Phase III - Department of Mines and Petroleum

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Triller fault Main Godwit fault U22J faults Plato fault P18J fault Main Barrow Fault Figure 7 Map showing the main faults and the predicted CO 2 plume through time (extent of 1000 year plume indicated by light blue. document G1-TE-Z-0000-PRSX001). Sedimentology Following drilling of the Data Well and evaluation of results, there is now a series of good reservoir and seal data available for incorporation into the geological model at the proposed injection site on Barrow Island. Results from the Data Well have proven to be within the expected range for rock lithology and properties, and the horizons encountered are very close to prognosis, which is extremely encouraging. The well tie to seismic is excellent and also helps reduce uncertainty regarding the gross sedimentological framework in the area of the Gorgon CO 2 disposal project. The scope and quality of work, and the amount of resources committed to the Gorgon CO 2 disposal project (as presented by Chevron during the four engagement sessions), are very impressive. It has been demonstrated that many of the major requirements for CO 2 disposal are satisfied; that is, the upper injection target (Upper Massive Sand) represents a laterally extensive, moderate reservoir quality sandstone with some internal heterogeneity, good for moderating CO 2 migration; it is overlain by poorer quality sandstones (Upper Dupuy), which will also slow CO 2 plume migration. The top seal (Basal Barrow Group Shale) is a laterally extensive sandy mudstone with proven capability to hold back significantly more CO 2 than will be injected, assuming that no migration pathways through the Basal Barrow Group Shale are provided by faults, fractures or wells. A series of sedimentological studies on Data Well cores have been undertaken and could be extremely helpful in reducing uncertainties with regard to characterisation of the Dupuy aquifer. The depositional xxiii
interpretation (Figure 8) as documented in the Data Well sedimentology reports has changed significantly from earlier interpretations and is considered here to be greatly improved. However, there are still some conflicting interpretations made for various units in the Data Well and also for the overall Dupuy depositional setting used by the GJV. As yet the various sedimentological and palynology studies have not been fully integrated and further work is critical in order to improve understanding of the overall depositional setting and sequence stratigraphy (e.g., water depth, sandbody and mudstone geometries). Figure 8 Dupuy depositional model showing an unstable sandy slope setting dominated by gravity driven processes involving sandy turbidites and debris flows (after document ICTPL 3rd Engagement – Reservoir Characterisation and Static Modelling – 5 December 2006.pdf). Sustained injectivity depends on reservoir continuity, and therefore detailed well correlation and sequence stratigraphy studies are a desirable requirement before developing a static reservoir model. The basis for well correlation presented by the GJV appears sound, with all major surfaces defined by interpretation of seismic reflection lines (7 horizons) and palynology to aid chronostratigraphy where possible. The GJV have proved lateral continuity of the seven seismically defined horizons, with possible limited lateral extent for the ps3 surface (near top of the Lower Dupuy). Whilst the broad correlation framework is proven, we recommend that in the light of the new data, a more detailed (if possible sequence stratigraphic) well correlation is attempted. This could form part of the recommended review and integration of all the available petrographic, core analysis, sedimentological and paleontological reports, possibly supplemented by a new report on forams to get a better handle on paleo-water depth. This could improve the GJV understanding of the depositional setting and thus the facies geometry. Containment Simulator Comparisons This part of the review addresses whether the use and comparison of multiple reservoir CO 2 flow simulation modelling products is desirable to demonstrate high confidence in the model output. The Due Diligence Team observed that several packages were available which could adequately simulate the flow of CO 2 beneath Barrow Island following injection. Differences in the output of these various modelling packages generally arise due to variations in the fluid properties entered into the models. We are not aware that CHEARS, the in-house simulation model used by Chevron, has been involved in any published benchmarking studies of CO 2 flow simulation. However, although we concluded that CHEARS addresses fluid flow and should adequately predict the pressure, saturation and composition distribution in the Dupuy Formation, it should be benchmarked against other simulators. xxiv
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Phase III - Department of Mines and Petroleum

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