Wellbore strengthening material blends

Schlumberger Oilfield Services

OPTISEAL wellbore strengthening material (WSM) blend plugs fracture apertures up to 1,200 um while providing fluid-loss control in moderate- to high-permeability formations.

Laboratory testing has confirmed the blend's fracture sealing and fluid-loss-control performance.

Typical Physical Properties
Physical appearance White to gray or tan
Specific gravity 1.6–2.8
Solubility in water at 68 degF [20 degC] Insoluble
Nominal median particle size (d50) 500–600 um


All four blends are designed for loss zones with maximum openings of at least 1,200 um and can effectively reduce the potential for differential sticking, lost circulation and torque and drag through improved sealing of problem zones.

Graphitic material Graphitic material Graphitic material Sized marble
Ground nut shells Sized marble Sized marble and cellulosic material

OPTISEAL treatments can be applied to stop losses using squeeze treatments or spot applications. To prevent losses, OPTISEAL blend can be added continuously to the circulating drilling fluid or through regular, repetitive sweeps. The former constitutes the majority of cases where lost circulation has occurred; the latter can be deployed when drilling through a formation with a known history of losses.

Remedial lost circulation treatments. The basis of design for the treatment is a low-fluid- loss WSM formulation. The blends can be slurrified at the rigsite from sacks or big bags. An alternative is to premix the WSM at a liquid mud plant in a high-volume, high-density slurry before shipping to a rig. The WSM slurry uses the same base fluid as the drilling fluid but is unweighted. The slurry provides greater flexibility, improved logistics, and reduced hazards associated with sacked materials. Typical final concentrations range from 30 to 70 lbm/bbl [85 to 200 kg/m3] depending on severity of losses.

Preventive treatments. The basis of design for the treatment is continuous particle addition to the circulating drilling fluid when drilling a formation known to have losses. The main challenge is to maintain a required PSD and concentration in the drilling fluid. This may be measured at the rigsite using wet sieve analysis or laser reflectance. Typical concentrations range from 12 to 20 lbm/bbl [35 to 57 kg/m3]. The method of treatment will depend on the length of interval to be drilled.

  • Short intervals: The WSM is added to the active pit or spotted at the bit. When drilling ahead, the shaker screens are either bypassed entirely or all but the top screens are removed. This allows the WSM to be directly recycled and retained in the drilling fluid.
  • Extended intervals: Use an MD-3 triple-deck shale shaker to recover the WSM. By managing the particles in circulation, the rheology of the fluid is more easily controlled, resulting in improved ESD management.

Toxicity and handling

Bioassay information is available upon request. Handle as an industrial chemical, wearing protective equipment and observing the precautions described in the safety data sheet.

Packaging and storage

The OPTISEAL blends are packaged in 55-lbm [25-kg] multiwall paper sacks. Store in a dry, well-ventilated area. Keep container closed. Store away from incompatibles. Follow safe warehousing practices regarding palletizing, banding, shrink-wrapping, and stacking.