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The operator’s objective was to drill a 2,460 ft (750 m) horizontal section through a reservoir interval with a diameter of 9.5 in., ensuring a high-quality well without formation damage, imparting wellbore stability avoiding any fluid losses.

The reservoir is in a post-salt oil field located in the Santos Basin 115 miles (185 km) off the shore of Rio de Janeiro, in 5,079 ft (1,548 m) of water depth.

The reservoir is formed by very high porosity and unconsolidated sandstone with an average porosity of 38% and a high permeability of 5 darcies with an extra heavy crude oil of 14° API. The oil has a very strong acid character that, in the presence of mud filtrate, can cause formation damage.

Twice competitors had attempted to drill and test the well, resulting in a damaged reservoir with high skin damage and a low productivity index (PI) of 4.0 m3/d/Kgf/cm2. A drill-in fluid was used to drill offset wells in order to provide borehole mechanical stability, resulting in equivalent circulation densities (ECD) above 10 lb/gal (1,198.3 kg/m3).

As a result of the high ECDs, massive downhole lost circulation around 120 bbl/hr (19 m3/hr) was experienced, resulting in an average of 4,780 bbl (760 m3) of fluid lost.

Significant lost-circulation materials with different concentrations were used without success.

Losses caused by the fluid’s inability to reach total depth (TD) during the second attempt to drill the well again required abandonment.

Based on information from both of the offset wells and reservoir characteristics, Baker Hughes, a GE company (BHGE), customized its MAX-PRIME™ reservoir drill-in fluid solution (RDIF) with the PERFFLOW™ water-based RDIF, which is specially formulated to overcome challenges similar to those encountered on this project.

Download the PDF to read the full case study.

Challenges & Results
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Challenges

  • Ultradeepwater well at 5,079 ft
  • Sandstone reservoir with high permeability of 5-6 darcies and porosity at about 38%
  • Narrow operational window with high risk of lost circulation and formation collapse
  • Unsuccessful attempts in two offset wells with severe fluid losses, resulting in high skin damage and low PI
  • Drill and condition the well without fluid losses
  • Avoid formation damage and maximize PI
  • Ensure gravel packing operation occurs without fluid losses

Results

  • Drilled and conditioned well without formation losses
  • Reduced overall drilling NPT
  • Increased wellbore stability by allowing higher ECD values
  • Performed gravel packing operation without formation losses
  • Avoided reservoir damage
  • Custom particle size distribution minimized skin damage
  • Maximized reservoir production (productivity index was greater than offset wells)