Reservoir Geology Using 3-D Modelling Tools
Authors: Dubrule O. , Basire C. , Bombarde S. , Samson Ph. , Segonds D. , Wonham J. 
Published: December 2007

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Abstract
Current developments in 3-D Earth Modelling have a significant impact on the practice of reservoir model construction. A structural model is first constructed on the basis of interpretations produced on a seismic workstation. Surfaces and faults are represented as geological objects, and interactively modified until considered as satisfactory. Uncertainties affecting the seismic interpretation are quantified by generating different scenarios, and calculating the sensitivity of gross-rock volume estimates to these uncertainties.
Once the structural framework has been obtained, intermediate geological surfaces not seen on seismic can be correlated between wells and constructed between the main structural surfaces. These surfaces are then used to control the construction of the three-dimensional stratigraphic grid which then guides the interpolation of reservoir properties within successive stratigraphic intervals.
Representations of reservoir properties are generated using object-based or pixel-based stochastic approaches combined with interactive modifications if the stochastic representations are not satisfactory. In some cases, deterministic modelling approaches may prove more satisfactory than stochastic ones.
Earth Modelling tools can bring various disciplines together in the same workspace, and bind them like glue. Seismic inversion or integration of fracture distribution within larger scale structural models can be also achieved much more easily if a 3-D Earth Modelling tool is used.

Introduction
3-D Reservoir Modelling Technology is now one of the fastest growing technologies in the industry, and it is recognised as strategic by petroleum companies, commercial vendors and service companies. Its growth is linked to rapid advances in computing power, visualisation technology and quantitative modelling techniques. Far from being a mere "visualisation" technology limited to the generation of pretty pictures, 3-D modelling is impacting in the very methodology of geological reservoir modelling by helping:–to store reservoir data and interpretations in the same 3-D computer model–to make all interpretations 3-D consistent–to make the sequence of operations from seismic interpretation to reservoir modelling a seamless process
First, it will be shown how the seismic interpretation can be translated into a 3-D surfacic model, within which geological surfaces not seen on seismic can be interpolated between wells. We will then describe how this surfacic model is used for the construction of sedimentary facies models. Then we will introduce the concept of a 3-D "Engine". The conclusion will stress that 3-D reservoir modelling will continue to grow at a rapid rate, significantly changing our interpretation and modelling methodologies as it does so.

Constructing a structural model
In a large majority of operational studies, structural models are derived from post-stack seismic data. The seismic interpreter, using a seismic interpretation workstation, picks seismic horizons, and the result of this horizon picking, for each horizon, is a set of data point (x,y,t) giving at each location the two-way travel time to the picked seismic horizon (Fig. 1). In most cases these interpretations are based on time-migrated horizons. The usual procedure then consists of building 2-D maps from these surfaces, and converting these maps to depth using a velocity model of varying complexity. P. 181^