The content defines geophysics and focuses on roles of seismic on exploration, well planning. It provides insights on integration of various disciplines.

1. CRASH COURSE:
Farida Ismayilova

2. FARIDA ISMAYILOVA
Total >3 years working experience as:
▪ Drilling Geohazards Specialist
Includes Geophysical interpretation
▪ PPFG Specialist
Graduate of Azerbaijan State Oil and Industry University:
▪ Bachelor’s degree in Petroleum Engineering (2017)
▪ Master’s degree in Petroleum Engineering (2019)
Don’t hesitate to ask questions during the presentation
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3. WHY IS GEOPHYSICS IMPORTANT?
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4. ▪Defining geophysics
▪Exploration geophysics
▪Well planning geophysics
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5. DEFINING GEOPHYSICS
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6. FIELD TIMELINE
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What is Geophysics?
The subsurface site characterization of the geology,
geological structure, groundwater, contamination, and
human artifacts beneath the Earth.
Major branch of the Earth sciences that applies the
principles and methods of physics to the study of the
Earth.
The non-invasive investigation of subsurface conditions in
the Earth through measuring, analyzing and interpreting
physical fields/information at the surface.
A person competent to use & understand physical
principles to study the properties of the Earth.
Who is a Geophysicist?

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Geophysics has wide applications:
within petroleum industry: logging, seismic
outside petroleum: archeology, renewable energy (example: where is it safe to place offshore wind farms?)
Geophysics crash course will focus on seismic imaging.
Well Logging Seismic Imaging Archeology

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Ultrasound scan in medicine is similar to seismic in geophysics:using sound waves for imaging.
Ultrasound imaging (sonography) is a diagnostic medical procedure that uses high-frequency sound waves to
produce dynamic visual images of organs.

9. FIELD TIMELINE
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Seismic is an image of subsurface constructed by generating (1) then recording (2) seismic waves.
Initially recorded parameters:
Amplitude (A) – how much energy was received
Two-way time (TWT) – how much time did it take the wave to travel to subsurface and reflect back to the
surface.
Then time is converted to depth and we get Amplitude vs Depth image.
1 2
Onshore seismic acquisition Seismic image

10. FIELD TIMELINE
Exploration
oil & gas
presence
Appraisal
1st
exploration
well
(wildcat)
Development
drilling more
wells
Is there
potential for
oil & gas
traps?
Where?
What is the volume?
Profitable?
Using seismic for calculating:
• oil/gas volume in the field
• formation pressure profile
of the first wells
Identifying target
boxes in the reservoir
Predicting depths of
geological horizons &
faults
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Using seismic for evaluation and calculations:
Exploration geophysics Well Planning geophysics

11. EXPLORATION GEOPHYSICS
EXPLORATION GEOPHYSICIST
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During exploration, regional large-scale seismic data are analyzed for
presence of structures, traps that can potentially hold hydrocarbons:
oil,gas, gas-condensate.
5 geological elements, known as hydrocarbon system must exist for
hydrocarbon (HC) accumulation to occur.

13. 1. Source rock – thick shale or limestone that contains
organic material: woody-plant/marine detritus (kerogen).
Organic material + Low oxygen/high pres & temp => HC
2. Reservoir rock – porous & permeable rocks like
sandstones & carbonates.
3. Migration path – conduit for HC to move from source
rock to reservoir, example: fractures, faults.
4. Trap – a geological set up that traps & fixates HC location,
examples: faults, anticlines.
5. Seal – an impermeable cap rock that will contain the
pressure and HC in the trap & prevent further migration,
example: shale.
Another important element is timing, the order in which
the elements formed.
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Oil & condensate types from Algerian field

14. For ACG field:
• Source rock – shale
• Reservoir rock – sandstone
• Trap – anticline
• Seal – shale.
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• Structural traps:
anticline
fault,
salt dome
• Stratigraphic traps:
unconformity (erosion, change/pause in sedimentation)
lens of reservoir rock
pinch out of reservoir rock
• Combination traps

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Structural traps: anticline, fault, salt dome
Gas, Oil Gas, Oil, - sealing (impermeable) fault
(1) Anticline trap
(2) Syncline
1
2
Fault trap
Spill point (SP) – after one anticline is filled with
HC until SP, it will start filling the next anticline.

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Combination trap: Anticline & Fault
Anticline

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Salt (2.2g/cc) is less dense than surrounding rocks
(example: sandstone 2.6g /cc).
That’s why it starts to behave ductile and moves up as
a dome lifting rocks around & above. It is also
acting as a seal.
Salt
dome
Seismic
image

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Unconformity
erosion,
change/pause in
sedimentation
Reefs form from
accumulation of
sediment/biotic
particles that builds
on seafloor in
relatively shallow
water (<30m).
Sand filled
channel – rivers fill
their channel beds
with particles when
flow speed drops &
abandon/change
direction.
Sand bars form
when rivers
meander/change
direction. It results in
flow speed drop &
precipitation.

