The importance of geohazards for safety, rig/well integrity & drilling. It includes real incidents & worst case scenarios. Pressure concepts, seismic and diagrams are utilized to explain given examples.

1. Drilling
geohazards in
oil & gas industry
Farida Ismayilova

2. About myself
Farida Ismayilova
Total >3 years working experience as:
• Drilling Geohazards Specialist
• PPFG Specialist
Graduate of Azerbaijan State Oil and Industry University
Master’s & Bachelor’s degree in Petroleum Engineering
Notes:
Questions during the presentation
Examples analogical to Caspian basin (confidentiality)

3. Agenda
Geohazards:
✓Definition
✓Importance
✓Types
Drilling Geohazards Specialist:
✓Skill requirements
✓Responsibilities

4. Industry Geohazard Definition
• A geological condition that has the potential to cause harm to man or damage
to property.
• Geohazards can be relatively small features, but they can also attain huge
dimensions.
Examples:
• Shallow gas/water flow
• Mud volcanoes
• Land slides
• Soils reactivity & etc.
Geohazards??

5. So why Marine Geohazards?
Operational Safety, Environment and Integrity
Safety: Operational Safety
Environment: Leave the environment as found
Integrity: Long term safe working of facility
Compliance:
Regulatory
Operator Internal Policy
Operational Efficiency
Delivering a well or project on schedule and on budget

6. Norway: 1985 Shallow Gas Blowout

7. Seabed Complexity: Slope Stability
Discovery and Appraisal
Well Locations
Storegga Slide, mid-Norway

8. Australia, 1996 Jack-up leg punch through
• November 1996, jack-up rig “punch through” a hard layer of sediment
approximately 10m below the seafloor during preload.
• The rig sustained considerable damage to its three legs and had to be
severed from each leg prior to recovery of the rig.
• The legs were subsequently recovered independently.

9. Drilling Geohazards Specialist (DGS)

10. Objective of Drilling Geohazards Specialist (DGS)
DGS is a person who integrated knowledge and data of different
disciplines to ensure safe, smooth drilling & operations.
In the Caspian region DGS is responsible for ~1000m below sea surface

11. Skills for a Drilling Geohazards Specialist
• Geology:
− Understanding formation properties
− Interpreting geological structures & formations
• Geophysics:
− Interpretation on seismic
− Basic understanding of logs interpretation
• Pore Pressure Fracture Gradient (PPFG):
− Understanding optimal design & MW based on PPFG
− Pressure understanding in case of integrity issues
• Drilling:
− Analyzing drilling data if required
− Recommendations on M

12. Geohazards: requires skills integration
• Main sources of information: seismic, experience & data
acquired during drilling
• Successful Marine Geohazards studies require the
participation of numerous skills families:
− Geoscientists: to identify the potential sources of geohazard risk
present and to clearly communicate this.
− Engineers: to receive this information and to take appropriate
engineering steps to mitigate the risks identified.
− Both Disciplines: to capture learnings to ensure mistakes are not
repeated and allow continuous improvement – over life of field.

13. Role of Geohazards in Field Life Cycle
Access
Development
Appraisal
Production Abandon
Exploration
Available data, experience increase resulting smoother delivery and optimal well design
E & A stages:
Where is it safe to:
- Put drilling rig/platform
- Drill 1st wells
D & P stages:
How to drill formations:
- Without major issues
- Efficiently & fast
Contributing to well
& platform integrity

14. Life of Field Needs
• Development of understanding over life of operations requires:
• Capture and communication of interpretational and operational
learnings over time
• Continual focus on the fitness of geophysical imagery
• Correct data to support the operation being addressed and
renewal over time
• Consider risk of a dynamic overburden, effects of:
• Subsidence, fault re-activation, sealed zones penetrated,
waste injection integrity, pressures etc.
• Integration of broad range of required skills and new technologies
• Geoscience
• Wells and Facility Engineering

15. Geohazards

16. Winner in Marine
Geohazards risk?
Mexico (Campeche)
Canada
(Newfoundland)
Canada (Beaufort)
UK (CNS)
Uruguay
Norway (Mid)
Angola (DW)
Mauritania (DW)
Azerbaijan
Brasil
Australia
(Deep Water)
Trinidad (Shelf)
Indonesia (Birau)
US (DW GoM)
Senegal (DW)
?

