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Impact of diagenesis on reservoir-quality evolution in fluvial and lacustrine-deltaic sandstones: evidence from Jurassic and Triassic sandstones from the Ordos Basin, China
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
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2009 (English)In: Journal of Petroleum Geology, ISSN 0141-6421, E-ISSN 1747-5457, Vol. 32, no 1, 79-102 p.Article in journal (Refereed) Published
Abstract [en]

The reservoir quality of Jurassic and Triassic fluvial and   lacustrine-deltaic sandstones in the intracratonic Ordos Basin is strongly influenced by depositional facies and various types of   diagenetic modifications. The fluvial sandstones have higher average He-porosity and permeability (14.8% and 12.7 mD, respectively) than the deltaic sandstones (9.8% and 5.8 mD, respectively). In addition to extensive mechanical compaction, eodiagenesis (220-97 Ma; depth < 2000 m; T < 70 degrees C) has resulted in dissolution and kaolinitization of detrital silicates in the Jurassic fluvial sandstones, and in smectite infiltration and minor cementation by calcite and siderite in the Triassic fluvial and deltaic sandstones. Pervasive eogenetic carbonate cementation (> 20 vol.%) occurred in Triassic deltaic siltstones and very fine-grained sandstones which are closely associated with organic-rich mudstones. Mesodiagenesis (97-65 Ma), which occurred during rapid subsidence to depths of 3700-4400 m, resulted in the albitization of plagioclase, checmical compaction, the conversion of   kaolinite into dickite, and cementation by quartz overgrowths, chlorite, illite, ankerite (delta C-13(VPDB) = -2.4 parts per thousand to +2.6 parts per thousand; delta O-18(VPDB) = -21.5 parts per thousand to -10 parts per thousand) and calcite (delta C-13(VPDB) = -4.7 parts   per thousand to +3.7 parts per thousand; delta O-18(VPDB) = -21.8 parts per thousand to -13.4 parts per thousand). Oil emplacement (95 Ma) retarded cementation by mesogenetic quartz and carbonate but had little influence on dickite, illite and chlorite formation. Retardation of quartz cementation was also due to the presence of chlorite fringes around detrital quartz grains. Dickitization of eogenetic kaolinite together with the short residence time at maximum burial temperatures (105-124 degrees C) has retarded the albitization of K-feldspars and illite formation and hence prevented severe permeability destruction.   Telodiagenesis, which occurred after uplift (Eocene to end-Neogene), caused slight dissolution and kaolinitization of feldspars. This study demonstrates that despite complex patterns of diagenetic modifications in the Triassic and Jurassic successions, depositional   porosity and permeability are better preserved in fluvial meandering channel sandstones than in deltaic sandstones. These results should be important for modelling of reservoir-quality distribution and exploration risk evaluation in the basin.

Place, publisher, year, edition, pages
2009. Vol. 32, no 1, 79-102 p.
Keyword [en]
Diagenesis, reservoir quality, fluvial and lacustrine-deltaic sandstones, Jurassic, Triassic, Ordos Basin, China
National Category
Earth and Related Environmental Sciences
Research subject
Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
URN: urn:nbn:se:uu:diva-119810DOI: 10.1111/j.1747-5457.2009.00436.xISI: 000261881800005OAI: oai:DiVA.org:uu-119810DiVA: diva2:301013
Available from: 2010-03-02 Created: 2010-03-02 Last updated: 2013-09-13Bibliographically approved
In thesis
1. Diagenesis and Reservoir-Quality Evolution of Paralic, Shallow Marine and Fluvio-lacustrine Deposits: Links to Depositional Facies and Sequence Stratigraphy
Open this publication in new window or tab >>Diagenesis and Reservoir-Quality Evolution of Paralic, Shallow Marine and Fluvio-lacustrine Deposits: Links to Depositional Facies and Sequence Stratigraphy
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Linking diagenesis to depositional facies and sequence stratigraphy enables better prediction of spatial and temporal distribution of diagenetic alterations, and thus of evolution of reservoir quality in sandstones. This thesis demonstrates that employing this approach is possible because depositional facies and sequence stratigraphy can provide useful information on parameters controlling the near-surface diagenesis, such as changes in: (i) pore-water chemistry, (ii) residence time of sediments under certain geochemical conditions, (iii) detrital composition and proportion of extra- and intra-basinal grains, and (iv) types and amounts of organic matter.

Evidence from four case studies enabled the development of conceptual models for distribution of diagenetic alterations and of their impact on evolution of reservoir quality in sandstones deposited in paralic, shallow marine and fluvio-lacustrine environments. Diagenetic alterations that have been constrained within the context of depositional facies and sequence stratigraphy include: (i) carbonate cement (microcrystalline and equant calcite spars dolomite over poikilotopic calcite), pyrite and glaucony are most abundant in progradational braid-delta fan sequences, particularly along the topsets (i.e. maxiumum flooding surface, MFS) and along parasequences boundaries in the deltaic facies of the early highstand systems tract HST, (ii) cementation by coarse spar calcite, dolomite, and the formation of moldic porosity by the dissolution of framework carbonate grains are most abundant in the aggradational fan deltas sequences, (iii) eogenetic kaolinitization of framework silicates is largely restricted to the fluvial and paralic HST sandstones, whereas telogenetic kaolinite may occur in the transgressive systems tract TST sandstones too, (iv) formation of goethite ooids in the TST sediments, (v) formation of glaucony, siderite spherules, and extensive grain-coatings, grain-replacing and ooidal berthierine, more in the TST than in the HST sediments, particularly below the transgressive surface TS and MFS, (vi) cementation by calcite with (δ18OV-PDB = -11.5‰ to -5.4‰) and Fe-dolomite/ankerite (δ18OV-PDB = -10.8‰ to -9.6‰) occurs in both TST and HST sandstones, (vii) syntaxial quartz overgrowths are most extensive in the HST sandstones owing to the presence of incomplete grain-coating berthierine/chlorite, (viii) greater amounts of micro-porosity in the TST sandstones than in the HST sandstones are related to the greater amounts of berthierine/chlorite in the former sandstones, and (ix) chlorite rims around quartz grains retarded the precipitation of quartz overgrowths, and hence prevented a greater loss of primary intergranular porosity in fluvio-lacustrine sandstones. Therefore, constraining the distribution of diagenetic alterations in the contexts of depositional facies and sequence stratigraphic context is a powerful approach to be used in hydrocarbon exploration.

Place, publisher, year, edition, pages
Uppsala: Universitetsbiblioteket, 2008. 65 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 448
Sandstone, Diagenesis, paralic, shallow marine and fluvio-lacustrine, reservoir quality, sequence stratigraphy
National Category
urn:nbn:se:uu:diva-8986 (URN)978-91-554-7237-5 (ISBN)
Public defence
2008-05-28, Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Available from: 2008-05-08 Created: 2008-05-08 Last updated: 2013-09-13Bibliographically approved

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