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Pinch out occurs when
sediment layers become
progressively thinner to the
point of pinching out
(disappearing).
Seismic image
Geological sketch

21. FIELD TIMELINE
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Formation pressure profile defines how we will drill:
- mud weight (MW)
- casing shoe depths
Overburden pressure: vertical pressure at any point in the
earth. It’s a function of mass of rock & fluid (bulk density - ρb)
Pore Pressure : the pressure of the fluid in the pore space.
Below this pressure we might have fluid/gas kick.
Fracture Pressure : the pressure at and above which the
rock will fracture. It’s a function of pore & overburden
pressure.
In the industry formation pressure profile is called as Pore
Pressure Fracture Gradient (PPFG) plot.
The professionals who build the plot are called PPFG
Specialist.
(MW)
Shoe 1
Shoe 2

22. FIELD TIMELINE
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Overburden pressure: bulk density can be derived from
seismic data. Bulk density can vary with depths.
Pore Pressure: interval velocity data – when high
pressure, seismic waves slow down. Lithological & fluid
effects on velocity should be considered.
Fracture Pressure: is calculated from pore & overburden
pressure.
(MW)
Shoe 1
Shoe 2
Seismic data contains information about density:
AI = ρ*v
AI – acoustic/seismic impedance
ρb – bulk density
v – seismic wave velocity
Planning for exploration – no well drilled
Geophysicists provide info to PPFG specialists

23. WELL PLANNING GEOPHYSICS
PLANNING GEOPHYSICIST
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24. FIELD TIMELINE
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• Defining a target box
what is the end point of a well in productive reservoir
• Finding an optimal well trajectory
• Prediction depths of geological formations & faults,
• Avoiding risk:
• shallow gas accumulation
• mud volcanoes
Shallow gas has a small volume,not of commercial interest.Yet it poses risk for
drilling – can have high pressure,cause kicks.

25. FIELD TIMELINE
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Fields are extensive, so we need to define a
target box for a well or a cluster of wells
with:
• good reservoir properties
• profitable volume of oil & gas
Azeri-Chirag-Guneshli oil & gas field in the
Caspian basin has 430 km2 area.
Many platforms are required for such an
extent.Each platform has 48 slots to drill
wells.
Source:Wikipedia
Wellhead
Notes:
Well – drilled borehole
Trajectory – well path, planned or executed

26. FIELD TIMELINE
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Identifying a profitable target box is a decision of a
multi-disciplinary team, considering many aspects:
- Reservoir properties (permeability, oil saturation
etc.) – Petrophysicist,Geophysicist,Geologist,
Reservoir Engineer
- Geological features/structure – Geologist,
Geophysicist
- Well spacing – proper distance among producer
& water/gas injector wells – Reservoir Engineer,
Geophysicist,Geologist
target box
Trajectory
Seismic cross-section A-A’
Seismic map Logs

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Oil & gas Water

28. FIELD TIMELINE
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• Shallow gas /mud volcano
• Collision with other wells
• Wellbore instability
• Flow/Loss events
Get fruits! Avoid ghosts!
Avoid:
• Good reservoir properties
• Profitable oil/gas production
• Favorable intersection angles
• Feasible drilling window (PPFG)
Achieve:

29. FIELD TIMELINE
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Planning trajectory in 3 D
Well cluster below platforms
Avoid collision!
Trajectory in reservoir

30. FIELD TIMELINE
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Geophysicist – predicting depths of faults/horizons
Geologist, Petrophysicist – learnings, reservoir
properties from previous wells
PPFG specialist – predicting formation pressure
profile with horizon depths & previous learnings
Reservoir engineer – changing/optimizing target box
if needed
Completion engineer – analyzing feasibility of
completing the reservoir section
Drilling engineer – assessing drilling feasibility/risk of
drilling a well & adjusting trajectory if required
AN OPTIMAL
TRAJECTORY

31. FIELD TIMELINE
PREDICTION DEPTHS OF HORIZONS & FAULTS
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Geophysicist – predicting depths of
faults/horizons based on interpretations.
The random trajectory intersects Horizons 1,2,3,4
& Fault 2.
Horizon 1 – the top of the formation
Fault 2 (F2) – the fault plane
- What are the intersection depths & angles
between the trajectory & the horizons/fault?
- What is the uncertainty (error margin) of the
predictions?
Random traj.
Seismic cross-section

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HORIZONS & FAULTS IN 3 DIMENSIONS (D)
Well – drilled borehole
Trajectory – well path,planned or executed
Wells
Horizon
Seismic
section
3D horizon 1
3D horizon 2
Trajectory
Fault plane

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GAS RESPONSE ON SEISMIC
Bright seismic reflectors that are multiple times brighter than the
background can potentially be gas.

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BURIED MUD VOLCANOES ON SEISMIC
Mud volcanoes: uplift, poor imaging, gas chimney above it
Fun Facts:
• Azerbaijan has 1/3 of the world’s mud volcanoes.
• Azeri-Chirag-Guneshli field location has them too.

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SURFACE MUD VOLCANO ON SEISMIC