# Exercises

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Exercise A1-1: Interpreting folds in poorly imaged zones
Interpret the poorly imaged zone on this structure as a steep fold limb using the method described on the previous page. Does the predicted fold limb properly "connect" seismic horizons on each side of the poorly imaged zone?

Part A1: Folds

Seismic Exercise: Permian basin, Texas, USA

Solution Instructions
Step 1: Jump correlatereflections across the poorly imaged zone. Step 2: Pinpoint truncations of reflections as they enter the poorly imaged zone. Step 2: Pinpoint truncations of reflections as they enter the poorly imaged zone. Step 4: Define the dip of beds in the kink band by making γ2 equal to γ1.

γ=61°

5 km

58°

Step 5: Compare interpolated horizons with your initial jump correlation. What can be done toimprove the match?

7

Post-stack time migration displayed in depth (V.E. = 1:1).

Data courtesy of Texaco, Inc.

Exercise A2-1: Interpreting thrust ramps on seismic sections

Part A2: Faults

Interpret the thrust ramps using the three fault recognition criteria. S e is mic Exe rc is e : Pe ruvian Ande s

2
1

dipping over horizontal reflections

1

1 1

3

dipping overhorizontal reflections

2
3
1
VE of 1:1.
fro m S ha w e t a l., 1998; Da ta co urte s y o f PERUPETRO.

inte rpre te d fa ults
VE is 1:1.

5 km

This section images structures that involve two large thrust faults, which can be interpreted using the fault recognition criteria. The section is interpreted using: Cutoffs (1), kink band terminations (2), and fault-plane reflections (3).Note how a series of cutoffs and kink-band terminations can corroborate, and be used to extrapolate beyond, the fault-plane reflections. (2D seismic data, reprinted from S haw et al., 1998, and published courtesy of Perupetro).

S olution

Exercise A2-2: Interpreting detachment levels

Part A2: Faults

Interpret the prominent detachment and associated thrust ramps using the faultrecognition criteria.

S e is mic Exe rc is e : S ic huan bas in, China
back thrust

1 km

E
0

we dge
upper detachment wedge tip

forethrust

5km

fro m S ha w e t a l., 1995, Da ta c o urte s y o f CNPC

Exercise B1-1: Synclinal fault-bend fold
Interpret the synclinal fault-bend fold using the graphs provided on the previous pages. θ and γ can be readily determined from the seismicimage, and used to calculate φ and β.

Part B1: Fault-bend folds

Seismic Exercise: Argentina

0.5 km
2

3

θ = 15º γ = 82º φ = 15º

γ γ = 82°
β = 14° θ = 15° φ = 15°

β = 14º 4

Data courtesy of BHP

5km

Exercise B1-2: Anticlinal fault-bend fold
Interpret the anticlinal fault-bend fold using the graphs provided on the previous pages. θ and γ can be readily determined fromthe seismic image, and used to calculate φ and β. Seismic Exercise: Niger Delta

Part B1: Fault-bend folds

0.5 km

2

β = 28°

S1

γ = 80° θ = 24°

θ = 24º 3 γ = 80º φ = 16º

φ = 16°

S0
4

β = 28º

Data courtesy of VERITAS

Exercise B1-3: Composite fault-bend fold
Complete the structural interpretation using fault-bend fold theory. Does the fault sole to a basaldetachment?

Part B1: Fault-bend folds

Seismic Exercise: Permian basin

1 km
2

Instructions Step 1: Interpret the upper detachment and forelimb axial surfaces. Step 2: Measure the forelimb cut-off (β) and the forelimb interlimb angle (γ). Step 3: Use the anticlinal fault-bend folding graph to determine the dip of the ramp (based on φ) and the initial cut-off angle (θ). Determine R. 3 Step 4:Interpret backlimb axial surfaces (note: use slip on upper detachment and R value to define backlimb width). Step 5: Measure the backlimb cut-off (β) and interlimb angle (γ). Step 6: Use the synclinal fault-bend folding graph to determine the change in dip of the ramp (φ) and the initial cut-off angle (θ). Step 7: Interpret the geometry of a few key horizons based on your fault-bend fold...