structural courseoxford2

str

uctu

ral g

eolo

gy n

etw

ork

Oxford Structural Geology Seminar

Subsurface Mapping Techniques

str

uctu

ral g

eolo

gy n

etw

ork


Subsurface Structural Mapping

• Seismic interpreters spend the majority of their time making maps

• The industry maps capture a variety of data, including structural and stratigraphic features such faults, folds, unconformities, channel systems etc

• Subsurface structure maps are rarely like geological maps, but rather are topographic maps for a chosen seismic event or reflector

str

uctu

ral g

eolo

gy n

etw

ork


Basic Seismic Mapping

• Learning to Pick Wiggles!• ‘…to maximize the

geological information from the seismic data through careful structural and stratigraphic interpretation techniques, routine use of attribute and coherency mapping tools and attention to detail in the generation of structural maps…’

• Use the spatial arrangement of seismic and well data to create accurate and reliable models of the subsurface

• This is no longer done by hand, but via the use high-powered interpretative or graphic workstations that rapidly access huge volumes of 2D & 3D seismic data

str

uctu

ral g

eolo

gy n

etw

ork


Seismic Structural Interpretation

str

uctu

ral g

eolo

gy n

etw

ork


Subsurface Structure Mapping

• Structure contour maps are a common way of representing structural geometry in the energy industry

• Are often used in the past as basis for a variety of other important work

reservoir volume calculations and reservoir simulation modeling

• Starting to be superseded by true 3D models, however maps are still common communication tools between geologists, geophysicists and reservoir engineers

200

300

400

500

1100

1000

900

800

700

700

600

Fault Gap or Fault Polygon

C.I. = 50 m

1 km

N

str

uctu

ral g

eolo

gy n

etw

ork


Fault Polygon Definition

• Fault Cutoff MapsNot just gaps in horizons but the termination of discrete surfaces in space

• Geometric definitionbe as rigorous as possiblethey are not easily predictable, especially in complex structural settings Plunging folds, salt diapirs

• Requires that all structural surfaces are mapped in 3D and integrated with stratigraphic surfaces

3D Interpretation

Map Representation

str

uctu

ral g

eolo

gy n

etw

ork


The Mapping Process

• Start with the faults and think about how they connect up in 3D

• Begin infilling with the key stratigraphic surfaces

• Extend these to intersect the mapped faults

• Interpolate the surfaces over the entire area of interest

Generate grids and contour the gridded surface

• Evaluate the integrity of the resulting model

Does it make sense to you? If not, why not?

str

uctu

ral g

eolo

gy n

etw

ork



• Structure contour maps are a common way of representing structural geometry in the energy industry

• Are often used in the past as basis for a variety of other important work

reservoir volume calculations and reservoir simulation modeling

• Starting to be superseded by true 3D models, however maps are still a common communication tools between geologists, geophysicists and reservoir engineers

200

300

400

500

1100

1000

900

800

700

700

600

Fault Gap or Fault Polygon

FW Cut-off

HW Cut-offC.I. = 50 m

1 km

N

str

uctu

ral g

eolo

gy n

etw

ork



Real Normal Fault Network

Resulting 3DStructural Model

Structure Contour Map Derived from 3D Model

str

uctu

ral g

eolo

gy n

etw

ork


Using An Interpretive Workstation

• Faster, therefore cheaper• Better and more accurate,

therefore, less ‘risky’• However, demands a high degree

of geological and geophysical understanding to be more effective

• Immerse yourself in all of the data• Rapidly explore the implications

of a variety of different structural or stratigraphic interpretations

• Effectively integrate all other available subsurface data (wells)

str

uctu

ral g

eolo

gy n

etw

ork


Fault Polygon Continuity

• Zig-Zagging Polygonspossible ‘over-linkage’ of separate fault segmentsassess the interpreted length as a function of the maximum displacement on the fault surface

log length (km)-4 -2 0 2

-6

-4

-2

0

2

log

dis

pla

cem

en

t (k

m)

Con

tinuo

us F

ault

Sys

tem

Dis

cont

inuo

us F

ault

Seg

men

ts

acceptable size distribution

str

uctu

ral g

eolo

gy n

etw

ork


Coherency

• Quantitative measure of the lateral continuity of seismic events

• Actively enhances the imaging of small discontinuities such as faults, fractures, or channel margins at or close to the limit of seismic resolution

such features would be more or less impossible to map using traditional manual picking techniques

• Excellent for defining lateral extent of and linkage within fault networks

Coherency Image

str

uctu

ral g

eolo

gy n

etw

ork


3D Visualization

• ‘Slice & Dice’ the 3D seismic volume in a variety of different orientations

in-line, cross-line and time sliceshorizon and fault slices

• Co-visualization of multiple seismic attributes

multi-volume rendering and analysis

• Increasing use of auto-tracking technologies and smart ‘applets’ the recognize geological features

structural courseoxford2

Documents

reservoir

reservoir

structural

representing

true 3d models

common communication

structure

energy industry