In a sedimentological sense a fluvial to tidal transition zone can be defined in rivers as a zone that separates the upstream fluvial from the downstream estuarine zone. Characteristic sedimentary structures within this zone are notoriously difficult to recognize. This study demonstrates the influence of tidal modulation within the most proximal part of the fluvial-tidal transition zone (i.e. the 'backwater zone') of an ancient fluvial system. Criteria have been established to differentiate between purely fluvial facies and those modulated by tidal energy. The stratigraphic interval from which the data were derived is the Lourinhã Formation (Late Jurassic) of the Lusitanian Basin, WesternPortugal. An analysis of sedimentary features at four key localities has identified a temporal spectrum of tidal influence ranging from the daily modulation of fluvial flows to the effects of tidal bore passage. A combination of quantitative and qualitative data reveals systematic changes in the internal architecture of dune-scale bedforms deposited in a channel-floor setting. The key co-occurring features are: (i) increasing-decreasing organic particle concentration; (ii) increasing-decreasing bottomset thickness; (iii) increasingdecreasing foreset dip and shape (from convex to concave); and (iv) increasingdecreasing brinkpoint height. Collectively, these features are interpreted as having been produced by successive fluctuations in flow regime conditions from lower (during flood tidal retardation) to higher (during ebb tidal drawdown) current velocities. Bedforms showing these features occur in both meandering fluvial channels and straighter distributary systems. In addition, several examples of a specific type of stepped erosion surface and draping sediment have been recognized, the interpretation of which strongly suggests generation by the passage of tidal bores. If this interpretation is correct, then it represents one of the first published examples of tidal bore propagation in ancient fluvial systems. Palaeoclimatic evidence (cellular analysis of woody tissue, palaeosol character and plate reconstruction) indicates a warm, seasonal, winter wet to summer dry climate during deposition of the Lourinhã Formation. From this evidence it is suggested that tidal modulation and tidal bore effects are more likely to develop in the 'dry season', when fluvial flow in the main river channels was reduced.

The c. 700 m thick succession of continental–brackish‐marine deposits forming the Lourinhã Formation, cropping out along the coast of western Portugal between Baleal and Santa Cruz, has been correlated using laterally persistent shelly marker beds. Three shelly units record the episodic establishment of relatively short‐lived, brackish‐marine embayments, transgressing from the southwest, onto a low‐lying coastal plain. The succession displays systematic changes in facies types and stacking patterns reflecting differences in fluvial style, bedload character and palaeontological content. Based on these observations, four new members for the Lourinhã Formation are proposed: the Sáo Bernardino, Porto de Barças, Areia Branca and Ferrel members. New biostratigraphical data indicate that the Lourinhã Formation is Late Kimmeridgian to earliest Early Tithonian in age. This age has also been obtained from the underlying mixed carbonate and clastic deposits of the Abadia Formation at Consolação. As a result, these latter sediments are now re‐assigned to the Alcobaça Formation, a lithostratigraphical term currently in use in other areas of the Lusitanian Basin. Improved regional mapping of the Lourinhã Formation has established a new sub‐basin within the western parts of the Lusitanian Basin. This sub‐basin, now named the Consolação Sub‐basin, is bounded to the east by the Lourinhã–Caldas de Rainha (L–C) fault zone and to the west by the Berlengas Horst. Copyright © 2013 John Wiley & Sons, Ltd.

Analogues, especially outcrop analogues, have played a central role in improving understanding of subsurface reservoir architectures. Analogues provide important information on geobody size, geometry and potential connectivity. The historical application of outcrop analogues for understanding geobody distributions in reservoirs is reviewed, from the pioneering work of the 1960s to the high-tech virtual outcrop methodologies of today. Four key types of analogue data are identified: hard data, which describe the dimensions and geometry of the geobody; soft data, which describe the conceptual relationships between different geobody types; training images, which record the dimensions, proportions and spatial relationship; and analogue production data, which are taken from direct subsurface production analogues. The use of these different data types at different stages of the geomodelling workflow is discussed and the potential sources of error considered. Finally, a review of geobody and analogue studies in different clastic environments is discussed with reference to selected previous work and the range of papers in the current volume.Over the last 30 years, computer-based, geocellular models have become a routinely used tool for understanding subsurface reservoirs (Budding & Inglin 1981; review in Keogh et al. 2007). Such models are typically built to aid field development and reservoir management business decisions, but also serve the purpose of integrating disparate scales and types of subsurface data, and visualizing complex three-dimensional (3D) distributions of rocks and fluids. Since the application of early modelling tools, to the present day, it has been common practice to supplement sparse subsurface datasets (e.g. wells and seismic) with data and concepts derived from reservoir analogues. The intention of this process is to generate more accurate representations of the subsurface than would otherwise be possible. Considerable effort has been expended in recent years by industry and academia on the description of reservoir analogues for this purpose. This paper examines the challenges inherent in selection and application of appropriate analogue data, particularly quantitative datasets, during construction of geological models.The most commonly used type of analogue is the outcrop, where information on geometric data that are limited in the subsurface is more readily available in cliff sections. Analogues may also include subsurface data but this is less common. This aspect is considered briefly in this review. The perspective on the application of analogues as discussed here is with regard to sedimentology and stratigraphy applied to hydrocarbon reservoir analysis, and the insights that 3D facies models bring to the distribution of petrophysical properties that control hydrocarbon flow. The discussion is based on clastic systems, but many of the aspects described are equally as applicable to carbonates, although they are not discussed explicitly here. Other branches of subsurface modelling, no...

