Geoloy

1. Modelling of 3D Geological
Structures
By:
Zawar Muhammad Khan

2. Outline:
 What is 3D Modelling
 3D Seismic Interpretation
 Steps of 3D Modelling
 Data Required for 3D Modelling
 Basic Rules for 3D Structural Modelling
 3D Structural modeling process
 Fault Network Modelling
 Horizon modeling
 Case Study
 Conclusions
 References

3. What is 3D Modelling:
 3D modeling is the process of developing a mathematical
representation of any three-dimensional surface of object via
specialized software.
 3D modelling in geology is based on subsurface data from
boreholes, and /or seismic and geological maps. There are
different strategies of model techniques, depending on the
complexity of the regional geology.

4.  The basic and first step required for 3D modelling is 3D
seismic Interpretation.

5. PICKING THE FIRST INLINE

6. PICKING THE FIRST CROSSLINE

7. INLINES & CROSSLINES PICKED FOR ALL WELLS

8. TIME SLICE PICKS ADDED

9.  3D subsurface modeling is used for:
 (1) improving data interpretation through visualization and
confrontation of data with each other and with the model
being created.
 (2) generating a support for numerical simulations of
complex phenomena in which structures play an important
role.

10. Steps of 3D Modelling:
 A: Data georeferencing.
 B: Picking of relevant structural objects.
 C: Creation of fault network.
 D: Horizon modeling.

11. Data georeferencing.

12. Picking of relevant structural objects. (Curves with spherical nodes
denote faults; curves with cubic nodes denote stratigraphic contacts)

13. Creation of fault network

14. Horizon modeling

15. Data Required:
 The typical input data for a 3D structural modeling project can
be quite diverse and may include
 1. Field observations(for instance stratigraphic contacts and
orientations, fault planes).
 2. Interpretive maps and cross-sections.
 3. Remote sensing pictures.
 4. Reflection seismic.
 5. Borehole data.

16. Basic Rules for Structural Modelling:
 The surface orientation rule states that a geological surface is
always orient-able.
 Surface non-intersection rule states that any two surfaces should
not cross each other, except if one has been cut by the other.
 Surfaces (Horizons and Faults) should fit the data within an
acceptable range depending on data precision and resolution.
 Well data should generally be honored much more accurately.
 Relationships between the geological interfaces should be correct.

17.  Structural modeling is generally achieved in two steps:
 1. Fault surfaces are first built to partition the domain of study into fault
blocks.
 2. Stratigraphic horizons are created.
Structural modeling process:

18. Fault Network Modelling:
 Faults are very important in structural modeling, for they partition space
into regions where stratigraphic surfaces are continuous.
 Therefore, it is important to generate faults and to determine how faults
terminate onto each other before considering other geological surfaces.
 Defining the connectivity between these fault surfaces is probably the
most important and the most consequential step in structural modeling.
 This can usually be done by considering the geometry of both fault data
and surrounding horizon data to assess the fault slip.

19.  Indeed, the fault slip should always be null at the fault boundary,
therefore, when a horizon on either side of a fault is significantly offset
near the fault boundary.
 This suggests that the fault should be extrapolated or projected terminates
onto another fault.
 This information can then be used to fill the gap between the branching
fault and the main fault.

20. Horizon modeling
 Horizon construction may be achieved fault block by fault block, from
horizon data.
 The logical borders must then be defined interactively to ensure that
horizon borders are properly located onto fault surfaces.
 This block-wise approach is adapted for simple models with few faults.
 Each step of the process is manually controlled, and can be specifically
adjusted to the goal at hand.

21. Case Study
THE DEVELOPMENT OF A 3D STRUCTURAL-GEOLOGICAL MODEL
AS PART OF THE GEOTHERMAL EXPLORATION STRATEGY – A
CASE STUDY FROM THE BRADY’S GEOTHERMAL SYSTEM,
NEVADA, USA
Egbert Jolie, James Faulds, Inga Moeck

22.  The focus for the Brady’s geothermal system located in the Basin and
Range province is on the identification of structural controls on fluid flow
and permeability anisotropy.
 The data used as input parameters of the 3D model is
 1) detailed geological maps,
 2) borehole data,
 3) processed 2D seismic and gravity data,
 4) a digital elevation model
 Based on these data, four representative cross sections have been
developed as a major input for a preliminary 3D geological model.

23. Development of Cross Section
Study area with fault traces (red), well locations, and developed cross sections
(B, C, D, E).

24. Process of data preparation for the development of a 3D structural model.
The entire model is based on four geological cross sections and a geological
map.

25. Fault modeling
Final fault model with 61 fault planes. The dominant strike direction of the fault
system is NNE (~N30E).

26. Horizon modeling
Horizon model of the Brady’s geothermal system. The top horizon represents the
early to late Miocene.

27. Results
3D geological model with the proposed stimulation well 15-12.

28.  The 3D structural-geological model of the Brady’s geothermal
system comprises of:
61 fault planes.
Eight geological units.
71 large fault blocks.
The dip angles of the faults vary from 45° to 80°.
The major strike direction is NNE.
The known geothermal reservoir is located at a depth of 600-1,500
m below surface.
Production wells target the NNE-striking Brady’s fault, which has a
dip range from 70°-80°.
Compartmentalization due to faults has effects on the hydraulic
conductivity, as it can isolate or connect production wells from
each other.

29. Conclusions:
 3d geology models are the future oriented base for subsequent
hydrogeological and environmental modelling, as well as for geotechnical
and GIS based spatial planning.
 3D models can be used as a consistent data base as well as structural
model for subsequent modelling of groundwater flow and transport.
 Understanding the spatial organization of subsurface structures is essential
for quantitative modeling of geological processes.
 The quality and reliability of available data should be considered to define
the data integration strategy.
 Although the direct generation of compatible geological structures often
remains a problem, visual quality control is a must to detect
inconsistencies.

30. References:
 Chilès JP, Aug C, Guillen A, Lees T (2004). Modelling the geometry of
geological units and its uncertainty in 3D from structural data: the
potential-field method. In: Dimitrakopoulos R, Ramazan S (Eds.) Orebody
modelling and strategic mine planning, Perth, WA: 313–320.
 Culshaw MG. (2005) From concept towards reality: developing the
attributed 3D geological model of the shallow subsurface. Q J Eng Geol
Hydrogeol 38(3):231–384