ALBERT

Description: 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 Åre 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 Åre Formation) and caused a regional geomorphological change of the basin from an open, wave-dominated setting (upper Åre 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.

Description: Current recovery from the Statfjord Group in the majority of the fields on the Tampen Spur is less than 50%. A contributing factor to this is an incomplete understanding of multiscale heterogeneities, their distributions within a range of fluvial geobodies and their lateral extent and morphology in inter-well areas. Sedimentary heterogeneities have been modelled, together with petrophysical parameters, at a variety of scales. The modelled properties at a given scale were upscaled to the next level of heterogeneity, thus better honouring effective property values. The use of outcrop analogues is still a key tool for understanding facies relationships and the stratigraphic development of subsurface hydrocarbon-bearing reservoirs. The Lourinhã Formation, Portugal, was used as an analogue to collect both qualitative and quantitative data consistently following a three-phase workflow to capture data at various scales of heterogeneity. Traditional field data collection techniques have been supplemented with the collection of LiDAR data. A digital workflow utilizing interlinked datasets facilitates rapid data analysis and better data visualization with results that are more easily utilized in multiscale modelling studies. These scaled models were used to increase our understanding of the effect on flow of lithofacies and facies association distributions together with internal architectural elements and heterogeneities.

Description: 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.

Description: 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. Tarald Svanes is discipline leader in subsurface uncertainty treatment at Statoil. Since 1990, he has worked with integrated, three-dimensional reservoir modeling and flow simulation, applying advanced geostatistical techniques. Currently, one of his main focuses is to reduce uncertainty in field prognoses by integrating production data into the reservoir characterization process. Svanes holds an M.S. degree in physics from the Norwegian Technical Institute in Trondheim. At Statoil, he has worked with various aspects of reservoir technology, ranging from research to operational field management, both in the North Sea and internationally.Allard W. Martinius has an M.Sc. degree from the University of Utrecht and a Ph.D. from Delft University. He joined Statoil in 1996 and spent his first three years at the research center in Trondheim, working on reservoir characterization and modeling of heterolithic tidal res ervoirs. He subsequently joined Sincor in Venezuela as a field development geologist. He returned to Statoil's research center in 2002 to lead a reservoir and uncertainty modeling research group. His main interests are in siliciclastic sedimentology, stratigraphy, reservoir characterization, and geomodeling. JoAnn Hegre received an M.Sc. degree from Tulane University (U.S.A.). She is currently head of geological research at Total's Geoscience Research Center in London. She has specialized in the field of geomodeling and reservoir characterization for the past seven years. Before taking up this position, she spent three years at Sincor, where she was in charge of geomodeling and volume calculations. Jean-Pierre Maret joined Total in 1982 and worked as field geologist and team leader at the head office in Paris until 1993. During that period, he spent two years in Abu Dhabi and four years in Buenos Aires. Subsequently, he became exploration manager for Total Myanmar in Yangon, where he spent four years; after which, he was in charge of field evaluation studies and exploration coordinator for southeast Asia. Recently, he worked for two years in Venezuela on the Sincor field, where he was responsible for the geology and geophysics studies and operations. Maret is currently the coordinator for the Americas for Total. Rune Mjøs is lead geologist for the Snorre field, northern North Sea, which he joined in 2002. Prior to that, he was seconded to the Sincor field in Venezuela as senior sedimentologist in the full-field evaluation team. He has been with Statoil since 1991 and has worked as exploration and production geologist on various technical evaluation projects. His main interest is in sedimentology and genetic stratigraphy. From 1997 to 1999, he was Statoil's advisor in sedimentology. Rune has a Cand. Scient. degree from the University of Bergen. After obtaining his degree, he worked for two years as exploration geologist for Norsk Hydro and subsequently, four years as scientist at Rogaland Research Institute. He has published articles on sedimentology, diagenesis, and sequence stratigraphy both for petroleum exploration and production purposes. Juan Carlos Ustáriz Molina, a petroleum engineer from the Universidad Central de Venezuela, obtained his degree in 1994. Since then, he has worked for Mares de Venezuela (MARAVEN) and Petróleos de Venezuela S. A. (PDVSA) in operations and reservoir simulation. In 1998, he started to work for Pennzoil in western Venezuela as a geomodeler and joined Sincrudos de Oriente (SINCOR) as geomodeler in 2000.