17. Azerbaijan 25+ years on:
Ongoing World Champion in Marine Geohazards
Benthic
Communities
Hydrates
Shallow water flows
Seafloor
boulders
Faults and
fractures
Seafloor
sediment
variations
“There are no surprises – unless you are not looking!”

18. 18
Gas response on seismic
Bright seismic reflectors that are multiple times brighter than the background can potentially be gas.

19. 19
Mud volcanoes: uplift, poor imaging, gas chimney above it
• Azerbaijan has 1/3 of the world’s mud volcanoes.
• Azeri-Chirag-Guneshli field location has them too.
Drilling risks of a mud volcano:
• Gas presence
• Buried fragile mud flow
Buried Mud volcanoes on seismic

20. 20
Surface Mud volcano on seismic

21. Depth
Pressure
Top of Overpressure
Normal
Pressure
Pore
Pressure
Overburden pressure (OB) / geostatic
pressure: vertical pressure at any point
in the earth. It’s a function of the mass of
rock & fluid above the point of interest.
Normal Pressure /hydrostatic
pressure: pressure of brine (water +salt)
in the pore space.
Pore pressure (PP): pressure of the fluid
in the pore space.
Overpressure: difference between
normal pressure and pore pressure.
Overpressure
Formation Pressures 1
21

22. As load is applied, if fluid is not
allowed to escape, the pore fluid
supports the added overburden
load, and pore pressure increases.
As excess pore pressure bleeds off
through natural permeability, the
load is transferred to the rock frame
resulting in compaction and
porosity reduction.
22
Overpressure: Compaction Disequilibrium

23. 23
Formation Pressures 2
Fracture pressure (FP): pressure higher
than which rocks lose their strength and
fracture. It is a function of PP & OB.
Drilling window: pressure interval
between pore & fracture pressures.
P>FP:
• lost mud (P) into the formation (FP)
• fluid pressure (P) from 1 formation
fracking the other (FP)
P<PP:
• fluid/gas from formation (PP) enters the
wellbore (P)
Depth
Pressure

24. 24
Pressure
inside well
at h
Ending up underbalance
Underbalance: a condition when pressure
inside wellbore (at certain depth) is less than PP.
What can happen when underbalance (P<PP)?
• Kick/well control
• At shallow depth with poor cementing fluid
from the underbalance depth can reach the
seabed (broaching)
• Broaching can cause a major risk to staff &
integrity of well & drilling rig
Depth
Pressure
Pore
pressure
at h
h

25. Shallow Gas
Loss of well & platform Integrity

26. Shallow Gas: Definition
Drilling Geohazards is responsible for shallow section aka top-hole which is
max up to 1000m TVDSS that is drilled without a blowout preventor.
Shallow Section:
− The geological section above the setting depth of the first pressure
containment casing string in a well.
• Shallow Gas Blowout
− An incident where shallow gas is released from the well after a gas zone
has been penetrated before the first pressure containment casing string
has been set and the BOP has been installed on the well.
26

27. Top-Hole Drilling: the “Shallow” section
Conductor (e.g. 36”)
• Drive
• Drill & Grout
• Jet
Optional
Intermediate Casing (e.g. 28”)
• Drill & cement
First Pressure Containment String
(e.g. 22, 20” etc.)
• Drill & cement
Not to Scale!
Blow Out
Preventer
and Riser
Drilling has
higher risk until
setting BOP

28. Shallow Gas: Definition
• Shallow Section:
− The geological section above the setting depth of the first pressure containment casing
string in a well.
• Shallow Gas Blowout
− An incident where shallow gas is released from the well after a gas zone has been
penetrated before the first pressure containment casing string has been set and the
BOP has been installed on the well.
• Shallow Gas suggested definition:
− Any gas charged interval (e.g. sands) lying in the overburden interval
above the setting depth of the first pressure containment string and prior
to the BOP being installed on the well.
28

