EAGE Research Workshop - From Seismic Interpretation to Stratigraphic and Basin Modelling, Present and Future

Seismic interpretation provides basic, and sometimes sparse, information about the architecture of a basin in terms of stratigraphic surfaces, structural discontinuities at Present, and hypotheses on the sedimentological history.

Stratigraphic modelling provides a quantified description of the basin architecture and lithology distribution as a function of time, accordingly to hypotheses on paleogeography, sediment flux at the basin boundaries, subsidence and eustatism. The stratigraphic model produced in this way is supposed to be consistent with our knowledge of sedimentary processes.

In this paper, we introduce a methodology to use stratigraphic modelling as a validation tool for seismic interpretation. It consists in running and calibrating a stratigraphic model according to the seismic interpretation, running synthetic seismic on the stratigraphic model obtained in this way, and comparing the synthetic seismic to the real one.

The workflow workflow presented here overcomes the problem of the difference of resolution between the basin stratigraphic model and the resolution required for running the seismic modelling. It shows the sensitivity of the seismic image to subtle features of the geologic model. It also gives us some keys to better understand the link between geologic features and the way they are imaged by the seismic.

Interpretation of 3-D seismic data from Central Saudi Arabia allowed mapping of the Permo-Carboniferous Unayzah formation’s aeolian sand deposits and fluvial channels. These types of depositional environments have been frequently associated with better reservoir-quality sandstones within Saudi Arabia. The depositional setting of the Unayzah reservoirs can be highly variable and range from; glacial, to lacustrine, to meandering fluvial, to aeolian, to braided stream. Seismic amplitude data was instrumental in mapping a truncation of the upper Unayzah reservoir against the overlying Pre-Khuff Unconformity. The use of seismic attributes such as coherence and curvature indicated the existence of faulting and a fluvial channel network at the top of the Unayzah Formation. The integration of well and seismic amplitude data, via acoustic impedance inversion, revealed the direction of potentially higher porosity fairways within the channel system.

A sequence stratigraphic interpretation system (OpendTect SSIS) is developed that allows seismic data to be studied in the chrono-stratigraphic domain. The Wheeler-transformed (flattened) data provides new insights in the spatial distribution and timing of sedimentary deposits and allows data to be visualized in a completely new way, i.e. along stratigraphic events at (sub-)seismic resolution. The combined analyses of various volumes, (e.g. porosity, seismic facies segmentation, spectral decomposition, etc.) in both the Wheeler transformed and structural domain reveals geometries and patterns that would otherwise be difficult to interpret in the structural domain alone. Transgressive - regressive trends and lap-out patterns are used to do a complete systems tracts interpretation, while the combination of various volumes -visualized in both domains- give insight in the facies distribution and their shift in time and space.
Finally, the possibilities of incorporating the chrono-stratigraphic results in different disciplines will be discussed as well as our perspective on how to improve the analyses by incorporating additional data.

The sequence stratigraphic modelling study from the offshore Cenozoic Tarfaya basin located between the Canary Islands and Morocco is mainly performed with seismic and well data in order to assess different possible exploration areas. Results of this study confirm the importance of rapid changes from uplift to subsidence on the Atlantic passive continental margin for the evolution of accommodation space in time. A tectonic active phase in the onshore part of the Aaiun-Tarfaya basin during the Eocene/Oligocene is witnessed by several hiatuses on the shelf and pronounced mass transport complexes in the basin. Seismic interpretation and numerical forward modelling indicate decreased preservation of sediments during these times, possibly because of a combination of multiple slumping and reduced sedimentary input into the system. Input data for sequence stratigraphic forward modelling are calibrated with sedimentary flux rates derived from a GIS-based analysis of the hinterland. The modelled sedimentation rates reflect the regional climatic and tectonic evolution during the Cenozoic in the study area. Especially after a turnover from greenhouse to icehouse conditions in Oligocene times (Séranne, 1999), an increased sedimentary input into the exploration area is observed in the seismic interpretation and verified within the course of sequence stratigraphic modelling.

