Confidential to SMD JIP Subsea Mudlift Drilling Basic Technology by Julie Zhang and Hans Juvkam-Wold November 2000 Lesson 4 Similar to conventional -- brief description of key elements in a good balanced cement plug operation U-tube effects -- need to show how/where the calculations are impacted by U-tube considerations (link to a calculation display?) Need to link to graphic of the cement U-tube? Does our existing graphic work or do we need something different? U-tubing Concepts 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP Contents U-Tube Concept in Conventional Drilling U-Tubing in DGD Equilibrium After U-Tubing Factors Affecting U-Tubing rate Effect of Water Depth, Mud Weight, Mud Viscosity, Pipe Size, Nozzle Size and Well Depth Below Mud Line Hookload during U-tubing Special considerations Examples of U-Tubing 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP U-tube in Conventional Drilling Drilling, under static conditions, with uniform mud weight throughout, the hydrostatic head in the drillstring and annulus are equal. The U-Tube is therefore balanced. However, there are exceptions. Such as: At beginning of increasing mud weight. Cementing Lots of cuttings in annulus Gas in annulus Drillstring Riser Mudline Annulus 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP Subsea Mudlift Drilling BOP Thus, the well can be treated as a U-tube 4. U-tubing Concepts Confidential to SMD JIP

When does free-fall (U-tubing) occur? During pipe connection Pipe trips in or out of the hole Wiper trip Logging/Gyro NOTE: U-tubing will occur only when there is no drillstring valve (DSV) in the drillstring 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP U-tube in DGD Sea water In DGD, the pressure at the inlet to the subsea mudlift pump is maintained ~ at seawater hydrostatic pressure Sea water Hydraustatic Thus, pressure inside drillstring and outside drillstring are not statically balanced 4. U-tubing Concepts Confidential to SMD JIP

Annulus and Return Line Confidential to SMD JIP Static Pressure - DGD Annulus and Return Line Drillstring pressure Balance Depth Mud level Seawater Hydraustatic Pressure Pressure 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP U-tube in DGD When the rig pump is shut down, Free-Fall or U-Tubing occurs in DGD . . . because the pressure at the inlet to the subsea mudlift pump is maintained ~ at seawater hydrostatic pressure Drillstring Mudline Annulus 4. U-tubing Concepts Confidential to SMD JIP

Final Equilibrium Condition in DGD The final mud level depends on two factors: 1. The relative densities of mud and sea water 2. Water depth Seawater Hydraustatic balance Balance Mudline Mud level Annulus Pressure 4. U-tubing Concepts Confidential to SMD JIP

Final Equilibrium Condition in DGD Below the mudline the pressures are balanced inside and outside the drillstring. Above the mudline the height of mud inside the drillstring is essentially balanced against a column of seawater. Mud level Pressure 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP Base Case Assumptions for Simulator Runs (made with Dr. Choe’s DGD Simulator) Water Depth 10,000 ft (Range 4,000 - 10,000) Mud Weight 15.5 lb/gal (Range 11-18) Mud Viscosity 111/65 (Range 2/1 - 400/300) Drillpipe ID 4.762 in (Range 2 - 6) Nozzle Sizes 16/32 in (Range 12/32 - 24/32) Well Depth 20,000 ft (12,000 - 20,000) Balance 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP U-tubing Rate in DGD Initial Circulation Rate - before rig pump shutdown Dynamic effects as the fluid rapidly slows down Decreasing Flow Rate - as the fluid level drops - and the driving head decreases Balance Flow changes from turbulent to laminar Mud level Approaching Static Fluid Level Pressure 4. U-tubing Concepts Confidential to SMD JIP

Factors Affecting U-Tube Rate in DGD Water Depth Mud Weight Mud Viscosity Drillpipe ID Nozzle Sizes Well Depth Below Mud Line 4. U-tubing Concepts Confidential to SMD JIP

Effect of Water Depth on Free-Fall Rate Water depth is one of the driving forces behind the u-tube. As water depth increases: The u-tubing rate increases The final fluid level in the drillpipe is lower The time to reach equilibrium increases 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP U-Tubing Rate vs. Time for Various Water Depths 4. U-tubing Concepts Confidential to SMD JIP

Effect of Mud Weight on U-Tubing Rate Mud Weight is the other driving force behind the u-tube. As mud weight increases: The u-tubing rate increases The final fluid level in the drillpipe is lower The time to reach equilibrium increases 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP Mud Level in Drillpipe vs. Time for Various Mud Densities 4. U-tubing Concepts Confidential to SMD JIP

Effect of Mud Viscosity on U-Tubing Rate Mud Viscosity is one of the factors that influences the u-tubing rate. As mud viscosity increases: The u-tubing rate decreases The time to reach equilibrium increases 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP U-Tubing Rate vs. Time for Various Mud Viscosities 600/300 RPM 4. U-tubing Concepts Confidential to SMD JIP