29. CP Baker: Aftermath, GoM, 1964
• Cause

30. Shallow Gas Blowouts: Global Spread
30
Trinidad
Azerbaijan
Turkmenistan
US: GoM
Beaufort Sea
Canada
Mid-Norway
Nigeria
Barents Sea
North Sea: UK, Norway
Denmark and Germany
Brunei
Indonesia
India
China, Bohai Bay
Congo
Mexico
Peru
Venezuela
Qatar
Saudi Arabia Thailand
US: CA
US: Alaska
Cook Inlet
Global Marine Blowout database. Note data are not absolutely inclusive!!!
Egypt
Cabinda
Angola
Recorded Blowouts
Blowouts with fatalities
South Korea

31. Shallow Gas Blowout Statistics
Area Blowouts All Causes Shallow Gas Blowouts
Number % Number %
Global
All Water
Depths
593 100% 151 25%
To end 2011, SINTEF Global Offshore Blowout Database

32. Top-Hole Pore Pressure: Gas Implications
Normally
Pressured
Top-Hole
“Over
Pressure”
Build
• In the vast majority of settings the
top-hole section is normally
pressured (i.e . “normally pressured”
shallow gas)
• In the Caspian Basin overpressure
starts close to seabed!
• A check should be made against the
predicted pressure regime by
working with a PPFG specialist.
Overpressured
Caspian
Top-Hole

33. Pressure impact of a Shallow Gas Column
• A significant number of shallow gas
blowouts have occurred in a
normally pressured section where a
significant gas column was
unexpectedly encountered.
• Note the impact on the pore
pressure profile, above the normal
pressure trend, due to the presence
of a 50m gas sand.
• Shallow Gas predictions should not
only highlight the potential
presence of gas but also, where
possible, the apparent column
height.
Increase in Pressure
from Gas column
~0.1sg or ~0.5ppg

34. Normal Pressure: Unpredicted Shallow Gas
…crossflow and
charge of exposed
shallower
aquifers…..
Conductor installed.
Top-hole section drilled
with seawater and
sweeps expecting
normally pressured
section
Significant unexpected
gas column
Aquifer
Aquifer
Not to Scale!
Uncontrolled flow at the wellhead up
through water column!!!
Effective pressure of gas column
exceeds pressure of water column
and cuttings, upward flow of gas
starts….

35. Potential Result
Large Stratigraphic Trap Mid-Norway, 1985
Large Structural Trap, CNS, UK, 1990

36. Top Hole section drilled with light
mud weight!!
Jack-up rig: Shallow Gas Implications
Not to Scale!
Gas Sand
Aquifer
Significant unexpected
gas column
Top-hole drilling with diverter in
place!!
Conductor driven.
But allows returns to the drill floor!!

37. Jack-up rig: Shallow Gas Broach Risk
Not to Scale!
Gas Sand
Aquifer
Significant unexpected
gas column
Mud is pumped into the well to
counter and kill the gas flow….
Mudweight exceeds fracture
strength at conductor shoe –
potentially leading to broach!

38. Jack-up rig: Shallow Gas Broach and Collapse
Not to Scale!
Gas Sand
Aquifer
Loss of seabed support leading to
rig collapse!
At least five global examples!!!

39. Jack-up rig: Shallow Gas Fault Scenario
Not to Scale!
Gas Sand

40. Jack-up rig: Fault Cross FlowBreakout
Not to Scale!
Gas Sand
Gas cross flow and escape to seabed
via fault!

41. Shallow Gas: failure in cementing or isolation
Broach
Not to Scale!
Slightly Overpressured Gas Sand
Balance maintained in drilling to section TD,
pumped out of hole, well still not flowing. Run in
with casing and pumped cement. As cement sets
up weight loss allows inflow of gas and channels
to form in cement!

