Allard W. Martinius

Sedimentology of the heterolithic and tide-dominated tilje formation (Early Jurassic, Halten Terrace, Offshore Mid-Norway)

The Early Jurassic Tilje Formation on the Halten Terrace, offshore mid-Norway, was deposited in a relatively narrow but long seaway connecting the Boreal Ocean in the north and the Tethys Ocean in the south. Sediments of the Tilje Formation in the Smorbukk and Heidrun Fields have been classified into ten facies associations. Many of the lithofacies are mud-rich and typified by strong grain-size contrasts. In addition, all but two of the facies associations are tidally influenced or dominated. As a result, 80% of the total rock volume consists of very heterolithic sediments characterised by rapidly alternating grain-size changes between mudstone or siltstone and fine-to medium-grained sandstone. In the Tilje Formation, the recognition and interpretation of heterolithic facies is crucial to understanding the depositional conditions and stratigraphic architecture. The classification scheme and the associated facies breakdown in cored wells served to define two successive conceptual depositional models that are placed in a sequence stratigraphic framework. The lower part of the Tilje Formation (T1 and most of T2) are envisaged to have formed in response to base-level fall, creating a series of low-relief valleys, and subsequent base-level rise resulting in the formation of a tide- and wave-dominated estuarine system. The upper part of the Tilje Formation (top of T2 to T6) is interpreted to have formed as a tide- and fluvial-dominated delta-like system. These two contrasting depositional styles resulted in different three-dimensional facies architectures, relative facies proportions, and facies stacking patterns, which have implications for reservoir model-building methods.

Reservoir challenges of heterolithic tidal sandstone reservoirs in the Halten Terrace, mid-Norway

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.

Ranking of stochastic realizations of complex tidal reservoirs using streamline simulation criteria

This study concerns the modelling of complex tidal heterogeneities found in the Lower Jurassic Tilje Formation offshore mid-Norway. The Tilje Formation is characterized by tidal channels, tidal bars (shoals), tidal flats and deltaic deposits. The lithofacies associations have been modelled as large-scale objects with a wide range of shapes (channels, sheets and lobes). In addition small-scale models of the internal bedding structure have been generated in order to calculate effective permeability values at appropriate modelling scales. In order to assess the influence of the static input factors on recovery predictions, several production response variables were recorded for each of the 120 realizations generated. These include: streamline densities, breakthrough time measured in movable pore volume injected, pore volume tracer injected at 50% and 95% tracer fraction in the producer, and recovery factor of movable pore water at 95% tracer fraction in the producer. For this purpose we used a streamline reservoir simulator (Frontsim) with a tracer option (single-phase flow simulations). By using analysis of variance, we identified the following parameters which have the largest influence on single-phase fluid flow: (1) dimension of large-scale bar objects; (2) effective permeabilities of marginal (background) facies; and (3) interaction effects between bar objects and background permeabilities. In addition, the effective permeability values of the marginal facies are highly controlled by certain thresholds in mud content.

The application of outcrop analogues in geological modelling: a review, present status and future outlook

Abstract 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.

Uncertainty analysis of fluvial outcrop data for stochastic reservoir modelling

Uncertainty analysis and reduction is a crucial part of stochastic reservoir modelling and fluid flow simulation studies. Outcrop analogue studies are often employed to define reservoir model parameters but the analysis of uncertainties associated with sedimentological information is often neglected. In order to define uncertainty inherent in outcrop data more accurately, this paper presents geometrical and dimensional data from individual point bars and braid bars, from part of the low net:gross outcropping Tortóla fluvial system (Spain) that has been subjected to a quantitative and qualitative assessment. Four types of primary outcrop uncertainties are discussed: (1) the definition of the conceptual depositional model; (2) the number of observations on sandstone body dimensions; (3) the accuracy and representativeness of observed three-dimensional (3D) sandstone body size data; and (4) sandstone body orientation. Uncertainties related to the depositional model are the most difficult to quantify but can be appreciated qualitatively if processes of deposition related to scales of time and the general lack of information are considered. Application of the N0 measure is suggested to assess quantitatively whether a statistically sufficient number of dimensional observations is obtained to reduce uncertainty to an acceptable level. The third type of uncertainty is evaluated in a qualitative sense and determined by accurate facies analysis. The orientation of sandstone bodies is shown to influence spatial connectivity. As a result, an insufficient number or quality of observations may have important consequences for estimated connected volumes. This study will give improved estimations for reservoir modelling.