Effect of Drillpipe ID on U-Tubing Rate Drillpipe ID is another factor that controls the u-tubing rate. As the drillpipe ID increases: The u-tubing rate increases (less friction) We might expect that the time to reach equilibrium would increase (more mud to drain), but this is not necessarily so - see graphs 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP U-Tubing Rate vs. Time for Various Drillpipe IDs 4. U-tubing Concepts Confidential to SMD JIP

Effect of Nozzle Sizes on U-Tubing Rate Nozzle Size is another factor that controls the u-tubing rate. As the nozzle size increases (3 nozzles assumed): The u-tubing rate increases The time to reach equilibrium decreases 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP U-Tubing Rate vs. Time for Various Bit Nozzle Sizes 4. U-tubing Concepts Confidential to SMD JIP

Effect of Well Depth BML on U-Tubing Rate Well Depth BML is yet another factor that affects the u-tubing rate. As the depth below mudline increases: The u-tubing rate decreases (more friction) The time to reach equilibrium increases 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP U-Tubing Rate vs. Time for Various Wellbore Depths 4. U-tubing Concepts Confidential to SMD JIP

Pit Gain during U-tubing During U-tubing, quantities of fluid will return to surface and may appear to be pit gain (kick!). For instants, in 10,000 ft water depth, with 18.5 ppg mud, 6.5 “ DP. Surface pit gain is expected to be 180 bbls at the end of U-tubing process. In 1500 ft water depth, with 14 ppg mud, 5” DP, 11 bbls pit gain are expected. 4. U-tubing Concepts Confidential to SMD JIP

Hookload during U-tubing During U-tubing, Hookload will decrease mainly due to loss of mud inside the drillstring. For the 10,000 ft water depth case, a 120,000 lbf reduction in hookload will be expected at the end of U-tubing. While for the 1,500 ft water depth case, a 2,800 lbf reduction in hookload is expected. 4. U-tubing Concepts Confidential to SMD JIP

Hookload during U-tubing Cont. In a deep-water case, hookload can be used to predict fluid level by simply subtracting the weight of mud u-tubed from the hookload. In a shallow water case, this method can not be used to predict fluid level. 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP Hookload vs. Mud Level at 1,500 ft Water Depth Estimated Hookload considering only the mud level drop 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP Hookload vs. Mud Level at 10,000 ft Water Depth 4. U-tubing Concepts Confidential to SMD JIP

Special Considerations DSV should be installed as often as possible. However, U-tubing still could occur in cases, such as when the DSV does not work properly. After U-tubing, the Drillstring must be filled up with mud before full circulation can be resumed. 4. U-tubing Concepts Confidential to SMD JIP

Special Considerations - Cont. Restriction pipe can be added in the drillstring to allows circulation at lower rates with full drillstring. As length of restriction pipe increases, frictional pressure increases. U-tubing rate decreases. As ID of restriction pipe decreases, frictional pressure increases. U-tubing rate decreases. 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP Some Examples U-Tubing while... Making a 5-minute Connection Making a 30-minute Connection Shutting Down Before Making a Trip Re-Starting After Making a Trip 4. U-tubing Concepts Confidential to SMD JIP

The 5-Minute Connection Circulating Prior to Making the Connection Shut Down Surface Pump U-Tubing in Progress Connection is Complete Restart Circulation 4. U-tubing Concepts Confidential to SMD JIP

Circulating Prior to Making a Connection Confidential to SMD JIP 4. U-tubing Concepts Confidential to SMD JIP

Circulating Prior to Making a Connection Elapsed Time = 0 sec Fluid Level in DP = 0 ft The 5-min Connection Circulating at 700 gpm -both pumps Standpipe Pressure = 5,517 psi 4. U-tubing Concepts Confidential to SMD JIP

Shut Down Surface Pump The 5-min Connection MLP Circulating at 392 gpm Elapsed Time = 30 sec Fluid Level in DP = 237 ft Pit Gain = 4.10 bbls The 5-min Connection MLP Circulating at 392 gpm SP Pressure = 0 psi MLP P_out = 8,237 psi 4. U-tubing Concepts Confidential to SMD JIP

U-Tubing in Progress (1 min) Elapsed Time = 60 sec Fluid Level in DP = 505 ft Pit Gain = 8.83 bbls The 5-min Connection MLP Circulating at 378 gpm MLP P_out = 8,227 psi 4. U-tubing Concepts Confidential to SMD JIP

U-Tubing in Progress (1 1/2 min) Elapsed Time = 90 sec Fluid Level in DP = 755 ft Pit Gain = 12.9 bbls The 5-min Connection MLP Circulating at 365 gpm MLP P_out = 8,218 psi 4. U-tubing Concepts Confidential to SMD JIP

