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

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.

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.

(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.

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.

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.

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.)

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

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

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

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

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.

Delaware – Val Verde Basins Seismic Data

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

Brown-Bassett Field Brown-Bassett Play

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

Folding/ Faulting (?) Brown-Bassett

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

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

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

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)

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

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

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

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

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

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

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)

Grisham Fault Zone / Grisham Uplifted Region

Riedel Shear Modeling Tchalenko, 1970 Simple Shear Riedel Shear Modeling Tchalenko, 1970

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)

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

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

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

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

IS THE GRISHAM FAULT ZONE UNIQUE?

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)

Faulting/Folding/Shear Zones

Other Possible Shear Zones Toro, S Perry Bass Grey Ranch

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.