Multiscale geological reservoir modelling in practice

Abstract Geological systems exhibit variability and structure at a wide range of scales. Geological modelling of subsurface petroleum reservoirs has generally focused on the larger scales, driven by the types of measurement available and by computation limitations. Implementation of explicitly multiscale models of petroleum reservoirs is now realistically achievable and has proven value. This paper reviews the main approaches involved and discusses current limitations and challenges for routine implementation of multiscale modelling of petroleum-bearing rock systems. The main questions addressed are: (a) how many scales to model and upscale; (b) which scales to focus on; (c) how to best construct model grids; and (d) which heterogeneities matter most? The main future challenges identified are the need for improved handling of variance and more automated construction of geological and simulation grids.

Integration of subsurface applications to develop a dynamic stochastic modeling workflow

Building stochastic models in a preproduction phase of field development is crucial for accurate horizontal well positioning in the Sincor field (Orinoco heavy-oil belt, Venezuela), formed by highly permeable unconsolidated fluvial and deltaic sands of the Oficina Formation and containing low-gravity oil (average 8.3 API). A multidisciplinary approach to drill the initial approximately 250 horizontal production wells has proven useful to field management. Geomodeling is used to evaluate well pattern development plans; calculate full-field production percentile profiles; and evaluate uncertainties in water production, well production potential, and cluster performance. Data from vertical observation wells (full well-logging suite) and deviated wells (to investigate the stratigraphy away from the vertical well) are used to characterize reservoir architecture. Three-dimensional seismic data, including seismic data inverted into acoustic impedance, are used to construct structure maps and shale probability maps. The integrated and interpreted information is used to position horizontal wells deterministically in a cluster-type (group of wells radiating out from a central point in a 3.2 1.6-km [2 1-mi] production area) development pattern and serves as input to stochastic reservoir models that are conditioned to vertical well observations and the shale probability maps. Ten realizations are used to estimate the uncertainty range of net-to-gross in the proposed horizontal well trajectories. To ensure a stable model, the average of these 10 realizations is used as a trend to generate one stochastic petrophysical model that is subsequently used for flow simulation. Based on the results, and in combination with the confidence in the interpreted geological data (for example, distribution of areas with a net sand thickness above a minimum), proposed horizontal wells are accepted or rejected.

From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin

Preface vii Dedication to John Gjelberg, Michael Talbot and Trevor Elliott xi Generic autogenic behaviour in fluvial systems: lessons from experimental studies 1 G. Postma Climatic and tectonic controls on Triassic dryland terminal fluvial system architecture, central North Sea 19 T. McKie Late Triassic to Early Jurassic climatic change, northern North Sea region: impact on alluvial architecture, palaeosols and clay mineralogy 59 J.P. Nystuen, A.V. Kjemperud, R. Muller, V. Adestal and E.R. Schomacker Applying accommodation versus sediment supply ratio concepts to stratigraphic analysis and zonation of a fluvial reservoir 101 A.W. Martinius, C. Elfenbein and K.J. Keogh Investigating the autogenic process response to allogenic forcing: experimental geomorphology and stratigraphy 127 W. Kim, A. Petter, K. Straub and D. Mohrig The autostratigraphic view of responses of river deltas to external forcing: a review of the concepts 139 T. Muto and R.J. Steel Autogenic process change in modern deltas: lessons for the ancient 149 C. Olariu Morphodynamic modelling of wave reworking of an alluvial delta and application of results in the standard reservoir modelling workflow 167 M.M. Hillen, N. Geleynse, J.E.A. Storms, D.J.R. Walstra and R.M. Groenenberg Sedimentation at the Jurassic Triassic boundary, south-west Barents Sea: indication of climate change 187 A. Ryseth Halten Terrace Lower and Middle Jurassic inter-rift megasequence analysis: megasequence structure, sedimentary architecture and controlling parameters 215 R. Ravnas, K. Berge, H. Campbell, C. Harvey and M. Norton Updated depositional and stratigraphic model of the Lower Jurassic Are Formation, Heidrun Field, Norway 253 C. Thrana, A. Naess, S. Leary, S. Gowland, M. Brekken and A. Taylor Depositional dynamics and sequence development in a tidally influenced marginal marine basin: Early Jurassic Neill Klinter Group, Jameson Land Basin, East Greenland 291 J.M. Ahokas, J.P. Nystuen and A.W. Martinius Eustatic, tectonic and climatic controls on an early syn-rift mixed-energy delta, Tilje Formation (Early Jurassic, Smorbukk field, offshore mid-Norway) 339 A.A. Ichaso and R.W. Dalrymple Tectonic influence on the Jurassic sedimentary architecture in the northern North Sea with focus on the Brent Group 389 A. Folkestad, T. Odinsen, H. Fossen and M.A. Pearce Mesozoic and Cenozoic basin configurations in the North Sea 417 E.M. Jarsve, J.I. Faleide, R.H. Gabrielsen and J.P. Nystuen 3D forward modelling of the impact of sediment transport and base level cycles on continental margins and incised valleys 453 D. Granjeon Tectonic control on sedimentation, erosion and redeposition of Upper Jurassic sandstones, Central Graben, North Sea 473 J.P. Wonham, I. Rodwell, T. Lein-Mathisen and M. Thomas The Garn Formation (Bajocian-Bathonian) in the Kristin Field, Halten Terrace: its origin, facies architecture and primary heterogeneity model 513 C. Messina, W. Nemec, A.W. Martinius and C. Elfenbein Channel development in the chalk of the Tor Formation, North Sea: evidence of bottom current activity 551 M. Gennaro and J.P. Wonham MassFLOW-3DTM as a simulation tool for turbidity currents: some preliminary results 587 R. Basani, M. Janocko, M.J.B. Cartigny, E.W.M. Hansen and J.T. Eggenhuisen The Ormen Lange turbidite systems: sedimentary architectures and sequence structure of sandy slope fans in a sediment-starved basin 609 R. Ravnas, A. Cook, K. Engenes, H. Germs, M. Grecula, J. Haga, C. Harvey and J.A. Maceachern Unravelling the nature of deep-marine sandstones through the linkage of seismic geomorphologies to sedimentary facies the Hermod Fan, Norwegian North Sea 647 B.K.L. Bryn and M.A. Ackers Index 677

