TAMU Pemex Offshore Drilling

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TAMU - PemexOffshore Drilling
Lesson 12A Shallow Water Flows
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Shallow Water Flows (SWF)

• What is a SWF?
• Where do SWF occur?
• Why do they occur?
• How common a problem is this?
• How serious is this problem?
• Standard drilling procedures
• Some potential solutions to the SWF problem

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References

• Shallow water flows How they develop what to
  do about them, by William Furlow, Offshore,
  September 1998, p.70.
• Acrylate momomer solution stops artesian
  water, geopressured sand flows, by Larry Eoff
  and James Griffith, Oil Gas Journal, November
  2, 1998, p.89.

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References, contd

• OTC 1997
• Deepstar report, 1996.
• Shallow Water Flow Forum, June, 1998.

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What are Shallow Water Flows (SWF)?

• Shallow water flows are flows from overpressured
  sands encountered at shallow depth below the mud
  line in deepwater regions of the world.

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What is a Shallow Water Flow?

• Sometimes sand flows with the water. Flow rates
  as high as 25,000 bbls/day have been reported
  (730 gal/min).
• A video presentation at the Shallow Water Flow
  Forum (June, 1998) showed a SWF producing plumes
  of sand and debris that boiled up 60 ft from the
  seafloor.

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Where do SWF Occur?
SWF typically occur in water depths beyond 1,500
ft, at depths ranging from 300 to 3,500 ft below
the mud line. SWF represent a recently
encountered phenomenon in the Gulf of Mexico,
West of the Shetlands, the Norwegian Sea,
Southern Caspian Sea, and the North Sea.
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Where in the well do SWF Occur?
Seawater Hydrostatic
Aquifer Pore Pressure
Depth
Shale
Sand
Pressure
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Why do SWF occur?

• Basically SWF occur because the pressure in the
  wellbore is lower than the pressure in the
  aquifer.
• The flow rate can be very high because of
• ?thick, high- permeability sands
• ? low water viscosity, and
• ? sufficient pressure differential.

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How common a problem is this?

• It has been suggested that 30 to 40 of all
  deepwater wells in the Gulf of Mexico encounter
  this problem.
• Once the flow begins it is very difficult to
  stop. This makes it difficult, and sometimes
  impossible, to get a good cement job around the
  casing.

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How serious is this problem?
Hole erosion and poor cement jobs can result in
settling of the casing strings, accompanied by
buckling of inner casing strings, leading to
serious damage or loss of well (10-20
million?). At Ursa a number of wells were washed
out, and had to be relocated. Total cost is
estimated to be around 150 million!
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EROSION
SAND
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Typical drilling procedules - SWF

• 1. Jet in 30-in drive pipe to 300 ft below mud
  line. Do not cement. Silt forms seal.
• 2. Drill and under-ream hole to 600 ft. Run 26-in
  
• conductor pipe and cement to mud line.
• 3. The next casing string would normally be
  20-in. This string might be run to 1,500 ft.,
  etc.
• Where there are no SWF present the 26-in and
  20-in strings may be run much deeper. Some string
  sizes may be eliminated.

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(No Transcript)
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• Step 1a. Jet in 30-in conductor to 300 ft
• below mud line

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Step 1b. 30-in conductor silts in - no
cementing
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Step 2a. Drill, under-ream hole for the 26-in
conductor
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Step 2b. Cement the 26-in conductor to the mud
line
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Any solutions to the SWF problem?Soln 1.
Increase the mud weight

• When encountering any overpressured zone,
  standard practice is to increase the density of
  the drilling fluid. This increases the pressure
  in the wellbore to the point where influx (SWF)
  should cease.
• Sometimes increasing the the mud weight may lead
  to lost circulation, and the influx continues,
  possibly turning into an underground blowout.

