Case Study: PRIMO-SCREEN System Achieves 20:80 OWR for Optimized Openhole Gravel-Pack Completion

Operator uses system to land premium mesh screen with no drag issues, losses, or hole instability in offshore ERD well, Gulf of Guinea

Challenge: Enable optimal screen running for challenging openhole gravel-pack completion in extended-reach offshore well located in environmentally sensitive region.

Solution: Deploy PRIMO-SCREEN low-oil/water-ratio screen running system to achieve low oil/water ratio (OWR) while maintaining an oil-continuous invert-emulsion drilling fluid system.


  • Achieved OWR of 20:80 and low coefficient of friction (COF).
  • Protected sensitive shale stringers.
  • Landed premium mesh screen with no drag issues, losses, or hole instability.
  • Separated system on rig for proper disposal.

Perform high-quality, low-HSE-impact openhole gravel-pack completion

An operator faced a number of challenges while drilling its Ceiba-39 well in the Gulf of Guinea offshore West Africa. The extended-reach well ran the risk of high torque and drag during completion. The reservoir section contained reactive shale stringers and interbedded shales. Because of the region’s environmental regulations, the screen running fluid had to be treated and disposed on location, not discharged overboard.

The 8 1/2-in × 9 1/2-in section was reamed using a 9 1/2-in Rhino integrated borehole enlargement system and the RHELIANT PLUS organophilic, thermally stable, flat-rheology invert-emulsion drilling system containing SAFE-CARB ground marble bridging agent. The openhole section was completed with medium-mesh screens, 30:50 proppant, and 10-lbm/galUS [1,198-g/L] completion brine containing SAFE-BREAK nonemulsifier.

The 300-um-rated sand control screens were a concern because bridging or drilled solids particles eroded by the proppant carrier fluid at an expected size of approximately 42.9 um could plug the screen, impeding production and potentially limiting the life of the completion.

Because the openhole gravel-pack completion system included a differential-pressure-actuated circulating valve on the lower completion, acid could not be pumped for the filtercake removal process. A water-base pill such as a hydroxyethylcellulose (HEC) solid-free pill for running the screen could not be used because its presence on the invert-emulsion filtercake would cause the brine to interact with the filtercake and formation, causing wellbore stability issues in addition to high torque and drag. Rig time is expensive on offshore operations, and for this job, the operator sought a dedicated screen running fluid.

Deploy PRIMO-SCREEN system with RHELIANT PLUS system

M-I SWACO proposed using the PRIMO-SCREEN system, which uses PRIMO-SURF low-oil/water-ratio invert emulsion system primary emulsifier to achieve an OWR as low as 20:80 while maintaining an oil-continuous invert emulsion. The increased water content enables high-density, solids-free invert-emulsion fluids to be feasible options for screen running fluid. Because a synthetic-base mud was used to drill the reservoir section, displacing the open hole to the PRIMO-SCREEN system mitigated the risks associated with wellbore instability, torque, and drag. The invert-emulsion feature of the PRIMO-SCREEN system would also protect the sensitive shales in the reservoir section.

Run screens with no loss, drag, or instability issues

For the Ceiba-39 well, M-I SWACO engineers used an 11.32-lbm/galUS [1,356-g/L] calcium chloride brine to formulate the PRIMO-SCREEN system fluid to a density of 10.3 lbm/galUS [1,234 g/L] with an OWR of 20:80. Laboratory prequalification testing demonstrated that even with the 20:80 OWR, the PRIMO-SCREEN system was oil continuous and stable at 200 degF.

To demonstrate PRIMO-SCREEN system performance, M-I SWACO engineers prepared two 16-h dynamic HPHT filtercakes built on aloxite media using the RHELIANT PLUS drilling fluid system. The first filtercake was placed in a dynamic HPHT cell with a water-base solids-free pill containing HEC. The second filtercake was placed in another dynamic HPHT cell that included the PRIMO-SCREEN system. The water-base system demonstrated a significant increase in fluid loss as the invertemulsion filtercake was destabilized. The PRIMO-SCREEN system maintained stable controlled fluid loss throughout the test.

After the test, the filtercakes were removed. The PRIMO-SCREEN system maintained the stable invert-emulsion filtercake whereas the water-base fluid system altered the filtercake to a thick and rigid state, indicating that the increased fluid loss had changed the filtercake wettability that could lead to wellbore instability. M-I SWACO used the VIRTUAL HYDRAULICS drilling fluid simulation software to validate that the PRIMO-SCREEN system filtercake demonstrated acceptable equivalent circulating density during placement.

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