Improved AMD Nanosheet System to Increase Oil Production Under Harsh Reservoir Conditions

Abstract

Amphiphilic molybdenum disulfide (AMD) nanosheet is a novel flake type Nano material, which is different from the widely used particulate Nano material, for increasing oil production. Most of the current researches and applications of nanosheets were for low temperature and low permeability sandstone reservoirs. This work investigated an improved nanosheet system for permeable carbonates at harsh reservoir conditions. AMD nanosheet sample was a concentrated black liquid with flake size about 80*60*1.2 nm. The features in a high salinity water (HSW) and high temperature were characterized by compatibility test, interfacial tension (IFT) test, emulsification test, and phase behavior test. The potential for increasing oil production was evaluated by micromodel displacement tests. The micromodel was treated to oil-wet to simulate the wettability of carbonates. The performances of initial sample and improved sample by a cationic surfactant were compared. Initial AMD nanosheet sample was not compatible with HSW at 95 °C. A cationic surfactant significantly improve the compatibility. IFT of 50 mg/L nanosheet with a light oil was 0.46 mN/m at 25 °C. IFT of The improved system with the surfactant decreased to 0.21 mN/m at 90 °C. The increase of nanosheet and surfactant concentration resulted in an IFT increase. Although IFT was not ultra-low, nanosheet had strong interfacial activity on oil-water interface even at low concentration. Nanosheet-only produced much stable emulsion than surfactant-only. Mixing nanosheet and surfactant increased emulsion stability slightly. Phase behavior results demonstrated that surfactant improved the hydrophilic and lipophilic balance of nanosheet to produce Winsor III type microemulsion. In core flow testing, the nanosheet alone injection partially plugged the core plug with relatively high adsorption/retention. Adding the surfactant improved the migration and reduced adsorption of nanosheet in porous media. Micromodel displacement test showed that improved nanosheet system at low concentration of 50 mg/L increased oil production by more than 20% after water flooding at both ambient temperature and reservoir temperature at 95 °C. This study investigated a more efficient material with same dimension as oil-water interface compared with surfactant or particulate Nano materials. An improved nanosheet system was developed for carbonate reservoirs under harsh conditions.