When constructing deepwater wells, incompatibility between synthetic-based mud (SBM) and Portland cements can lead to poor cementation and loss of cement integrity, which in turn may compromise zonal isolation. An alternative cementitious material based on geopolymers has been developed with improved SBM compatibility for primary and remedial cementing purposes as well as lost circulation control. Geopolymer benefits go beyond mere SBM compatibility: it is in fact possible to solidify non-aqueous fluids such as SBM and oil-based mud (OBM) using geopolymer formulations. This also means that non-aqueous fluids (SBM, OBM) can be disposed of in a cost-effective way, which presents a viable option for environmentally acceptable on-site or off-site disposal of drilling muds and cuttings.
Geopolymer is a type of alkali activated material that forms when an aluminosilicate precursor powder (such as fly ash) is mixed with an alkaline activating solution (such as sodium hydroxide). A novel SBM solidification method was developed by blending varied amounts of geopolymer and SBM. This solidification method was tested with various sources of precursor powders, SBMs and OBMs. The rheology and strength of the geopolymer/SBM blends were measured under downhole conditions.
Strength testing results showed that geopolymer cement lost only 30% of its strength when blended with 10% SBM, while a neat Portland slurry lost 70% strength. Geopolymer/SBM blends containing up to 40% SBM were found to have measurable strength when cured under downhole conditions. By changing the amount of geopolymer and SBM in the slurry, the geopolymer/SBM system can be developed into a lost circulation treatment with low compressive strength, or into a primary cementation material with higher compressive strength.
The geopolymer/SBM blends at different mixing ratios have shown great improvement in rheology of the geopolymer cement, allowing for pumpability of the slurry for well cementation. For instance, 30% SBM blends have downhole rheology profiles that approach those of neat Portland slurries.