Paralic environments, deltas, estuaries and shoreline-shelf systems respond sensitively to changes in sea-level and sediment supply, commonly by shifts in facies belts across sequence stratigraphic surfaces. As a result, they are often interleaved in highly layered successions. Layering and a wide range of associated sandbody types control the distinctive nature of paralic oil and gas fields. Layering results in stacked reservoirs. Thick extensive sandstones have structurally defined spill points, large aquifers and good reservoir properties. Such sands have high recovery, good reservoir performance and form primary completion targets. By contrast, thin, laterally restricted, isolated sandstones have low recovery factors and poor performance. Each isolated sand may have its own hydrocarbon contacts and a distinct outline that reflects both structural and stratigraphic trapping. Such sands form secondary completion targets. Fault compartmentalization is a recurring risk. Sealing faults increase the number of reservoir compartments and may decrease performance and recovery. They can also generate traps. Sedimentology is pivotal in describing heterogeneity in paralic reservoirs at all scales. Established techniques are likely to be complemented in the future by forward stratigraphic modelling, integration with palynology and more studies of surveillance data to show how sedimentological variability controls fluid movement in real reservoirs.
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Sedimentology of Paralic Reservoirs: Recent Advances
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Paralic reservoirs reflect a range of depositional environments including deltas, shoreline-shelf systems and estuaries. They provide the backbone of production in many mature basins, and contribute significantly to global conventional hydrocarbon production. However, the range of environments, together with relative sea-level and sediment supply changes, result in significant variability in their stratigraphic architecture and sedimentological heterogeneity, which translates into complex patterns of reservoir distribution and production that are challenging to predict, optimize and manage.
This volume presents new research and developments in established approaches to the exploration and production of paralic reservoirs. The 13 papers in the volume are grouped into three thematic sections, which address: the sedimentological characterization of paralic reservoirs using subsurface data; lithological heterogeneity in paralic depositional systems arising from the influence of tidal currents; and paralic reservoir analogue studies of modern sediments and ancient outcrops. The volume demonstrates that heterogeneity in paralic reservoirs is increasingly well understood at all scales, but highlights gaps in our knowledge and areas of current research.