In history matching and sensitivity analysis, flexibility in the structural modelling is of great importance. The ability to easily generate multiple realizations of the model will have impact both on the updating workflow in history matching and uncertainty studies based on Monte Carlo simulations. The main contribution to fault modelling by the work presented in this paper is a new algorithm for calculating a 3D displacement field applicable to a wide range of faults due to a flexible representation. This gives the possibility to apply this field to change the displacement and thereby moving horizons and fault lines. The fault is modelled by a parametric format where the fault has a reference plane defined by a centre point, dip and strike angles. The fault itself is represented as a surface defined by a function z = f (x, y), where x, y and z are coordinates local to the reference plane, with the z-axis being normal to the plane. The displacement associated with the fault outside the fault surface is described by a 3D vector field. The displacement on the fault surface can be found by identifying the intersection lines between horizons and the fault surface (fault lines), and using kriging techniques to fill in values at all points on the surface. Away from the fault surface the displacement field is defined by a monotonic decreasing function which ensures zero displacement at a specified distance from the fault. An algorithm is developed where the displacement can be increased or decreased according to user-defined parameters. This means that the whole displacement field is changed and points on horizons around the fault can be moved accordingly by applying the modified displacement field on them. The interaction between several faults influencing the same points is taken care of by truncation rules and the ordering of the faults. The method is demonstrated on a realistic synthetic case based on a real reservoir.
Three-dimensional geological modelling and reservoir simulations of an outcrop analogue to reservoirs of the Halten Terrace, offshore mid-Norway, are presented. The model of the outcrop incorporates (a) a detailed sedimentological understanding, (b) a set of stochastic realizations highly-constrained to the geological models and (c) streamline waterflood flow simulations assuming typical subsurface petrophysical properties from the Halten Terrace. Statistical analysis of simulation results has been used to show the importance of both the facies architecture and the spatial petrophysical model. The outcrop model has significantly improved the estimation of facies dimensions and architecture and gives a valuable insight into understanding petroleum reservoirs of the Halten Terrace.
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.
A stochastic approach to modeling multiple geological horizons in a layer-cake model is presented. Intercortelations between the different horizons and interval velocity fields are specified and handled properly. Bayesian statistical methods applied to Gaussian random fields provide stable and consistent predictions and simulations for all horizons and interval velocities in the model. Realistic estimates for the uncertainty can be calculated. The methodology is demonstrated by means of a instructive example as well as on a data set from a petroleum reservoir on the the Norwegian continental shelf.• Observations of the interval velocities from check-shots are can be utilized.A consequence of introducing this type of model is that 'everything is coupled to everything': By slightly changing the description of the velocities or by introducing a new observation, the prediction of every horizon and interval velocity is in principal changed. For most horizons and interval veloc-
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