Quartz Diagenesis in Layered Fluids in the South Brae Oilfield, North Sea
Orla M. McLaughlin, R. Stuart Haszeldine, Anthony E. Fallick, 1996. "Quartz Diagenesis in Layered Fluids in the South Brae Oilfield, North Sea", Siliciclastic Diagenesis and Fluid Flow: Concepts and Applications, Laura J. Crossey, Robert Loucks, Matthew W. Totten, Peter A Scholle
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The South Brae reservoir sandstones were cemented by quartz late in their diagenetic history. The volume of quartz cement in the South Brae sandstones ranges from 0 (in early calcite cemented concretions) to approximately 11%, wifh a mean of 3.5%. In four studied wells, quartz overgrowth δ180 decreases with increasing depth and demonstrates a control by the sedimentological reservoir layering of the field. The data indicate that ali overgrowths in any one well cannot have precipitated from a single pore fluid. Overgrowths in shallow reservoir sandstones have precipitated from a higher δ18O fluid (basinal, δ18O + 5‰) than overgrowths in deeper reservoir sandstones (evolved meteoric, δ18O «= – 7 to +5‰). This long-term layering of diagenetic fluids also implies that quartz cernent can be formed from local sources: advective transport by warm fluids is not required. The greatest volume of quartz is inlerpreted to have precipitated at temperatures between 70°C and 110°C (2.3 to 3.7 km). Quartz cementation probably occurred most rapidly during periods of overpressure release. Volumes of quartz cement are not significamly different in shallower and deeper reservoir sandstones.
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Siliciclastic Diagenesis and Fluid Flow: Concepts and Applications
Research in the area of siliciclastic diagenesis has historically incorporated advances in related disciplines such as petrography and petrophysics, mineralogy, geochemistry, organic geochemistry, stratigraphy and basin analysis, and more recently, fluid flow. While the collection of papers in this publication covers a broad range of topics, an underlying theme is the importance of fluid flow in diagenetic processes. The mineralogy, texture and geochemistry of authigenic minerals provide constraints for fluid flow models, while formation waters provide modern snapshots of pore fluid evolution. Separated into two sections (Part I: Concepts and Part II: Applications), conceptual and practical applications are both represented.