The present paper describes the development of unique chemistries for plugging and sealing water producing zones and binding produced sand in unconsolidated formations. This is achieved by tuning the surface chemistry of the nanoparticles to act as either conformance sealants or as sand binders. Wherein the sealants would completely seal-off the water and gas producing zones, the binders would consolidate the produced sand while maintaining the reservoir permeability.
The sealing and binding mechanisms of the nanoparticles are based upon triggered chemistries to achieve delayed gelling activation to ensure proper placement of the treatment into the target zone and avoid premature plugging of pipe lines, coiled tubing or other tubulars. The treatment can be placed downhole as a single pill. When the surface chemistry is tuned for the nanoparticles to act as binders for sand consolidation, the pill has high affinity to the solid surface and therefore is less prone to build up in the pore space. Once cured at reservoir temperature it forms a thin layer of hard gel around the surface of the sand particles, cementing the sand grains together at the same time maintaining open porosity to ensure easy flow of hydrocarbons and injected water. When the pill is deployed as a sealant for water conformance, it occupies the available pore space to seal-off the water producing zones. The newly developed systems can be effectively applied as sealants or binders up to BHST of 300°F.
The surface modified nanoparticles were studied for their abilities to consolidate loose sand and at the same time maintain good permeability in case of binders, while to plug and seal water producing zones in case of conformance sealants. The static and dynamic gelation times were evaluated up to 300°F. It was shown that the gelation time of the nanoparticles can be controlled by surface chemistry modification, pH alterations as well as by adjusting the concentration of the activator, which is advantageous as it allows the treatment to remain pumpable over predictable periods of time. The effects of shear rate on gelation time and viscosity buildup are presented. Regain permeability studies showed that permeability could be controlled by specific surface modifications of the nanoparticles.
The novelty of this paper is that it not only describes the development of unique nanoparticles for water conformance and sand control, but also provides a selection criteria for applying the surface modified nanoparticles for these downhole applications.