

In general, Sectors III-V are most favorable for exploration in the South Atlantic region. The most productive part is expected to be Sectors III and IV, characterized collectively by the occurrence of pre- and post-salt source rocks, salt-related structures, tectonic tilting and related Tertiary loading.
With this in mind, Sector IV in Gabon appears particularly interesting in the deepwater area, west of the mouth of the Ogooue River. Exploration in the deepwater Niger Delta (e.g. Sector V) is expected to continue to add reserves which, once produced, would add to an already enormous reserve base.

Improving system understanding

By covering the world's most significant hydrocarbon provinces, global basin data is helping improve the total understanding of petroleum systems.

A study on Oligocene to Pliocene basins with a deep-marine depositional setting was recently conducted using data from the Basin Database. The aim of the study in particular was to investigate the reserves potential of deepwater sandstones in structural and stratigraphic traps. Using the query builder, a total of 25 basins worldwide were selected after matching the initial criteria of deep-marine settings (Figure 3).
The geological evolution of the selected basins was then compared. Although the majority of deepwater reserves are located in stratigraphic traps, (37% of all deepwater reserves) and combined stratigraphic-structural traps (46%), important differences exist between basins as demonstrated by the Basin Evolution Diagrams.

Only seven basins of the 25 identified hold significant reserves. Integrated data within the basin and field databases allowed an evaluation of reserves found to date with the potential for discovering future reserves. The Campos Basin offshore Brazil, the Niger Delta and Congo Fan in West Africa, and the Kutei Basin in Indonesia are the most prospective regions for future deepwater exploration, although significant differences in potential discovery sizes exist between the basins, ranging from more than 500 MMboe in the Campos Basin and Niger Delta to less than 200 MMboe in the Kutei Basin. Additional potential might exist in under-explored areas like the deepwater part of the Baram Delta, but at a higher exploration risk.
To complete the study, researchers mapped the extent of source rocks and reservoirs in the interactive Play Map, which required play fairways to be drawn for undiscovered hydrocarbon accumulations in Oligocene-Pliocene deepwater settings (Figure 4). The results of this study will be presented at a geological conference later this year.

Achieving a return on these findings

In addition to presenting a fascinating viewpoint of basin history and hydrocarbon prospectivity, the availability of consistent global basin data is proving to be a valuable business tool for explorationists and new venture teams. It allows explorationists with limited time and perhaps only regional experience to gain a valid understanding and evaluation of other regions worldwide. And perhaps more importantly, applications now available in the database are enabling explorationists to use basin data to present stronger business models, elevating geology in the business-decision process and providing a vital role in improving return on investments.

More information about BASE can be found in "BASE, a new tool for basin analysis and visualization of geological processes." (Roelofsen, J., Cadel, G., Arbouille, D. & Alverti, E., 2002. Abstracts EAGE 64th Conference & Exhibition, Z-99.)

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