Basin Geology 8 May

STRUCTURAL GEOLOGY

Gianfranco Fontanesi

San Donato Milanese

8 May 2007

STRUCTURAL GEOLOGY 1) Structural Modelling: a) Identification of the Structural Styles b) Reconstruction of the tectonic phases and timing of the deformation c) Construction and restoration of geologic crosssections d) 3D Restoration

2)

Fault Seal Analysis: a) Input Data b) Fault Juxtaposition c) Shale Gouge Ratio

STRUCTURAL GEOLOGY: Introduction

Structural Modelling

Petroleum System Modelling

Structural Geology

Fault Seal Analysis

2D/3D Geologic Model

Dynamic Modelling Fault & Fracture Analysis

STRUCTURAL MODELLING

STRUCTURAL GEOLOGY: Structural Modelling Recognition of the Structural Styles and Geometries: *

Provide a basic structural and geometric framework to help the seismic interpretation * QC of the interpreted structural (faults and horizons) features and building of the geometric model * Build of geologic model through the integration of the geometric model with all the available geologic informations

2D Restoration and Balancing:

Structural Modelling

* Validate the interpreted structural and geologic features * Definition of the main deformation phases * Definition of the timing of the deformation

3D Restoration: * *

Definition of the timing of the deformation

Creation of restored structural maps as direct input for Petroleum System Modelling (migration path analysis) * Definition of the timing of the trapping mechanisms related to the main naftogenic process (expulsion and migration) as direct input for Petroleum System Modelling

STRUCTURAL GEOLOGY: Structural Modelling Analogue models..

represent a possible guidance in complex geology areas

STRUCTURAL GEOLOGY: Structural Modelling and coupled with the geologic knowledge of an area

provide the basic information for building a structural framework….

STRUCTURAL GEOLOGY: Structural Modelling

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that can help the 2D and 3D seismic interpretation..

STRUCTURAL GEOLOGY: Structural Modelling

WELL STRIKE-SLIP FAULT

and finally the creation of a geometric and..

WELL

of a geologic model

STRUCTURAL GEOLOGY: Structural Modelling Reconstruction of structural evolution using 2D restoration tools Main detachment plane

Present time geologic profile Splitted modules along detachment plane

STRUCTURAL GEOLOGY: Structural Modelling Reconstruction of structural evolution using 2D restoration tools

Restoration above detachment Reconstruction of missing portions

Restoration below detachment

2D Sequential restoration

Restored profile

STRUCTURAL GEOLOGY: Structural Modelling

Reconstruction of structural evolution using 2D restoration tools Depth converted seismic interpretation 400 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000 10500 11000 11500 12000

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SPBI98R-106

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Modules restoration

E 2050m

Present day geologic model

Sequential backstripping

Restored profile

STRUCTURAL GEOLOGY: Structural Modelling

Seismic interpretation - Depth domain

Present day geologic model

Sequential backstripping and restoration

STRUCTURAL GEOLOGY: Structural Modelling

3D Restoration

Paleo-structural map of top reservoir layer at selected time obtained by reconstruction through 3D restoration Present Time

3 MY

4.8 MY

10.1MY

STRUCTURAL GEOLOGY: Structural Modelling 3D Restoration provides information about structural evolution Structure not present yet Structure delineated

? 10.1 M.Y., no HC expulsion

Structure already present with possible extensions

? ?

Strucure likely filled of HC 4.8 M.Y., beginning of HC expulsion

?? 3 M.Y. Peak of HC expulsion

Top reservoir at present day

Fault Seal Analysis

STRUCTURAL GEOLOGY: Fault Seal Analysis

Faults can be considered (irrespective of the presence or not of movement along the fault plane) as interruptions in the physical continuity of a rock. If the rock is a reservoir faults can play an important role in fluid flows. Two basic types of fault flow models: Faults in siliciclastic reservoirs: detrimental to fluid flow

A

Faults in fractured reservoirs: propitious to fluid flow

Fault Seal Analysis deals with the proofing effectiveness of faults in presence of hydrocarbons and to test the capability of such faults in constituting an effective closure for a hydrocarbon trap. As such Fault Seal Analysis is applied for faults affecting siliciclastic reservoirs Structure A has two sides closing against faults

STRUCTURAL GEOLOGY: Fault Seal Analysis But what happens to the rocks on both sides of the fault when we have movements along the plane?

Heave la Disp

Normal fault Zones Painted Canyon, California

ce m e nt

T h r o w

FOOTWALL HANGINGWALL

Rocks are displaced Rocks are fractured

STRUCTURAL GEOLOGY: Fault Seal Analysis Two basic types of fault seal:

Im

rou Po

rm pe

ea

bl e

s

Juxtaposition Seal

Membrane Seal

Geometric Properties of the Fault Plane

Petrophysic Properties of the Fault Rock

The properties of the fault plane can change……..

STRUCTURAL GEOLOGY: Fault Seal Analysis

Sandstone-1

Along the dip of the fault plane or…… Sandstone-2

2.1 m displac. Normal fault Zones, Round O Quarry, Lancashire, UK (From Childs et al. (1998)

3m displac. Normal fault Zone (15m displ.) Round O Quarry, Lancashire, UK (From Childs et al. (1998)

STRUCTURAL GEOLOGY: Fault Seal Analysis

Along the strike of the fault plane

Round O Quarry, Lancashire, UK (Childs et al., 1996)

Moab Fault, SE Utah (Foxford et al., 1998)

STRUCTURAL GEOLOGY: Fault Seal Analysis Juxtaposition Sealing Modelled Fault

Throw Analysis

Allan Maps

Footwall Hangingwall

STRUCTURAL GEOLOGY: Fault Seal Analysis Juxtaposition Sealing

Sand on sand Shale on Shale

The juxtaposition of Sand against Shale or Shale against Shale does not represent a problem because in these intervals the fault is considered sealing. It is more complicated when we have juxtaposition, across the fault plane of Sand against Sand as in this case we are dealing with a case of MEMBRANE SEALING

STRUCTURAL GEOLOGY: Fault Seal Analysis Membrane Sealing Pe

The primary control on the seal behaviour of faults under static pressure conditions is likely to be the clay/shale content of the fault zone.

