Schlumberger

Case Study: HISIDE Blender Unit Helps Operator Get the Surface Casing to Depth in an Uncertain Environment

Challenge: Shell Oil Co. needed to drill a 12 1/4” pilot hole to a depth of 7,740 ft (2,360 m) prior to actual spud in order to assess the likelihood of shallow water flow and to retrieve pore pressure data.

Solution: The rig was unable to deliver the required seawater for effective operation of the unit.

Result: 1. The 12 1/4 “ pilot hole was drilled to a depth of 7,200 ft (2,195 m) with no shallow water flows. 2. The 42” conductor hole was drilled to a TD of 4,970 ft (1,515 m). 3. The 26” hole section was drilled with seawater and high viscosity sweeps to a depth of 6,817 ft (2,078 m) and with 1.25 sg diluted killmud to TD of 7,740 ft (2359 m). 4. The unit allowed 9,921 bbl (1,183 m³) of 1.97 s.g. kill mud to be blended with 25,600 bbl (3,053 m³) of seawater to make 35,525 bbl (4,236 m³) of 1.25 s.g. mud during the operation. 5. The project finished 17 days ahead of schedule.

The use of the HISIDE Blender unit enabled the client to safely and economically get the surface casing to depth in an uncertain environment. The ability to adjust mud weights in a quick and efficient manner allows the client to drill in these areas with a level of confidence that any problems can be dealt with quickly and efficiently. At the end of the running and cementing of the 20” casing, the Gro Prospect was 17 days ahead of schedule. A great deal of that performance was due to the rig crews and the hard work they put in to overcome the problems that were incurred.

Below is a list of some things that should be considered when installing and operating a HISIDE Blender unit:

  • The HISIDE unit discharge should be in a separate pit from the mud pump suction in order to have a sufficient supply of blended mud to avoid shutdowns and allow for a smoother operation. It also provides for a more homogenous mixture of the mud.
  • It is preferable to have the unit and the supply lines mounted in a horizontal position. On the Leiv Eiriksson, the mud supply line and flow meter was mounted vertically and the meter did not work reliably at lower flow rates. The seawater lines were mounted horizontally and worked fine with lower flow rates.
  • The mud must be delivered to the unit in sufficient quantity and pressure to overcome the backpressure from the seawater side of the unit. On the Leiv Eiriksson, we were unsuccessful in trying to blend the mud as it was delivered from the boat because of insufficient pressure. Although the volume was fine, the pressure could not overcome the pressure from the seawater side.
  • A thorough knowledge of the rig and boat capabilities should be determined before installing and operating the unit. Can mud be taken from the boat and the pontoon tanks at the same time? Can the rig be able to deliver the mud from the pontoons at a sufficient rate to avoid shutdowns? Can the boat do the same? Is their sufficient surface volume to ensure a smooth operation?

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"The use of the HISIDE Blender enabled the client to safely and economically get the surface casing to depth in an uncertain environment several days ahead of schedule.”
Ricky Livingston
Mud Engineer
M-I SWACO