Abstract The Volund Field lies in the Norwegian sector of the North Sea (Quad 24/9). This field produces from a ‘classic’ large-scale sandstone injection complex located in Lower Eocene strata. The sandstone reservoir has been injected into the lower permeability surrounding mudstones of the Sele and Balder formations and Hordaland Group to create an ‘intrusive trap’. The Volund Field consists of a deeper central unit of stacked sandstone sills, surrounded by shallower, steeper-dipping injected sandstone dykes, which make excellent reservoirs with consistently high porosity and permeability. Many of the steeply-dipping injected dykes appear to have excellent connectivity from the water leg through the oil leg and into the gas cap. The complex was identified on seismic data that exhibit a Class 3 amplitude versus offset (AVO) signature on the far-offset stack reflection seismic volume. The seismic data have been used to successfully locate horizontal production wells. Volund seismic geobodies have been extracted and incorporated into the reservoir geomodel to determine the geometry of the injectite features and to populate sands within the injection complex. Volund Field (estimated mean gross resource of 54 mmboe (million barrels oil equivalent)) is producing oil from four horizontal branches (end December 2012), with one water injector well, and has a common oil–water contact and gas–oil contact.

Abstract The understanding of the reservoir in the West Brae field in the North Sea has improved because of the incorporation of reprocessed seismic data into reservoir characterization and modeling. The field was discovered in 1975 with initial production in 1997 from two early Eocene turbidite sands in the Balder and Sele formations (Flugga sand member). Both turbidite sands are of good quality, with an average porosity of 30%, an average net-to-gross ratio of 85%, and permeability up to 7500 md. The field produces mainly black oil (22° API) with a dry gas cap and has two distinct oil-water contacts. A high-quality four-dimensional seismic data set was acquired in 2007, which was parallel processed with the 1993 baseline seismic data. These new data prompted a rebuild of the reservoir model to assess the potential for bypassed hydrocarbons. The West Brae model is the result of a multidisciplinary reservoir characterization study that has incorporated attributes from the 1993 reprocessed seismic survey into the static geologic model. The key to incorporating the three-dimensional seismic data into the reservoir model was an elastic simultaneous inversion attribute that clearly identified the good-quality reservoir sands. The integration of the new seismic data into the West Brae reservoir model has improved reservoir understanding by (1) providing a stratigraphic framework for the geomodel, (2) refining the depositional model, and (3) creating more consistency in the geostatistical distribution of reservoir properties in the model. Colocated cokriging of the well data and a “soft” seismic attribute volume (Poisson impedance) has helped reduce the uncertainty of sand distribution and the prediction of flow potential in the West Brae field. This case study has shown that using a multidisciplinary team (geophysics, geology, petrophysics, and reservoir engineering) and an integrated data set significantly reduces the uncertainty for a reservoir characterization study.

Abstract Fluvial incision and terracing produces a scale of architectural complexity that is often overlooked in geological interpretations and the construction of subsurface reservoir models. Results of a 2D seismic forward modelling study demonstrate the difficulties and limitations in resolving terraces seismically. We propose that terraced sequence boundaries fall readily into a subsurface data resolution gap between seismic and core to wireline log scale. Due to limitations in seismic resolution, sequence boundaries are usually interpreted as simple, single surfaces of erosion, for example at the bases of incised-valley fills. However, modern analogues show that sequence boundaries are in fact often compound in nature. The stratigraphic response to pulses of incision and aggradation in an incision-dominant phase can result in flights of stair-stepping terraces. In this paper we recognize two distinct architectural styles: attached and detached terrace flights. Their formation depends on the interplay between the magnitudes of incision versus aggradation. We suggest that terraced sedimentary architectures, the nature of the terrace-fill lithology, and any associated pedogenesis impacts upon mesoscale to macroscale reservoir permeabilities and therefore have implications for subsurface fluid flow. The existence of terraces, in conjunction with the inherent lack of temporal control in fluvial successions, may help to explain correlation difficulties often encountered and to an extent the compartmentalized production behavior of some fluvial hydrocarbon reservoirs.

Abstract The Song Hong-Yinggehai (SH-Y) and Qiongdongnan (Qi) basins together form one of the largest Cenozoic sedimentary basins in SE Asia. Here we present new records based on the analysis of seismic data, which we compare to geochemical data derived from cores from Ocean Drilling Program (ODP) Site 1148 in order to derive proxies for continental weathering and thus constrain summer monsoon intensity. The SH-Y Basin started opening during the Late Paleocene–Eocene. Two inversion phases are recognized to have occurred at c. 34 Ma and c. 15 Ma. The Qi Basin developed on the northern, rifted margin of South China Sea, within which a large canyon developed in a NE–SW direction. Geochemical and mineralogical data show that chemical weathering has gradually decreased in SE Asia after c. 25 Ma, whereas physical erosion became stronger, especially after c. 12 Ma. Summer monsoon intensification drove periods of faster erosion after 3–4 Ma and from 10–15 Ma, although the initial pulse of eroded sediment at 29.5–21 Ma was probably triggered by tectonic uplift because this precedes monsoon intensification at c. 22 Ma. Clay mineralogy indicates more physical erosion together with high sedimentation rates after c. 12 Ma suggesting a period of strong summer monsoon in the Mid-Miocene.

ABSTRACT The exceptional exposure of the margin of the Upper Devonian Miette (Frasnian) buildup in the Canadian Rockies provides a representative example of the sequence-stratigraphic framework of the Late Devonian for the subsurface of Alberta, Canada. The dominant eustatic sea level control during the Frasnian allows a comparison between the outcrop and subsurface buildups. A synthetic seismic section across the Miette buildup outcrop is used for calibrating and comparing the outcrop geometries and facies with seismic and log data across the subsurface Redwater reef complex. The results of this case study illustrate that if the seismic geometries and characteristics are well calibrated with detailed geology, even lower-frequency seismic data can be used to predict platform architecture and large-scale stratigraphic sequences. The outcrop-derived sequence-stratigraphic framework is the basis for the impedance model for constructing synthetic seismic sections at various frequencies. The synthetic sections document the seismic characteristics of the platform, margin, and basinal areas. Two types of seismic-scale geometries are also found in the subsurface Redwater reef complex: a rimmed platform margin and clinoforms of a prograding platform. The iterative interpretation of seismic data and well logs with outcrop data results in a reinter-pretation of the platform architecture of the Redwater reef complex in the subsurface. This reinterpretation is based on the identification of four sedimentological phases in a platform construction and the six third-order depositional sequences in outcrop that can be correlated to facies in core and the geometries observed on the seismic data from the Redwater reef complex. Phase I is a regional carbonate ramp/platform and is characterized by a ramp platform architecture. Phase II is characterized by the retro-gradation of the platform and the initiation of buildups and can contain low-angle progradation in the retrograding platforms. Phase III is characterized by platform aggradation and basin starvation. This phase generates a steep-rimmed platform margin. Phase IV is characterized by basin infill followed by platform progradation. These four phases form in a second-order sea level cycle, in which Phases I–III are deposited during the transgressive part and Phase IV during the regressive part of the cycle. Such a coherent model can enhance both exploration and development and can be used or modified to fit analogous areas where data is lacking. Because this second-order sea level change in the Frasnian is mostly eustatic in nature, the resulting platform architecture is expected to be found in other age-equivalent isolated carbonate buildups in Canada or around the world.