Theory: Hydrocarbon Column Height (Z) must exceed Pe (Entry or Capillary Pressure for leackage to occur.

Z=Pe/[(ρw-ρo)g]

STRUCTURAL GEOLOGY: Fault Seal Analysis Membrane Sealing: Fault Rock Properties

Petrophysical properties of the fault rock depend from a number of different factors among which: •lithology of the host rocks •cataclasis •shale smear/gouge •cementation

STRUCTURAL GEOLOGY: Fault Seal Analysis Membrane Sealing Fault Rock Capillary Threshold Pressure

STRUCTURAL GEOLOGY: Fault Seal Analysis Membrane Sealing

Several algorithms have been developed to assess the clay/shale content of the fault zone. Some of them such the CSP (Clay Smear Potential, Bouvier et al., 1989) are qualitative assessment while the most used is the SHALE GOUGE RATIO (SGR, Yielding et al., 1997)) which can considered as the percentage of shale or clay in the slipped interval and is a function of the shale/clay volume (Vshale) of the host rocks.

STRUCTURAL GEOLOGY: Fault Seal Analysis Membrane Sealing

Visualization of Vshale on the fault plane. The shale layers can be easily detected

The shale volume of a rock is expressed by the Vshale Curve that is calculated through the integration of various “lithologic” logs such as Gamma Ray, Density, etc. This curve shows values comprised between 0 (sand) and 1 (shale).

STRUCTURAL GEOLOGY: Fault Seal Analysis Membrane Sealing

The SEALING POTENTIAL of a fault is defined through the calculation of SGR for each potential fault throw. The juxtaposition diagram illustrates the range of the calculated SGRs for all these potential throws.

STRUCTURAL GEOLOGY: Fault Seal Analysis Membrane Sealing

Visualization of the SGR on the Fault Plane

SGR>35% Fault is sealing 15%<SGR>30-35%

Fault is probably sealing

SGR<15% Fault is leaking

STRUCTURAL GEOLOGY: Fault Seal Analysis Membrane Sealing If SGR fall in this range, seal attributes must be calibrated with in-situ pressure data to derive a measure of the “strenght” of the seal and hence the hydrocarbon column height. Ideally SGR values should be calibrated against the difference in pressure between the hydrocarbons trapped at the fault and water in the fault zone. This difference has been called Across-Fault-PressureDifference (AFPD) by Bretan et al. (2003) and coincide with the Capillary Pressure (Pc) However, as it is generally not possible to collect accurate pressure data for water in a fault zone, the difference in pressure can be obtained either by measuring the pressure difference between the hydrocarbon and water phases in the same reservoir or by measuring the difference in pressure across the fault. If there is a common aquifer the Capillary Pressure coincides with the Buoyancy Pressure However we must take into account that sometimes the aquifer across the fault it is not the same and that sometimes we juxtaposition of different type of fluids. The basic types are: hydrocarbons (oil or gas) against water hydrocarbons against hydorcarbons water against water

STRUCTURAL GEOLOGY: Fault Seal Analysis Membrane Sealing To sum up in order to calibrate SGR values against pressure data we need the following information: PRESSURE DATA

Oil pressure gradient OWC

Water pressure gradient

For each layer

considered

STRUCTURAL GEOLOGY: Fault Seal Analysis Membrane Sealing FLUID JUXTAPOSITION

Oil-Water contact Water Oil On hanginwall footwall

and

STRUCTURAL GEOLOGY: Fault Seal Analysis Membrane Sealing FLUID PRESSURE

On the block

same

fault

STRUCTURAL GEOLOGY: Fault Seal Analysis Membrane Sealing DIFFERENCE IN FLUID PRESSURE

Between Footwall and Hangingwall

STRUCTURAL GEOLOGY: Fault Seal Analysis Membrane Sealing

Calibration plot of SGR against across-faultpressure-differences (AFPD, Bretan et al., 2003) have been collected from a variety of fault data sets worldwide (Yielding, 2002) and for different burial depth. From this plot derives that there is a linear relationship between SGR and AFPD and that can be written as: AFPD(bar)=10(SGR/27-C) Where: C=0.5 for depth less than 3.0 km C=0.25 for depth between 3 and 3.5 km C=0 for depth exceeding 3.5 km

STRUCTURAL GEOLOGY: Fault Seal Analysis Membrane Sealing

The empirical relationship between AFPD (Pc) and SGR can then be used to derive the Potential Hydrocarbon Column Height that each part of the fault may be able to support: H=AFPD(Pc)/g(ρw-ρo) Where: g=gravity acceleration ρw=pore-water density ρo=hydrocarbon density

STRUCTURAL GEOLOGY: Fault Seal Analysis Membrane Sealing

Fault Seal analysis can be used in explorative studies to define the maximum column eight sustained by a fault bounded prospect: H=AFPD(Pc)/g(ρw-ρo)

A