Case Study: Integrated Drilling Fluid System Helps Complete 3,000-ft Shale Interval 9 Days Ahead of Plan

High-performance fluid system, sealing additive, and simulation software enable meeting objectives with no fluid-related NPT, stuck pipe, or bit balling, UAE

Challenge: Drill through heterogeneous, highly laminated shale sections in the Laffan and Nahr Umr Formations in a field offshore Abu Dhabi.


  • Customize a mix of field-proven ULTRADRIL high-performance water-base drilling fluid system and POROSEAL copolymeric filtration-control sealing additive.
  • Optimize drilling parameters and improve hole cleaning efficiency by running simulations in VIRTUAL HYDRAULICS drilling fluid simulation software during the planning and execution phase.


  • Successfully drilled the 17 1/2-in interval and ran the 13 3/8-in casing to bottom without any issues related to drilling fluid.
  • Required 1,000 bbl less of the ULTRADRIL system with POROSEAL additive compared with conventional water-base mud (WBM).
  • Encountered no sloughing shale problems, cavings, or mud losses during drilling.
  • Incurred no NPT related to drilling fluid issues.
  • Eliminated the need for backreaming while tripping out of hole and experienced no stuck pipe or bit balling.
  • Completed section in 17 days versus 26 planned days.

Drill long interval through troublesome shale sections

An operator planned to drill the 17 1/2-in interval of its directional well through the Laffan and Nahr Umr Formations offshore Abu Dhabi. The formations include challenging shale sections that exhibit high heterogeneity and lamination, which pose the risks of wellbore breakout and instability. Because of rig limitations and zero-discharge regulations, the use of nonaqueous fluid was not an option.

Integrate fluid, additive, and simulation for customized solution

The ULTRADRIL system was selected because of its previously demonstrated success in the field. The system comprises three primary components designed to deliver excellent inhibition.

  • ULTRAHIB shale inhibitor is a polyamine that inhibits swelling and migration by reducing the tendency of clay to bond with water within an aqueous environment. The inhibitor works by chemically bonding to reactive sites within clay structures, then drawing them tightly together so that water molecules cannot penetrate the spaces between the clay particles.
  • ULTRAFREE ROP-enhancing surfactant coats cuttings and metal surfaces, effectively reducing the sticking tendencies of hydrated solids. This surfactant heads off costly gumbo buildup on bits, BHAs, drillpipe, and casing, minimizing the risk of bit balling as well as helping to increase ROP.
  • ULTRACAP PLUS advanced encapsulating shale inhibitor is a low-molecular-weight, dry acrylic acid copolymer designed to provide cuttings encapsulation and clay dispersion inhibition. The inhibitor adsorbs onto the clay surfaces and forms a protective film that prevents cuttings from sticking to each other or to a shaker screen.

The POROSEAL additive was recommended for its ability to seal microfractures and reduce the risk of shale destabilization. Extensive VIRTUAL HYDRAULICS software simulations were run during planning and execution to optimize drilling parameters and improve hole cleaning efficiency.

For additional wellbore strengthening material, G-SEAL PLUS industrial carbon and graphite bridging agent was also included in the formulation at 6 lbm/bbl. In addition, 15-lbm/bbl calcium carbonate was included to combat potential losses across the suspected faults.

Meet objectives 9 days ahead of plan and without fluid-related NPT

The 17 1/2-in interval was drilled and 13 3/8-in casing was successfully run to bottom without issue. The section was completed in 17 days, which was 9 days sooner than planned. No shale sloughing, cavings, or mud losses were encountered during drilling, and no NPT related to drilling fluid was incurred. Further, backreaming was not required while tripping out of hole, and the casing was run to bottom without stuck pipe, bit balling, or other issues.

Mud weight at TD was 1.32 relative density—less than the planned 1.35 relative density. Additionally, the volume of ULTRADRIL system with POROSEAL additive was 1,000 bbl less than would have been required using conventional WBM. As a result of deploying the G-SEAL PLUS agent and calcium carbonate, no losses were observed across any faults.

Download: Integrated Drilling Fluid System Helps Complete 3,000-ft Shale Interval 9 Days Ahead of Plan  (0.29 MB PDF)

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