EARS5136slide 1 Theme 6: INTEGRATION OF STRUCTURAL DATA AND RESERVOIR MODELS

EARS5136slide 2 Basis of fault modeling in reservoir simulations Reservoir models of entire field (‘full-field’) or part of a field (‘sector’) Faults considered as single plane Modelled flow path as part of cross-cell flow calculation Use modifiers of transmissibility between cells

EARS5136slide 3 Manzocchi et al. (2002)

EARS5136slide 4 Fault zone transmissibility Fault Rock Thickness Fault Rock Permeability Transmissibility (Perm x Fault rock thickness) Hydraulic Resistance (Fault rock thickness / Perm) Matrix Properties Cell Size

EARS5136slide 5 Only Cross-fault cells used : - No along fault flow considered. - No Threshold Capillary Pressure considered. Separate cells for faults allows along fault flow evaluation. Transmissibility multipliers and flow modeling

EARS5136slide 6 Fault zone hydraulic resistance Flow across a fault in reservoir models follows Darcy flow: The rate for linear flow is: q = (k/ L) (A/  ) (  1 -  2 ) For a given cross-sectional area, A, across the fault and a constant pressure gradient and fluid viscosity, the flow rate is dependent on the fault zone hydraulic resistance or, (k/L), where L is the fault rock thickness.

EARS5136slide 7 Transmissibility – no fault Fault zone properties are introduced into reservoir models as transmissibility multipliers. Average permeability for flow between adjoining cells with no fault is: k undeformed = L / [(0.5L 1 / k 1 ) + (0.5L 2 / k 2 )] And transmissibility (T trans ) is K undeformed /L No fault reservoir cell 1 reservoir cell 2 L L1L1 L2L2 k1k1 k2k2

EARS5136slide 8 Fault transmissibility – with fault Average permeability for flow between adjoining cells with a fault is: k faulted = L / [0.5 (L 1 - L f ) / k 1 ] + [0.5 (L 2 - L f ) / k 2 ] + [L f / k f ] With fault reservoir cell 1 reservoir cell 2 fault L L1L1 L2L2 k1k1 k2k2 LfLf

EARS5136slide 9 Transmissibility multiplier - T Transmissibility with a fault is altered by transmissibility multiplier, T T trans = T (k undeformed /L) for no fault T=1 and for a completely sealing fault T=0 The transmissibility multiplier is the ratio of the faulted permeability to the undeformed permeability that is: T = k faulted /k undeformed This is the key relationship introduced into reservoir models.

EARS5136slide 10 Transmissibility multiplier - T The transmissibility multiplier is: T = k faulted /k undeformed where, k faulted = L / [0.5 (L 1 - L f ) / k 1 ] + [0.5 (L 2 - L f ) / k 2 ] + [L f / k f ] is a function of the fault permeability, k f and fault rock thickness, L f. The fault rock thickness is associated with the fault throw, L f.

EARS5136slide 11 Fault rock thickness Fault rock thickness scales with fault displacement

EARS5136slide 12 Manzocchi et al. (2002)

EARS5136slide 13 Fault rock permeability vs. clay content

EARS5136slide 14 Fault Zone Flow Transmissibility depends on cell size

EARS5136slide 15 Fault Zone Flow Transmissibility depends on cell size

EARS5136slide 16 Fault Rock Prediction: Heidrun field Knai & Knipe (1998)

EARS5136slide 17 Fault rock thickness Geocellular models for reservoir modeling

EARS5136slide 18 Fault rock permeability Geocellular reservoir models Geologists provide reservoir engineers input along faults for modeling.

EARS5136slide 19 Base Hydrocarbon Sealing Capacity Threshold Pressures and Flow Modeling Constant Fault Rock Properties P < Pth Fault seals No Flow. Permeability based Transmissibility not applicable, Water filled fault. P > Pth Fault leaks

EARS5136slide 20 Fault zone flow effectiveness Fault zone complexity cannot be explicitly modelled in current reservoir simulators. Capture essential details by determining effective fault rock thickness. Minimise fault rock thickness on all pathways - assumed to be most efficient flow path.

EARS5136slide 21 5cm Cumulative fault rock thickness Cataclastic faults in porous sandstones build up cumulative fault rock thickness

EARS5136slide 22 Fault Populations Fault Connectivity Fault Rock Permeability Fault Rock Distribution Matrix Flow Modified Matrix Tortuosity Factor Fault Rock Flow 0 100% COMPONENTS: Fault Transmissibility Assessment

EARS5136slide Define number of faults crossed along critical flow paths through fault zones % by-passed ? 2. Define total thickness of fault rocks present along the critical flow path 3. Define permeabilities and threshold pressures of the different fault rocks along pathways 4. Calculate the effective transmissibilities, and threshold pressures of fault zones Fault transmissibility evaluation: workflow

EARS5136slide 24 Complex fault modelling Study impact of 3D spatially distributed faults on flow properties of complex fault zones. Analyse tortuosity and connectivity in terms of fault zone geometry. Analyse spatial clustering techniques (core, outcrop & seismic scale). Model influences of host rock and fault rock permeability ratio. Results accessible to reservoir simulation packages - fault rock thickness, transmissibility multipliers.

EARS5136slide 25 Model attributes Position, length, width, strike, dip, aspect ratio Clustering technique – hierarchical Throw:thickness and throw:length ratios BASIC ASSUMPTIONS: Fault lengths are members of power law size-frequency distribution Faults elliptical and planar; orientation unrestricted Damage zone of clustered faults around major faults

EARS5136slide 26 A Two-Dimensional Illustration

EARS5136slide 27 Collapsed Fault Rock Thickness Hierarchical Clustering Technique Strike view of fault zone

EARS5136slide 28 Fault Spacing Along 1D Traverse Two-Dimensional Horizontal Slices Hierarchical Clustering Technique

EARS5136slide 29 Modelled Volume of Interest

EARS5136slide 30 Controls on Pathway Length and Fault Rock Thickness Direct Path (low frequency): Low connectivity of fault array, low fault rock thickness. Tortuous Path (medium frequency): Increased connectivity, long pathways, low fault rock thickness. Direct Path (higher frequency): Effective barriers, low tortuosity pathways, significant increase in fault rock thickness.

EARS5136slide 31 High K h /K f K h ~ K f Impact of permeability ratio of host rock and fault rock Permeability ratio controls host rock pathway lengths which can be traversed before faults are crossed. Modelled by adding a “background” value to each cell in addition to fault rock thickness values.

EARS5136slide 32 Transmissibility Multiplier Permeability ratio  3334