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TitleA revised method for organic porosity estimation in shale reservoirs using Rock-Eval data: example from Duvernay Formation in the Western Canada Sedimentary Basin
AuthorChen, Z; Jiang, C
SourceAmerican Association of Petroleum Geologists Bulletin vol. 100, no. 3, 2016 p. 405-422, https://doi.org/10.1306/08261514173
Year2016
Alt SeriesEarth Sciences Sector, Contribution Series 20140280
PublisherAssociation of American Petroleum Geologists
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
ProvinceAlberta
NTS83
AreaWestern Canada Sedimentary Basin
Lat/Long WENS-119.0000 -111.0000 56.0000 52.0000
Subjectsfossil fuels; geochemistry; petroleum resources; hydrocarbons; source rocks; reservoir rocks; porosity; organic carbon; thermal maturation; lithology; sedimentary rocks; shales; models; Upper Devonian; Western Canada Sedimentary Basin; Duvernay Formation; organic porosity; total organic carbon (TOC); hydrocarbon expulsion efficiency; Phanerozoic; Paleozoic; Devonian
Illustrationstables; geological sketch maps; profiles; graphs; diagrams; plots; schematic diagrams; cross-plots; photomicrographs
ProgramShale-hosted petroleum ressource assesment, Geoscience for New Energy Supply (GNES)
ProgramecoENERGY Innovation Initiative
AbstractStudies suggest that nanometer-scale pores exist in organic matter as a result of thermal decomposition of kerogen. Depending on the host rock lithology, organic pores could be the primary storage for hydrocarbon accumulation in unconventional petroleum plays. Although various methods are publicly available, estimation of organic porosity remains a challenge because the procedures involve certain simplification or some implicit assumptions on the calculation of initial total organic carbon (TOC). In this study, we propose a revised method to address some of these issues. A model of estimating hydrocarbon expulsion efficiency is developed and incorporated into the calculation of initial TOC, thus producing an estimate of organic porosity with an improved mass balance. The method has been tested and compared with estimates using other methods based on a Rock-Eval data set in the literature. An application of the method to a large data set from the Upper Devonian Duvernay Formation petroleum system in the Western Canada Sedimentary Basin reveals that the modification has a significant effect on the estimated organic porosity. This study also indicates that organic porosity in the Duvernay Formation ranges greatly from none in immature intervals to >6% in highly mature and organic-rich shale intervals. Scanning electron microscope images of immature and mature organic-rich shale samples of the Duvernay Formation show a progressive increase in organic porosity with increasing thermal maturity, supporting the proposed model calculation. The presence of a large volume of organic porosity in mature shale intervals suggests a significant amount of hydrocarbon may be stored in the organic nanopores in the Duvernay Formation.
Summary(Plain Language Summary, not published)
Advances in drilling and completion technologies have changed the supply-demand dynamics in global petroleum markets. A fundamental shift is happening in North American energy markets with fast development of shale gas and tight oil. Evidence suggested that nano scale pore exists in organic matters and could be the primary storage for hydrocarbon accumulation in unconventional reservoirs. Although various methods are available, estimation of organic porosity remains a challenge. A new method has been developed to address the challenges. The method has been tested and compared with estimates by other methods based on samples in the literature and a large dataset from the Upper Devonian Duvernay Shale in Western Canada Sedimentary Basin. The results reveals that organic porosity estimates may vary considerably with different assumptions and that organic porosity in the Duvernay shale varies greatly from none in immature intervals to >6% in high maturity shale intervals.
GEOSCAN ID295488