This invention has applications for a variety of surveying and mapping activities in the petroleum industry.
Nanoreporters are a class of nanoparticles containing a solid core material which is released in the presence of oil. They are used in the petroleum industry for hydrocarbon discovery. An aqueous suspension of nanoreporters is injected into the subsurface before being recovered and analyzed for released core material.
Existing nanoreporters rely on polyelectrolytes attached to their surfaces to keep them suspended in the aqueous medium. However, these polyelectrolytes are poorly solvated at high salinity and are susceptible to breakdown at elevated temperatures, compromising the colloidal stability of existing nanoreporters under conditions commonly encountered in oil reservoirs.
This invention provides a class of nanoreporter particles stabilized by surface-bound polyampholytes. Polyampholytes are ionic polymers containing both anionic and cationic groups, unlike polyelectrolytes which contain either one or the other. This diversity of ionizable groups allows polyampholytes to maintain some degree of charge across a wide range of salinity and pH. When dispersed in water, the like-charged polyampholyte-coated nanoreporters electrostatically repel one another and resist aggregation, thereby stabilizing the suspension.
In tests using both synthetic and natural reservoir brines, the novel nanoparticles described in this invention have achieved long-term colloidal stability at salinities as high as 120,000 mg/dm3 and temperatures as high as 90 ℃ -- roughly twice the stability limit previously achieved.
- Resistant to thermal decomposition
- Maintains colloidal stability over a wide range of salinity and pH
- Compatible with wide variety of payloads for diverse mapping and exploration applications