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Deep water (awel 7aga)

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Ahmed Hamdy

on 19 October 2012

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Transcript of Deep water (awel 7aga)

Introduction Mechanism Problems Deep water Drilling Problems and Solutions Done By:
Ahmed Hamdy
Amira Taha
Eman Abed
Mohammed Magdy
Mostafa Tarek
Hesham Sayed Summary World Deepwater Areas Technology Maturity History Introduction Deep Water Drilling : Water Depths more than 400m

Ultra Deep Drilling : Water Depths more than 1500m

Deep Water exploration drilling costs > 50 mill $

Oil investment analyst D. Barry McKennitt said the only reason anyone is willing to drill in deepwater with the depths, temperatures, and other significant technical challenges is that other opportunities are closed. "They don't do it just for exercise," he said. Deepwater Forefronts Physical Effects in Deepwater How? Drillship 3000m depth capacity

High mobility

High deck load capability

Reduced logistics

Crude storage & offloading capability Semi-submersible 2500m depth capacity

Good stability

Reduced motion

Better station keeping

Low operating costs Drill Ship Semi-submersible Deepwater Drilling Rigs Low Temperature:

Hydrate formation with plugging of control and flow lines

Wax deposition with reduction of pipe area and pressure loss Pressure Effect:

Risk for riser and pipeline collapse

Intrusion of water in control systems

Limited possibility to depressurise systems for hydrate removal Length Effect:

Increased weight and loading on risers, umbilical and mooring
Higher hang off forces on floaters
Increased flexibility of risers and tethers
Natural period of movements increases Physical Effects in Deepwater i)Gas hydrates Occurrence :
Four elements necessary to form and stabilize gas hydrates;
the hydrocarbon phase
the aqueous phase (the water in OBM can also form hydrates)
low temperature
high pressure Hydrates problems

Gas hydrates

Hydrates in sediments ii)Hydrates in sediments the main problem is associated to gas in underlying formations
unstable if drilled through
possible hazard
creates gas blow out
blocking of the BOP connector Solutions hydrate simulators and modeling programs

selection of mud system; WBM or SBM

chemical inhibitors added to drilling fluids

thermodynamic inhibitors (salt, glycol) to change equilibrium conditions of hydrate formations

kinetic inhibitors (polymers, poly-butylene glycol) to retard the formation of hydrates Gas hydrates & well control Constraints :
hydrates can plug the choke and kill lines, BOPs and riser
dehydration of drilling fluids and / or cement Hydrates solid ice-like mixture of gas and water at high pressure and low temperature

1 cubic feet of hydrate crystal contains approximately 170 SCF of gas Hydrates Solutions
Casing While Drilling (CWD)

Dual Gradient Drilling (DGD) By Using DGD A 6” return line with ~36 bbls/1000 ft can do the job

Requires much less weight and volume for storage!

A smaller vessel can do the job.

A smaller vessel can easier be upgraded to do the job. By Using DGD Conventional Method Effect of Increasing Water Depth Weight of drilling riser increases with depth

21-inch riser has an internal capacity of ~ 400 bbls/1,000 ft

At 10,000 ft, wt. of riser ~ 2 million lbs. and wt. of 17.1 ppg mud inside riser ~ 2.7 million lbs

More storage space required on drilling vessel

Larger and more expensive drilling vessel is required Dual Gradient Drilling
Concept Pressure inside wellbore at seafloor is ~ the same as the pressure in the ocean at seafloor

No Conventional Drilling Riser

Mud Return Line

A “Dual Mud Density System” Water Depth Shallow water
flow Subsalt Drilling How it works 1-trapped water at very high pressure

2-overlayed by impermeable formation

3-when breached this water with high pressure starts to flow to surface How to avoid shallow water flow Improved site surveys and data
Use foamed cement to stop flow
Use dual gradient technique
Use foamed cement to stop flow(injected)
Use dual gradient technique
Use weighted mud till reach to surface with return to sea floor(expensive) but sometimes considered as most cheap and safest solution
Seismic or sonar at well head can have great help
Annular pressure while drilling Considered as most dangerous problem

Not easy to predict ,detect or controlled

No efficient firm solution for this problem

May cause losing of well and sometimes the whole subsea infra-structure Shallow water flow solution Try to know upnormal pressure zones prior to drilling
They gave low seismic velocity so velocity considered to be indication of salt zones
Vsp near wells can give direct indication for velocity in salt formation problems Sudden increase in pressure may cause kicks and if not controlled may cause blowouts Sub salt drilling Under any salt formation there is always high pore pressure ramps
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