Diagenetic and Reservoir Quality Variation of Miocene Sandstone Reservoir Analogues from Three Basins of Southern California, USA

Sunday E. Okunuwadje*, David MacDonald, Stephen Bowden

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)


The Miocene sandstone deposits in the Southern California region are important hydrocarbon reservoirs. However, their development has been very challenging due to the wide variability in their reservoir quality. These sandstones have been studied from three sedimentary basins by petrographic thin section, scanning electron microscope, and X-ray diffraction to evaluate and compare the influence of diagenesis on their reservoir quality in these basins. Four petrofacies, namely P1 (sand injectite or dyke), P2 (sub-marine fan), P3 (turbidite and marine-influenced alluvial fans) and P4 (continental sandstones) have been identified. P1 and P2 characterise the sandstones in the San Joaquin forearc basin and are affected by kaolinite and extensive early calcite diagenesis. P3 and P4 delineate the sandstones in the Cajon Valley and Salton Trough strike-slip basins and are dominated by smectite, mixed illite-smectite, early calcite and late calcite diagenesis. Early calcite cement in P3 and P4 is in lower proportion than in P1 and P2. Although the dissolution of these sandstones by acidic fluids did not have a pattern, it, however, has the most considerable influence on P2 creating moldic pores which are expected to increase pore connectivity. The relatively abundant dissolution pores in P2, together with the absence of late authigenic calcite and illite clay in comparison to the other petrofacies studied are likely to make this sandstone facies the best reservoir targets in the Southern California region. These rocks are analogous to producing reservoirs in the region. However, because, petroleum accumulation in these reservoirs are compartmentalized by early calcite cement, maximum recovery using acidified fluids is recommended to dissolve the calcite-filled pores in order to increase connectivity of their pore network and enhance flow potential.

Original languageEnglish
Pages (from-to)930-949
Number of pages20
JournalJournal of earth science
Issue number5
Publication statusPublished - 26 Oct 2020

Bibliographical note

The author Sunday E. Okunuwadje wishes to thank the University of Aberdeen for an Elphinstone PhD Scholarship, and Niger Delta Development Commission (NDDC) for financial assistance which has enabled him to take up this study as part of his PhD programme. Endeeper provided the Petroledge software used for the petrographic studies. Mr. John Still, School of Geosciences, University of Aberdeen provided technical support. The final publication is available at Springer via https://doi.org/10.1007/s12583-020-1289-7.


  • California
  • diagenesis
  • Miocene
  • petrofacies
  • reservoir quality


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