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Soln 1. Increase the mud weight
Seawater Hydrostatic
Fracture Pressure
Pore Pressure
Depth
Shale
Sand
Pressure
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Soln 1a. Increase the mud weight Install
riser - May lead to lost circulation
Seawater Hydrostatic
Drilling Riser
New Mud Hydrostatic
Fracture pressure
Pore Pressure
Depth
Shale
Sand
Pressure
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Soln 1b. Increase the mud weight - drill
with returns to the seafloor
Seawater Hydrostatic
New Mud Hydrostatic
Fracture pressure
Depth
Shale
Sand
Pore Pressure
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Soln 1c. Increase the mud weight - drill with
returns to the seafloor - and pump the mud
to the surface
Seawater Hydrostatic
New Mud Hydrostatic
Fracture pressure
Depth
Shale
Sand
Pore Pressure
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Soln 1c. Increase the mud weight (zoom)
- drill with returns to the seafloor
- and pump the mud to the surface
(Riserless Drilling)
New Mud Hydrostatic
RBOP
Fracture pressure
Sand
Pore Pressure
Pressure
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Soln 2. Use a seafloor diverter

• The diverter is a pack-off device, attached to
  the casing, that can put back-pressure on the
  formation to stop the SWF.
• It may work, if the casing is set just above the
  aquifer,
• but may result in lost circulation, and possibly
  broaching to the surface.

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Soln 2. Use a seafloor diverter
New Mud Hydrostatic
Fracture pressure
Sand
Pore Pressure
Pressure
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JIP Shallow Water Flow Diverter

• Rotating Head
• and
• Drilling Choke

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Rotating Head and Drilling Choke
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Soln 3a. Use a chemical grout
This treatment is designed to plug off the pore
space in the aquifer. It also consolidates the
sand. After chemical solidifies, drilling can
proceed.
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Step 3b. Use a chemical grout contd
AMS acrylate monomer solution AMS is
effective in downhole temperatures from 50 to 200
deg. F.
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Soln 4. Foam Cementing

• Low-density foamed cements have sometimes been
  successful in stopping SWF.
• These are especially successful when used in
  combination with chemical grouts.
• Grout, drill, run casing, cement.

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Shallow Water Flow Cementing Technology

• Settable Spots
• By-passed fluid and filter-cake solidify and seal
  formation

• Foamed Cements
• Variable hydrostatic gradient possible
• Lightweight , high strength
• Expands to fill annulus
• Conforms to borehole
• Fast setting at low temperature
• High shear bond supports well loads

WATER FLOW
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Jet Stabilization Process
Place Cement Slurry, Resin, Or Other Stabilizing
Material in Enlarged Hole

• Slurry is jetted against wellbore
• wall at high velocity
• Ensures enlarged wellbore is filled
• with slurry
• Displaces drilling fluid and spacer
• Creates intimate contact between
• slurry and wellbore
• Removes filter cake

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Jet Stabilization Process
Pull out of cement and circulate to clean up
drill pipe
Wait for Cement to Set
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Jet Stabilization Process
Stabilized/Reconstituted Wellbore
Drill through cement and continue making hole
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Soln 5. Underbalanced drilling through the SWF
zone using coiled tubing
A joint industry project is underway to evaluate
and develop this technique.
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6. Drive the conductor through the SWF zone
Eliminates the annulus where the water can flow.
500-1,000 ft BML is feasible.
Seawater Hydrostatic
Aquifer Pore Pressure
Depth
Shale
Sand
Pressure
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DRILL DRIVE
Drilling Jar
Connection
Driving Tool
Flow Thru Holes
Conductor Adapter
Connection
Shear Pins
Mud Motor
Connection
Drill Bit
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Hammer
Casing
Anvil / Striker Plate
Cushion

Assembly
Drive Ring
Drive Point
Bottom-Driven
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6. Drive the conductor through the SWF zone
Eliminates the annulus where the water can flow.
Penetration to 500-1,000 ft BML is feasible in
almost all cases. 500 ft of drive pipe provides
sufficient resistance to support the weight of
all the subsequent casing strings, thereby
preventing settling and casing buckling, even if
SWF reoccur.