From 2D Seismic to Hydrodynamic Modelling A Complex Study of Turbidites in a Petroleum-Bearing Basin Marcell Lux, HC Exploration Geologist Ahmed Amran, HC Exploration Advisor Marianna Vincze, Geomodel Development Expert MOL Plc., Exploration and Production Visegrád, 22 November 2012 Society of Petroleum Engineers 1
Outline of The Presentation Objectives Geology, lithology Depositional environment Hydrogeology, distribution of reservoir parameters Hydrodynamic conditions Hydrodynamic modelling Results, conclusions, implications Summary 2
Objectives Summarizing and assessing geology and hydrogeology and reconstructing the depositional environment to predict the distribution of reservoir properties Emphasizing seismic interpretation (2D in this case) as a key input for hydrodynamic modelling Construction of a hydrodynamic model to simulate natural flow system Assessment of the hydrodynamic system to understand HC migration driving mechanisms Data: HC wells (well log and core analyses, DSTs) 2D seismic, literature 3
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 Delta slope 4
Seismic interpretation Master seismic section Onlap reflection ending Deltaic sediments Turbidites: hummocky clinoform internal reflection pattern 5
Depositional environment Position of delta slope as a heteropic facies of turbidites Turbidites can be divided into three parts: Proximal part (T3) Sediment Distal transport part from two directions: NE and Upper (T2) NW Lower (T1) T1 is restricted to the Deltas depocenter of the NE were closer T2 is of greater extension, however it is thinning or even pinching out towards/on the flanks of the basin Sediment from the NE reached the basin depocenter earlier T3 spills over basin flanks Structure map of T2 6
Correlation of turbidite sequence GR R GR R GR R GR R GR R -1500 m Proximal turbidites (T3) Upper distal turbidites (T2) Lower distal turbidites (T1) -3500 m SW NE T1 changes in lithology towards SW (increasing silt content) and pinches out on basement highs T2 changes in lithology towards SW (decreasing sand content) and is thinner at basement highs T3 has thick sandstone pads at the NE with increasing silt content toward SW, at the NE 7 transition to delta slope can be observed
Correlation of turbidite sequence GR R GR R GR R GR R -1500 m Proximal turbidites (T3) Upper distal turbidites (T2) Lower distal turbidites (T1) NW SE -3500 m T1 has a rather constant lithology (high aleurolite content) and pinches out on basement highs T2 pinches out on the edges T1, T2 lithology is contstant -> this direction is perpendicular to sediment transport direction T3 is characterized by thinner sandstone layers at the NW 8
Depositional model Deltaic depositional system Two main directions of sediment transport T1 was deposited merely by NE deltas T2 was deposited by both deltas with the dominance of NE T3 was deposited by both deltas, however the sediments coming from different deltas differ in lithology 9
Hydrogeology, reservoir parameters Delta slope, basal marls: regional aquitards Proximal and distal turbidites: regional aquifers Porosity and permeability decreases with depth -> lower in depocenter, greater on flanks Bulk permeability map of distal turbidites 10
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 11
Hydrodynamic modeling 4 confined layers, each layer is divided into 3 sublayers 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) 12
Hydrodynamic modeling 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 13
Hydrodynamic modeling Hydraulic cross sections II. Finite difference method Finite element method 14
Hydrodynamic modeling Flow velocities, access times Acces time from bottom to top of modelled space: t = 8000-45000 years Hydraulic gradient map 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 15
Hydrodynamic modelling Hydraulic trapping Stagnation point? Hydraulic trap? Deep part of the basin: insufficient data -> high uncertainty Coincidence of different flow systems is unlikely 16 (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 17
Summary Results: 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 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 18
Thank You For Your Attention! 19
Seismic interpretation Mapping - Geometry Structure map of distal turbidites Isopach map of distal turbidites 20