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Production from the Halten Terrace hydrocarbon province (Mid-Norwegian shelf) is mainly from heterolithic siliciclastic successions as well as diagenetically altered sandstones. Eight hydrocarbon fields are currently in production, which produce c . 840 000 BBL oil equivalent per day, with several new fields expected to come on stream in the next decade. This paper is an introduction to a thematic set on the characterization and modelling of heterolithic reservoirs and focuses on the three main types of heterogeneity: (1) heterolithic facies, (2) faulting and (3) diagenesis. Challenges vary according to field setting: shallow (1–3 km burial depth), deep (3–5 km) or very deep (currently up to 5.6 km). Water depths vary from 200 m to 500 m. Heterolithic sedimentary packages are composed of shale or siltstone layers intercalated with clean, but often thin, sandstone layers of varying lateral extent. These were deposited in Lower Jurassic tide-influenced or tide-dominated deltaic and estuarine environments along the margin of a shallow seaway. Hydrocarbon traps are formed by faulted and rotated fault blocks created during rifting. Faulting of these heterolithic facies is a critical parameter for fluid flow, with fault transmissibility and fault position often difficult to determine. Complex patterns of diagenetic cementation are an additional aspect of heterogeneity in the deeply buried reservoirs, such as the Smørbukk and Kristin fields. However, grain coatings of chlorite, illite/chlorite and illite have prevented or hindered the development of quartz overgrowths and allowed the preservation of anomalously high porosity and permeability. Modelling and assessing the impact of these reservoir uncertainties has included development of novel tools and methods, leading to a much-improved level of understanding, better prediction of recoverable reserves and significantly increased recovery factors.

Tide-dominated deltas have an inherently complex distribution of heterogeneities on several different scales and are less well-understood than their wave-dominated and river-dominated counterparts. Depositional models of these environments are based on a small set of ancient examples and are, therefore, immature. The Early Jurassic Gule Horn Formation is particularly well-exposed in extensive sea cliffs from which a 32 km long, 250 m high virtual outcrop model has been acquired using helicopter-mounted light detection and ranging (LiDAR). This dataset, combined with a set of sedimentological logs, facilitates interpretation and measurement of depositional elements and tracing of stratigraphic surfaces over seismic-scale distances. The aim of this article is to use this dataset to increase the understanding of depositional elements and lithologies in proximal, unconfined, tide-dominated deltas from the delta plain to prodelta. Deposition occurred in a structurally controlled embayment, and immature sediments indicate proximity to the sediment source. The succession is tide dominated but contains evidence for strong fluvial influence and minor wave influence. Wave influence is more pronounced in transgressive intervals. Nine architectural elements have been identified, and their internal architecture and stratigraphical distribution has been investigated. The distal parts comprise prodelta, delta front and unconfined tidal bar deposits. The medial part is characterized by relatively narrow, amalgamated channel fills with fluid mud-rich bases and sandier deposits upward, interpreted as distributary channels filled by tidal bars deposited near the turbidity maximum. The proximal parts of the studied system are dominated by sandy distributary channel and heterolithic tidal-flat deposits. The sandbodies of the proximal tidal channels are several kilometres wide and wider than exposures in all cases. Parasequence boundaries are easily defined in the prodelta to delta-front environments, but are difficult to trace into the more proximal deposits. This article illustrates the proximal to distal organization of facies in unconfined tide-dominated deltas and shows how such environments react to relative sea-level rise.

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The first sandstone unit of the Esdolomada Member of the Roda Formation (hereafter referred to as 'Esdolomada 1') was formed by a laterally-migrating, shelf tidal bar. This interpretation is based on detailed mapping of the bedding surfaces on the digital terrain model of the outcrop built from light detection and ranging data and outcrop photomosaics combined with vertical measured sections. The Esdolomada 1 sandbody migrated laterally (i.e. transverse to the tidal currents) towards the south-west along slightly inclined (1.6°to 4.6°) master bedding surfaces. The locally dominant tidal current flowed to the northwest. This current direction is indicated by the presence of stacked sets of highangle (average 21°) cross-stratification formed by dunes that migrated in this direction, apparently in an approximately coast-parallel direction. The tidal bar contains sets and cosets of medium-grained cross-stratified sandstone that stack to reach a thickness of about 5AE5 m. Individual cross-bed sets average about 50 cm thick (with a range of 10 to 70 cm) and have lengths of ca 130 to 250 m in a direction perpendicular to the palaeocurrent. Set thickness decreases in the direction of migration, towards the south-west, and the degree of bioturbation increases, so that the cross-bedded sandstones gradually change into highly bioturbated finer-grained and thinner-bedded sandstones lacking any crossstratification. The rate of thinning of individual dune sets as they are traced down any obliquely-accreting master surface is some 40 cm per 100 m (0AE004) for the older, thicker sandstones, whereas the younger, thinner beds thin at a rate of 15 cm over 100 m (0AE0015). The tidal bar has a sharp base and top and is encased in finer-grained bioturbated, marine sandstones. The Esdolomada bar crest was oriented north-west to south-east, parallel to the tidal palaeocurrents and to the nearby palaeoshoreline, but built by lateral accretion towards the south-west. Lateral outbuilding generated a flat-topped bar with a measured width of about 1700 m, and a preserved height of 5AE5 m. The bar, disconnected from a genetically related south-westward prograding delta some 2 km to the north-east, developed during the transgressive phase of a sedimentary cycle. The tidal bar was most probably initiated as a delta-attached bar at the toesets of the delta front and during transgression evolved into a detached tidal bar.