42. Shallow Gas: Drilling Mitigations
Not to Scale!
Gas
Top-set, drill with
BOP protection
Gas
Drill with sacrificial
PAD mud
Gas
Drill verification
12 ½” Pilot Hole
Gas
Identify, communicate,
move and avoid!
Seabed
Safe Offset
Distance

43. Reasons for shallow gas prediction failure
• No data
• Poor Data
• Forgotten Lessons
• Poor Front End project planning
• Inadequate Study Area
• Data not looked at properly
• Data: seismic images, drilling experiences,
logs, pressure data

44. Shallow Gas Summary
• Of all the marine Geohazard issues Shallow gas has resulted in the single largest loss of life.
• Initially risk was due to absence of any image to predict shallow gas presence
− Subsequently data improved
− Further events provoked further improvements in acquisition, processing and analysis
• Shallow gas remains a significant global shallow hazard risk and needs to be properly
addressed!

45. Shallow Water Flow

46. Shallow Water Flow (SWF): Definition
Overpressured geological interval from which pore water flows into a well causing
difficulties in well control and effective cementing of casing.
SWF is a global phenomenon in high deposition rate environments and not limited to
deep water.
Because of high depositional rate, fluid trapped in the pores doesn’t have enough
time to escape thus causes compaction disequilibrium
It results high pressures being trapped which can be released in underbalance
condition
46

47. SWF: Global Spread
47
Cairn, KDG India
BP, Trinidad, 2003
BP, Foz do
Amazonas
SOCAR & BP
Azerbaijan
BP & others
Nile Delta
Various Operators
GoM
Beaufort Sea
Canada Statoil
Mid-Norway
Various Operators
Nigeria

48. SWF: what it might mean to operations (i)
Not to Scale!
Slightly Overpressured Aquifer
…or uncontrolled flow at
the wellhead!
…crossflow and charge
of shallower
aquifers…..
Excessive mud
pressure to overcome
SWF could break
down conductor shoe
and broach to surface
Inadequate mud
weight to prevent SWF
could allow flow to
broach around
conductor...

49. Shallow Water Flow while drilling
Drill pipe
Shallow water flow
A case of riserless
drilling while
underbalanced to pore
pressure

50. SWF: what it might mean to operations (ii)
Broach
Sand
Mining
Casing
Collapse
Not to Scale!
Slightly Overpressured Aquifer

51. Shallow Water Flow: Drilling Mitigations
Not to Scale!
Seal
Aquifer
Case off weaker
formations, drill with
BOP and weight up
Aquifer
Drill with sacrificial
weighted “Pump and
Dump” (PAD) mud
Aquifer
High ROP, load annulus
with cuttings “make own
mud!”
Seabed
Aquifer
*Dual Density Drilling
with seabed mud
recovery pump
*Dual Density drilling (riserless) gives better flexibility to fit into the drilling window (between pore & facture pressure)

52. Seal
Pre-Drill Mitigation: Deep Geotechnical Borehole
Not to Scale!
Aquifer
Drill Borehole with
Piezoprobe to verify PPFG
trend above suspected
SWF aquifer
Seabed
Seal
Aquifer
Design and implement
safe well, casing and
cementing plan
Identify overpressure
trend above hydrostatic
Pressure

53. Geological risks

54. Caspian shales/soil units
• Shallow soil units are chemically reactive
• They swell, cause tight spots when drilled
underbalanced or with water-based mud
• Bit balling (when clay plugs nozzles and bit teeth)
In Gulf of Mexico top-hole is drilled with seawater
(fast and cheap) while in the Caspian basin oil-based
mud is used!
• Tight spots cause stuck pipe, casing running
problems, ruins cement volume calculations
• Correct mud density with inhibitors can prevent
reactivity

55. Marine Geohazards Summary
• Marine Geohazards studies are undertaken to identify hazards
to allow risks to be mitigated by avoidance or adoption of safe
engineering practices.
• Without this we have seen there is the risk of:
• Significant loss of life
• Damage to the environment
• Significant project cost overruns
• Deferred, or permanently lost, production
• Significant impact to corporate or industry reputation

56. Thank you!