Lithofacies characterization of fluvial sandstones from outcrop gamma-ray logs (Loranca Basin, Spain): the influence of provenance

Natural gamma spectral (NGS) log motifs and cluster analysis were used to characterize outcropping sandstone bodies formed in braided and high-sinuosity streams of the Tertiary Tórtola fluvial system of the Loranca Basin (Spain). Five coarse-grained lithofacies comprise these deposits and determine distinct NGS log motif. Cross-plots and cluster analysis of NGS log data of the lithofacies suggest three distinct clusters. These clusters reflect distinct values for sandstones with small sets of ripple lamination, cross-stratification, and conglomerates and pebbles. Ripple-laminated sandstones show the most variability in NGS signature, whereas conglomeratic sandstones show the most uniform signature. Such cluster analysis may be used to assign NGS log data points of unknown origin to a specific fluvial lithofacies under conditions of equal rock provenance and diagenetic history. A sedimentaclastic (i.e. sedimentary parent rock) origin of sediments appears to be the main control on detrital composition that, in turn, varies with grain size.

Basin analysis and sequence stratigraphy of the synrift Tilje Formation (Lower Jurassic), Halten terrace giant oil and gas fields, offshore mid-Norway

The stratigraphic organization of early synrift clastic successions is controlled by the rates of tectonic subsidence and the growth of the master faults, which, coupled with eustatic base level change, control the generation of accommodation. The 100- to 300-m (328- to 984.2-ft)-thick, highly heterolithic Lower Jurassic upper Are and Tilje succession (Halten terrace, offshore Norway) represents an example of ancient synrift deposits that accumulated within a north–northeast-south–southwest-oriented structurally controlled embayment where sedimentation was strongly influenced by tidal currents but with significant river influence and minor wave action, except in exposed distal locations. The shallowing-upward, deltaic Tilje succession was deposited near the lowstand shoreline. The Tilje Formation consists of two tabular second-order sequences, each of which overlies structurally influenced sequence boundaries (SB2 and SB3 in local terminology) associated with rift-related tectonic pulses. The first pulse led to formation of SB2 (shallow incision into the Are Formation) and caused a regional geomorphological change of the basin from an open, wave-dominated setting (upper Are Formation) to a funnel-shaped, tide-dominated setting (Tilje Formation), in which the lower sequence 2 accumulated. Sequence 3 rests erosively on sequence 2 and is characterized by proximal tidal deposits showing at least two main oblique to axial fluvial input points (north–northwest and northeast), with an increase in wave influence and deepening toward the south. Local rapid subsidence of elongated, narrow hanging wall basins exerted a subtle control on the succession thickness and distribution of tidal–fluvial distributary channels. The overall tabular geometry and internal architecture of the Tilje Formation is less complex than that of other tidal successions worldwide, showing lateral and vertical compartmentalization of the best tidal–fluvial sandstone reservoirs.