U-Tubing in Progress (2 min) Elapsed Time = 120 sec Fluid Level in DP = 1,005 ft Pit Gain = 17.3 bbls The 5-min Connection MLP Circulating at 351 gpm MLP P_out = 8,208 psi 4. U-tubing Concepts Confidential to SMD JIP

Connection Complete - Start Rig Pump 500 gpm (elapsed time = 5 min) Fluid Level in DP = 2,295 ft Pit Gain = 40.0 bbls The 5-min Connection Pig Pump at 500 gpm MLP at 268 gpm SP Pressure = 0 psi MLP P_out = 8,157 psi 4. U-tubing Concepts Confidential to SMD JIP

Drill Pipe is ~Full - Rig Pump @ 500 gpm (elapsed time = 16 min) Fluid Level in DP = 2 ft Pit Gain = 0 bbls The 5-min Connection Pig Pump at 500 gpm MLP at 404 gpm SP Pressure = 0 psi MLP P_out = 8,245 psi 4. U-tubing Concepts Confidential to SMD JIP

Resume Drilling - Rig Pump @ 500 gpm (elapsed time = 17 min) Fluid Level in DP = 2 ft Pit Gain = 0 bbls The 5-min Connection Pig Pump at 500 gpm MLP at 500 gpm SP Pressure = 1,540 psi MLP P_out = 8,321 psi 4. U-tubing Concepts Confidential to SMD JIP

The 5-Minute Connection Confidential to SMD JIP 700 gpm 500 gpm 4. U-tubing Concepts Confidential to SMD JIP

Shutdown Prior to Making Trip Circulating Prior to Making the Connection Shut Down Surface Pump U-Tubing in Progress U-Tubing is Complete Restart Circulation 4. U-tubing Concepts Confidential to SMD JIP

U-Tubing in Progress (10 min) Elapsed Time = 10 min Fluid Level in DP = 3,699 ft Pit Gain = 64 bbls Prepare for Trip MLP Circulating at 159 gpm MLP P_out = 8,104 psi 4. U-tubing Concepts Confidential to SMD JIP

U-Tubing Complete (25 min) Elapsed Time = 25 min Fluid Level in DP = 4,292 ft Pit Gain = 73 bbls Ready for Trip MLP Circulating at 0 gpm MLP P_out = 8,060 psi 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP Initial Circulation Rate - before rig pump shutdown Dynamic effects as the fluid rapidly slows down Decreasing Flow Rate - as the fluid level drops - and the driving head decreases Balance Flow changes from turbulent to laminar Mud level Approaching Static Fluid Level Pressure 4. U-tubing Concepts Confidential to SMD JIP

U-Tubing Associated with Trip Stop Rig Pump at 0 min. Re-Start at 30 min 700 gpm 500 gpm 4. U-tubing Concepts Confidential to SMD JIP

Pit Gain Associated with Trip Stop Rig Pump at 0 min. Start at 30 min 500 gpm 700 gpm 4. U-tubing Concepts Confidential to SMD JIP

MLP Rate Associated with Trip Stop Rig Pump at 0 min. Start at 30 min Rig Pump @ 700 gpm @ 500 gpm 4. U-tubing Concepts Confidential to SMD JIP

Confidential to SMD JIP Comparison Rig Pump Down Time (min) 2 5 30 Rig Pump Rate (gal/min) 700 500 Max. Fluid Level Drop (ft) 1,005 2,295 4,292 Total Time (min) 4.5 8.3 10.0 16.3 38 46 4. U-tubing Concepts Confidential to SMD JIP

Fluid Level in DP vs. Time Confidential to SMD JIP Effect of Rig Pump Down Time Rig Pump Rate at 500 gpm 2 min 1,000 5 min Connection 2,000 Fluid Level in Drill Pipe, ft 3,000 30 min Connection 4,000 5,000 10 20 30 40 50 Elapsed Time, min 4. U-tubing Concepts Confidential to SMD JIP

What about Shallower Water Connections? U-tubing depth is reduced Pit gain is reduced Time to reach equilibrium is reduced Time to fill drill pipe is reduced 4. U-tubing Concepts Confidential to SMD JIP

~SEAWATER HYDROSTATIC PRESSURE Confidential to SMD JIP U-Tubing in DGD FLOATER ~SEAWATER HYDROSTATIC PRESSURE 10,000’ STATIC FLUID LEVEL BOP MUDLIFT 20,000’ 4. U-tubing Concepts Confidential to SMD JIP 23

Confidential to SMD JIP Subsea Mudlift Drilling Basic Technology by Julie Zhang and Hans Juvkam-Wold November 2000 The End 4. U-tubing Concepts 4. U-tubing Concepts Confidential to SMD JIP