Successful exploration is built around detailed exploration play fairway analysis and accurate prospect definition. This success is likely to have a higher degree of probability if the geoscientists involved are well-versed in global analogs. However, many E&P teams follow an informal and inefficient process that spans only the knowledge gained from the team's own geological and geophysical experiences.
Subsurface geological analogs should form an integral part of the exploration and workflow process to help reduce
exploration risk. As such, analogs are powerful tools in helping to define exploration plays and in benchmarking exploration prospects. While individual plays and prospects never are exactly identical, key elements can be transferred both within and between basins. Therein lies the power of analogs.
C&C Reservoirs’ field analog product has expanded from its early start as a compendium of field data into a dynamic global analog system, namely the digital analogs knowledge system (DAKS), which captures and analyzes data and information on more than a thousand of the world’s most important reservoirs and fields.
Exploration play fairway analysis
Play fairway mapping defines the geologic elements of the play, which convey to the exploration decision-makers the
key geologic relationships and critical uncertainties of that specific play. By addressing uncertainty and risk as accurately as possible and attempting to reduce it, play fairway analysis enables geoscientists to undertake work-program commitments with a higher degree of confidence.
To achieve this degree of confidence, reliable data is essential. Data can come from three sources: seismic, well logs, and analogs. The role of analogs usually is limited to those of the geoscientist’s prior experience. Exposure to multiple global analogs can give the geoscientist a better understanding of the play being evaluated. By using commercial successful fields as analogs, inherent risks can be managed and possible future volumes predicted with a higher degree of confidence.
Dr. Harry Doust, professor at the University of Amsterdam, has recommended that a structured hierarchical system be
adopted for exploration plays to enable more appropriate analogs to be used and lead to a more meaningful statistical comparison. This hierarchical system should involve the four main elements of an exploration play:
1. Source – The defining element of the play. The DAKS allows for searches to be based on 28 source rock depositional environments;
2. Reservoir – There are 50 searchable depositional system and environmental subunits within the clastic, carbonate, volcanic, and basement reservoir sections of DAKS;
3. Trap – Within DAKS, the trap search can be divided into five major units and 69 subunits and can be further refined by the basin classification (schemes) according to the tectonic regimes; and
4. Seal – The seal element can be searched individually or as a multiple- criteria search to include all or some of the depositional environments, lithology, age, thickness, or seal classification.
The elements are distinct and separate among more than 150 searchable items within the DAKS. For example, using
the structured hierarchical system for a proposed Neogene sourced and reservoired deltaic play, DAKS contains 68 analog reservoir units and 52 individual analog fields for direct comparison with the proposed play. Further analysis of DAKS reveals that the proposed play can be subdivided into (a) six depositional subunits allowing for alternative interpretations, and (b) numerous separate trap types associated with each depositional subunit.
By using a structured hierarchical play definition, the DAKS enables the individual explorer to identify more appropriate analogs. Additionally, the capability to search and crossplot more than 150 technical parameters allows decision-makers to review and better understand the relative risk of their proposed play versus the proven play analogs.
Exploration prospect benchmarking
When a prospect is being proposed to management for drilling, geoscientists need to be confident in the various technical parameters that provide the basis for the drilling proposal. At the time of the prospect proposal, exploration management usually asks two questions:
1. Where is the successful analog?
2. How does this prospect compare to the analog?
DAKS allows for numerous successful analogs to be retrieved to benchmark the prospect. For example, a drillable prospect has been generated and is interpreted to be a Neogene deltaic sand reservoir located within a back-arc setting. By selecting the Neogene and back-arc categories, DAKS indicates that 50 analog fields are present in the system. Further refinement of the search allows only those Neogene back-arc fields with deltaic reservoirs to be listed.
Statistical analysis of the critical technical parameters for these Neogene back-arc deltaic fields can be generated in terms of P10-P50-P90 distributions. Any anomalous value in the technical parameters can be identified readily for further analysis and justification. The proposed prospect can be benchmarked against proven analogs, allowing management to acquire a clear understanding of the range of the parameters for the analogs and how the prospect parameters compare in terms of relative risk.
The addition of a user field/reservoir knowledge system module to the DAKS in the fall of 2010 will allow geoscientists to directly enter the technical parameters of their prospects into the DAKS database. Therefore, they can store data for their prospects in DAKS and directly plot the prospect technical parameters against identical technical parameters for more than 1,000 analog fields contained within DAKS.
Individual field reports, which have been a major part of the C&C Reservoirs database, can be found within DAKS. These analog field reports can be used to further understand each field and, if justified, to refine the prospect parameters.
DAKS enables geoscientists and exploration management to make better decisions via the increased knowledge obtained through inclusion of global analogs in the workflow process.
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