1. Based upon work conducted by: West Texas Earth Resources Institute
Strain And Structural Partitioning In The Delaware Basin: Relation To Play And Trend Development
Dr. Richard J. Erdlac, Jr.
UTPB/CEED
Based upon work conducted by:
Douglas B. Swift
Richard J. Erdlac, Jr.
West Texas Earth Resources Institute

2. Structural Deformation Styles/Mechanisms
Exploration Premise
Determination of the play or trend type in a given region requires knowledge of:
Structural Deformation Styles/Mechanisms
You don’t say that all faults are normal when compressional tectonics were active.
Sedimentation Styles/Mechanisms
You don’t look for salt deformation structures
where salt was never deposited.

3. DEFORMATION What is meant by the term?
Structural changes that take place in the original location, orientation, shape, and volume.
Physical or chemical processes that produce the structural change.
Geologic structures that form to accommodate the changes.

4. (ORIGINAL ROCK SIZE PRESERVED) (ORIGINAL ROCK SIZE NOT PRESERVED)
1) DEFORMATION: change in original rock body.
location = translation = rigid body motion
(flexural slip folding, plate tectonics)
orientation = rotation = rigid body motion
(monocline, listric normal faulting)
(ORIGINAL ROCK SIZE PRESERVED)
shape = distortion = non-rigid body motion
(deformed fossil)
volume = dilation = non-rigid body motion
(fractures expand rock, stylolites shrink)
(ORIGINAL ROCK SIZE NOT PRESERVED)
(strain occurs)
Structural changes can vary according to scale of observations or the definition of the structural boundaries.

5. 1) Microfracturing; Cataclasis; Frictional Sliding
2) DEFORMATION : physical & chemical processes that produce structural changes (within minerals).
1) Microfracturing; Cataclasis; Frictional Sliding
(breaking of crystal lattice)
2) Mechanical Twinning; Kinking
(bending of crystal lattice)
3) Diffusion Creep (T activated)
(movement of crystal vacancies and atoms)
4) Dissolution Creep (pressure solution = stylitization)
(dissolution and reprecipitation of material)
5) Dislocation Creep
(intercrystalline slip of lattice structure along a plane)
This is usually what is meant by strain partitioning.

6. Joints and Shear Fractures Faults Folds
3) DEFORMATION : geologic structures that form to accommodate the changes.
Joints and Shear Fractures
Faults
Folds
Cleavage, Foliation, and Lineation
Shear Zones
This is what is generally considered within the exploration and production mode. However all three definitions are truly applicable.

7. What is strain partitioning?
The manner of separating different mechanisms of deformation that lead to overall bulk or average strain in a rock. (Ramsay & Huber, 1983)
(This definition tends to focus on physical and chemical changes.)
Strain can also be related to the change in any linear dimension of a body.
Strain:
(e is also called extension.)

8. Plane Strain Pure Shear = Coaxial Strain
The easiest way to consider deformation is to assume little
to no volume change in a broad sense and that one
strain axis is unchanged.
(One axis of deformation remains unchanged.)
Pure Shear = Coaxial Strain

9. Plane Strain Pure Shear = Coaxial Strain
The easiest way to consider deformation is to assume little
to no volume change in a broad sense and that one
strain axis is unchanged.
(One axis of deformation remains unchanged.)
Pure Shear = Coaxial Strain

10. Plane Strain Simple Shear = Noncoaxial Strain ( = tan)
The easiest way to consider deformation is to assume little
to no volume change in a broad sense and that one
strain axis is unchanged.
(One axis of deformation remains unchanged.)
Simple Shear = Noncoaxial Strain ( = tan)
 = 0.40
 = 0
 = 0.60
 = 1.00

11. Plane Strain Simple Shear = Noncoaxial Strain ( = tan)
The easiest way to consider deformation is to assume little
to no volume change in a broad sense and that one
strain axis is unchanged.
(One axis of deformation remains unchanged.)
Simple Shear = Noncoaxial Strain ( = tan)
 = 0.40
 = 0
 = 0.60
 = 1.00

12. STRUCTURAL PARTITIONING
Using the definitions for deformation we
can partition structures in a megascopic
manner according to the geometric styles
that predominate in a given area.
Let us look at examples within the
Delaware-Val Verde Basin region.

13. Delaware –
Val Verde
Basins
Seismic
Data

14. Delaware – Val Verde Basins
Tectonic Map
of DVVB
Play Map
of DVVB
(15)

15. STRUCTURAL PARTITIONING
T h r e e E x a m p l e s
Brown-Bassett Field: pure shear
(Brown-Bassett Play)
Waha to Coyanosa: pure shear
(Central Basin Platform Border Region)
Grisham Fault Zone: simple shear
(Grisham Uplifted Region)

16. Brown-Bassett Field
Brown-Bassett Play

17. Brown-Bassett > 1.4 B mcf
Folding/Faulting (?)
Production Map
Play Map of DVVB
JM > 705 MM mcf
Brown-Bassett > 1.4 B mcf
Will-O > 50 MM mcf
Seismic Map
Tectonic Map of DVVB

