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Introduction
Evaluation of exploration prospects requires capability to high-grade
targets by prediction of hydrocarbon charge. This includes both the
likelihood of charge and the type of products to be found, e.g., gas,
condensate, light oil, or normal oil. This can be accomplished by
detailed evaluation of potential source rocks to see which sources will
be effective, i.e., generate, expel, and charge a trap. This is
accomplished by evaluating the petroleum potential, products likely to
be generated, thermal maturity, rates of kerogen decomposition, and
ultimately to predict the timing of generation and hydrocarbon charge.
By combining geochemical data and maps with basin models optimized with
these geochemical data, prospects can be high graded prior to drilling.
Obviously, detailed assessment of traps, their size, drainage areas, migration pathways, i.e., the geology and geophysical assessments, are central to this evaluation. However, as Shell has shown, forecasting efficiency can be increased 63% when geochemical evaluations are included in prospect assessments (Murris, 1984).
Having access to source rocks and geochemical data from many of the basins around the world would certainly aid this assessment.
One of the key concepts put forth by Williams assessment of Williston Basin (USA) oils was that a lot of information regarding source rocks could be gleaned from oil chemistry (Williams, 1974). Understanding the characteristics of source rocks and the presence of multiple oil families, i.e., multiple sources, further amplifies the ability to target the right prospects. Having access to oils would certainly aid these assessments.
World Source Rock and Oil Libraries
World Source Rock LibraryThese data are assembled into multiple volumes (Volumes 1 and 2 are complete with TOC, Rock-Eval, and bulk kinetics data). A complete listing of all samples is included in the Humble World Source Rock Geochemical Library listing (Caution: This file is large so please be patient during loading).
Source rock data is concisely described and illustrated by data and simple graphical displays. For example, sample descriptions and TOC and Rock-Eval data are provided on a single page (Figure 1).
Figure 1. Source rock summary page
Bulk kinetic data are also summarized in tabular form with discrete, Gaussian, and nucleation model results reported. The relative rates of decomposition are summarized by a plot of calculated generation and transformation rates at 3.3° C/my. This arbitrary model allows direct comparison of the rates of decomposition of kerogen and their extent of conversion relative to each other at a given temperature or vitrinite reflectance (%Ro) value (Figure 2).
Biomarker data is available on many samples allowing correlation to seeps or discovered oil pools (Figure 3).
Even light hydrocarbon fingerprints are available on many source rocks enabling correlation to condensates (Figure 4) or produced oils to evaluate whether oils are fractionated or derived from different sources.
Figure 2. Summary of bulk kinetics data showing transformation and generation rate curves calculated at 3.3° C/my with the distribution of activation energies and single Arrhenius factor plus rock information and data.
Figure 3a. Hopane (191 m/z) ion chromatogram, used in correlation of rocks to oils or seeps.
Figure 3b. Triaromatic (231 m/z) ion chromatogram, used in correlation of rocks to oils or seeps.
Figure 4. Light hydrocarbons thermally extracted from rock samples (Bakken Formation) using thermal extraction high resolution chromatography. This enables correclatation of light hydrocarbons from rock samples to light hydrocarbons found in oil and condensates.
World Oil Library
Oil samples are an invaluable asset when trying to evaluate petroleum
systems present in a basin. By typing and correlating oils the
effective source rocks in a basin, or characteristics of likely source
rocks can be evaluated by basic geochemical techniques. These
techniques include high resolution light hydrocarbon and whole oil gas
chromatography, biomarker assessment, carbon isotopic evaluation, and
other chemical and physical properties data such as sulfur, API
gravity, percent wax, pour points and the like.
High resolution light hydrocarbon data can be used to evaluate different oil types in normal oils, but also in condensates (ten Haven, 1995; , 1995). For example, a comparison of Madison Group oils to Bakken Formation oils in the Williston Basin, USA clearly shows that the Madison oils are not derived from Bakken Formation source rocks ( et al., 1995) (Figure 5). Furthermore, correlation between light hydrocarbons from Bakken and Mission Canyon formation source rocks, shows that the Madison oils are likely derived from Mission Canyon or other carbonate source rocks in the basin, not the Bakken shales ( and Walker, 1997).
Biomarker analysis can also be used to correlate and type oils, which has been very well documented over the years. These data can also be used to assess source rock lithofacies (without seeing the source rock itself!) (Hughes et al, 1995) (Figure 6). For example, Figure 6 suggests that a unidentified carbonate rock is the source of Madison Group oils.
Figure 5. Light hydrocarbon data illustrating separate grouping of Madison Group oils from Bakken Formation oils. Also source rock light hydrocarbon data shows high correlation of Mission Canyon source rock sample to Madison oils and Bakken source rocks collate to Bakken oils and the Lodgepole carbonate mound oil.
Figure 6. Lithofacies interpretation scheme from oil geochemistry based on Hughes et al. (1995)
The World Oil Library provides a collection of oils that can be drawn upon to make these correlations and to evaluate likely sources. The oils presently in inventory are listed in the Humble World Oil Library Listing (Caution: This file is large so please be patient during loading).
When rates of kerogen decomposition need to be assessed without the availability of an immature source rock, oil fraction kinetics can be utilized ( et al., 1999). Thus, rates of source rock decomposition in basin models can be optimized from analysis of oil samples.
Access to these Libraries
Access to these libraries is open to any company. However, contribution
of samples is required. These contributions may be source rock samples,
complete well samples (for profiling a well), reservoir core samples,
or oil samples either from production or tests (e.g., DST oils).
Data is charged as withdrawn from the Libraries or the complete set of data may be purchased en masse. Please contact for more information.
References
, , , and , 1999,
Petroleum Asphaltenes Reflect Source Rock Stability at Time of Liquid
Phase Generation, Nature, submitted.
, 1995, Development and Applications of Light-Hydrocarbon-Based Star Diagrams, AAPG Bull., Vol. 79, No. 6, pp. 801-815.
Hughes, W.B., Albert G. Holba, and Leon I. Dzou, 1995, The ratios of dibenzothiophene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks, Geochimica et Cosmochimica Acta., Vol. 59, No. 17, pp. 3581-3598.
, P. R. Walker, and L. C. Price, 1997, Geochemical Comparison of Paleozoic Oils, Williston Basin, U.S.A., 1997 Rocky Mountain Section Meeting Amer. Assoc. Pet. Geologists, August 24-27, 1997, Denver, CO, oral presentation.
, and P. R. Walker, 1997, Correlation of oils and source rocks in the Williston Basin using classical correlation tools and thermal extraction high resolution C7 gas chromatography, 18th International Meeting on Organic Geochemistry, September 22-26, 1997, Maastricht, The Netherlands, oral presentation.
Murris, R. J., 1984, Introduction, Petroleum Geochemistry and Basin Evaluation, AAPG Memoir 35, G. Demaison and R. Murris, eds., pp. x-xii.
ten Haven, H. L., 1996, Applications and limitations of Mango's light hydrocarbon parameters in petroleum correlation studies, Org. Geochem., Vol. 24, No. 10/11, pp. 957-976.
Williams, J.A., 1974, Characterization of Oil Types in Williston Basin, The American Association of Petroleum Geologists Bulletin, Vol. 58, No. 7, pp. 1243-1252.
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