From 2D Seismic to Hydrodynamic Modelling A Complex Study of Turbidites in a Petroleum-Bearing Basin Marcell Lux, hydrogeologist engineer Tamás György Krusoczki, hydrogeologist engineer MOL Plc., Eurasian Exploration & Production ISZA, Tatabánya, 31 March 2012

Outline of The Presentation Objectives Geology Hydrogeology Hydrodynamic conditions Hydrodynamic modelling Results, conclusions, implications Summary

Objectives Summarizing and assessing geology and hydrogeology Construction of a hydrodynamic model to simulate natural flow system Finite difference method (Processing Modflow 7) Finite element method (FEFLOW 6.0) Assessment of the hydrodynamic system Data: HC wells (well log and core analyses, DSTs) 2D seismic, literature Comparison

Geology Neogene sub-basin Surroundings uplift during basin subsidence Deltaic depositional system Assessed late-miocene formations: Basal marls Pro-delta turbidites Distal (main emphasis, possible tight gas reservoir) Proximal (several conventional HC accumulations) Delta slope

Seismic interpretation – Master seismic section Onlap reflection ending Deltaic sediments Distal turbidites: hummocky clinoform internal reflection pattern TWT

Seismic interpretation – Mapping Structure map of distal turbidites top Isopach map of distal turbidites

Hydrogeology Delta slope, basal marls: regional aquitards Proximal and distal turbidites: regional aquifers Porosity and permeability decreases with depth -> lower in depocenter, greater on flanks Permeability map of distal turbidites

Hydrodynamic conditions A moderately super-hydrostatic zone is followed by a strongly overpressured regime Transition within proximal turbidites, distal part is highly overpressured Flow is mainly directed upward Faults play an important role in the dissipation of overpressures Fluid potential map of basal marls

Model grid of the finite element method (Vogt, 1993) Hydrodynamic modelling 4 confined layers, each layer is divided into 3 sub- layers to enhance vertical resolution Geometry from well data and seismic interpretation Effective porosity and hydraulic conductivity from parameter distribution maps Ratio of vertical and horizontal hydraulic conductivity determined from available core analyses Hydraulic head data from DSTs Fixed head cells at top and bottom Steady-state flow -> Permanent model Finite difference method and finite element method Model grid of the finite difference method (Chiang and Kinzelbach, 1999) Model grid of the finite element method (Vogt, 1993)

Hydrodynamic modelling – Hydraulic cross sections I. Flow is directed upward Horizontal component toward deep grabens Potentiometric „mounds” above basement highs Finite element method: congestion of equipot. lines Finite difference method Finite element method

Hydrodynamic modelling – Hydraulic cross sections II. Finite difference method Finite element method

Hydrodynamic modelling – Flow velocities, access times Hydraulic gradient map Acces time from bottom to top of modelled space: t = 8000-45000 years Average vertical flow velocities: (1÷6) ×10-9 m/s Average hydraulic gradients: I = 0,8-3 Extremely high hydraulic gradients, still low flow velocities -> very low permeability! Acces times

Hydrodynamic modelling – Hydraulic trapping Stagnation point? Hydraulic trap? Deep part of the basin: insufficient data -> high uncertainty Coincidence of different flow systems is unlikely (Fetter, 1994)

Hydrodynamic modelling – Overpressure prediction Hydraulic head (pressure) values correspond to every single point of the modelled space 1000 m equipotential surface is approx. 100 bar (10 MPa) overpressure

Summary Results: Improvements may include: Geological overview of the basin, more detailed investigation of distal turbidites Systematic hydrogeological description of the basin’s deeper formations Characterizing the hydrodynamic system based on a hydrodynamic simulation Fluid potential maps Hydraulic cross sections Access times Flow velocities Identification of a possible stagnation point No significant discrepancy between finite difference and finite element method Improvements may include: Using seismic attributes to refine geological and hydrogeological model More detailed structural geological investigations Advantages of finite element method can be utilized better High-resolution quantitative well log analysis

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