18. Folding/ Faulting (?) Brown-Bassett

19. Folding/ Faulting (?) Brown-Bassett Dry Fork Ridge Anticline, Wyoming

20. Folding/ Faulting (?) Brown-Bassett Dry Fork Ridge Anticline, Wyoming

21. Folding/Faulting (?) Brown-Bassett
Note footwall reversal. Is it real?

22. STRUCTURAL PARTITIONING
T h r e e E x a m p l e s
Brown-Bassett Field: pure shear
(Brown-Bassett Play)
Waha to Coyanosa: pure shear
(Central Basin Platform Border Region)
Grisham Fault Zone: simple shear
(Grisham Uplifted Region)

23. Waha/Worsham-Bayer-Coyanosa Area
Waha To Coyanosa
Waha/Worsham-Bayer-Coyanosa Area

24. Folding/Faulting Play Map of Seismic Map DVVB > 455 MM mcf
Production Map
Coyanosa
> 491 MM mcf E
> 989 MM mcf D
> 1 B mcf W
Waha
> 319 MM mcf E
> 241 MM mcf M
Worsham-Bayer
> 455 MM mcf
Waha, W
> 285 MM mcf
Tectonic Map of DVVB

25. DB Group Shoot 114 Folding / Faulting S Seismic Map S W W
Tectonic Map of DVVB
W,W W S
Seismic Map S W
W,W
Folding / Faulting
DB Group Shoot 114
Waha, W
Waha
Synclinal Area

26. DB Group Shoot 104 Folding / Faulting Seismic Map C C S S
Tectonic Map of DVVB C S
CBP
Seismic Map C
CBP S
Folding / Faulting
DB Group Shoot 104
Coyanosa
CBP Margin
Synclinal Axis

27. Coyanosa Anticline Axis Projection
Tectonic Map of DVVB A S
CBP
Seismic Map A S
CBP
Folding / Faulting
DB Group Shoot 105
CBP
Synclinal Axis
Anticlinal Axis
Coyanosa Anticline Axis Projection

28. DB Group Shoot 114
DB Group Shoot 105
Folding / Faulting
Fault-induced folds at outcrop scale, Devonian strata, the Appalachian Mountains (McConnell et al., 1997).
DB Group Shoot 104

29. STRUCTURAL PARTITIONING
T h r e e E x a m p l e s
Brown-Bassett Field: pure shear
(Brown-Bassett Play)
Waha to Coyanosa: pure shear
(Central Basin Platform Border Region)
Grisham Fault Zone: simple shear
(Grisham Uplifted Region)

30. Grisham Fault Zone / Grisham Uplifted Region

31. Riedel Shear Modeling Tchalenko, 1970
Simple Shear
Riedel Shear Modeling Tchalenko, 1970

32. 2o Convergent Left-Lateral System 2o Convergent Left-Lateral System
Simple Shear B 10 CM
2o Convergent Left-Lateral System 10 CM A
2o Convergent Left-Lateral System
Wilcox et al., 1973 & P.G. Temple (unpublished work)

33. Faulting/Folding/Shear Zones
Play Map of DVVB
Production Map
Greasewood > 354 MM mcf
Mi Vida > 1 B mcf
Athens > 24 MM mcf
Toyah > 7 MM mcf
Tectonic Map of DVVB

34. Faulting/Folding/Shear Zones
Seismic Map D GF A S F
Tectonic Map of DVVB
DB Group Shoot 108
Dunnavant
Grisham Fault Zone
Anticlines
Fault
Syncline
Syncline

35. Faulting/Folding/Shear Zones
Tectonic Map of DVVB A GF
Seismic Map
Seismic Map
DB Group Shoot 117
Anticline Axis
Grisham Fault Zone

36. Faulting/Folding/Shear Zones
Tectonic Map of DVVB S A
Seismic Map
Anticlines
DB Group Shoot 119B
Syncline

37. IS THE GRISHAM FAULT ZONE UNIQUE?

38. Trans-Pecos E-W Structural Zones
NB – North Baylor VH – Van Horn L – Lobo CM – Chispa Mountain ML – Mount Locke V – Valentine C – Candelaria R – Ruidosa S – Shafter (Chalk Draw Fault) P – Presidio (Tascotal Mesa Fault) T _ Terlingua (Monocline) SE – Santa Elena
Trans-Pecos E-W Structural Zones
(Dickerson, 1980 – Trans-Pecos Region – NMGS)

39. Faulting/Folding/Shear Zones

40. Other Possible Shear Zones
Toro, S
Perry Bass
Grey Ranch

41. S U M M A R Y
Deformation is documented in a variety of different ways, from microscopic to megascopic in scale physical & chemical processes – will alter porosity & permeability rigid body motion – generate permeability (fractures) & structural traps.
In its simplest manner strain can be considered to be either pure shear or simple shear (plane strain).
Deformed basins can be structurally partitioned into various strain categories (pure & simple) based upon the structural geometries or types encountered.
Knowing the partition type will define the play trend and the approach to exploration and production in that area.