When available, seismic data is a key input for basin characterization.However, seismic data are sometimes sparse, with locally poor quality, and limited resolution. Consequently, seismic interpretation provides information which is often uncertain and quantitatively not precise enough.
In an other hand, process based stratigraphic modelling consists in the forward simulation of the sedimentary processes which formed the basin architecture over geolocical times. Stratigraphic modelling basically provides the same type of deliverable as the seismic interpretation, namely a description of the basin architecture : major stratigraphic discontinuities and lithology distribution. The output stratigraphic model is precisely quantified everywhere in the basin, and is supposed to be geologically consistent. Here, the uncertainty on the final basin model is related to the parameters used for the numerical simulations.
These two approaches provide, through different ways, complementary information of the same nature. Integrating them in the same basin characterization workflow will obviously decrease the uncertainty on the final geological model.
In this paper, we describe how we propose to integrate the two approaches in a unique workflow, in order to provide a unified description of the basin, which is both consistent with the seismic data and with a process-based stratigraphic modelling technique.

High success rates in the exploration for oil and gas can be accomplished by incorporating best practice strategies in estimating the geological uncertainties from seismic data and geological models. A tight coupling of the seismic information and hydrocarbon migration modeling may allow for a consistent handling of uncertainties throughout the analysis. Seismic uncertainties include velocities used for depth conversion, the positioning of structural interpretations - including faults - and assigning (flow) properties from seismic attributes. Needed output from the seismic uncertainty analysis could be provided as uncertainty fields that may be used as input to hydrocarbon migration modeling.

The non-linearity of the hydrocarbon migration process, including flow-path selection and trap phase filtering, frequently require that local uncertainties are addressed in more detail. These uncertainties may require high-resolution seismic analyses in order to be further resolved. The structural interpretation is of particular importance to accumulation uncertainties, and fault juxtaposition and carrier dip direction uncertainty estimations can improve phase prediction estimates in exploration prospects.
It is therefore suggested that an improved best practice for exploration for oil and gas should include a tight coupling of the handling of uncertainties from seismic in hydrocarbon migration modeling.

Integrated basin simulators have limited tools to address autochthonous and allochthonous salt deformation. Currently, basin simulators must either geometrically reconstruct the salt thickness through time or assume that the salt thickness history is the same as the present day salt thickness. In the case that the salt is reconstructed geometrically, there is no direct coupling between sediment density and salt deformation. In the case that the present day salt thickness is held constant through time, the assumption is made that basement accommodates changes in sediment thickness. In both these cases, simulation results can be misleading.

This article presents the theory and workflow required to include salt deformation within basin simulators. A stress condition within the salt is developed which is used to calculate the deformation of salt in response to lateral gradients in sedimentation rate. Examples show this method applied to two dimensional regional lines in the Gulf of Mexico and new insight obtained in pressure, temperature and porosity history in the sedimentary section.

Although deep water area of Naoetsu basin is still in frontier setting in terms of oil and gas exploration, the understanding of petroleum system was deepened dramatically by the integration of various kind of knowledge.

No summary available

The objective of geological modelling is to build a realistic image of the subsurface by representing both the structural features and the lithological properties of the units. Geological model building is the basic step of basin and reservoir modelling studies. In this frame, the main input information are usually derived from seismic interpretation : e.g. horizon maps (top and base of geological units), thickness maps, facies maps… Various techniques are available to convert these information from time to depth, their accuracy strongly depends on the complexity of structural and stratigraphic variations. This paper aims at illustrating that accurate time to depth conversion of seismic results can reduce the propagation of uncertainties from geophysical to geological interpretations, limiting the ambiguities in further modelling studies. Three major pitfalls induced by inadequate time to depth conversion and giving drastic misfits in estimation of reservoir volume, connectivity network or facies distribution, are presented (geometrical issues, fault characteristics, well to surface data calibration).