Responsive nanoparticle-stabilized foams for conformance control in high-temperature reservoirs

Abstract

Background. Reservoir-tailored conformance control for the stimulation of heterogeneous reservoirs is one major challenge in EOR, especially to reach high temperatures, for instance, in Iranian fields (>150 °C), as conventional surfactant-stabilized foams are not stable that hot due to thermal decomposition and highlighted accelerated drainage. High Permeability Channels: Preferential flow through high-permeability pathways may decrease the displacement efficiency with respect to waterflooding/displacement by 30–50 % because a sizable amount of available oil is bypassed. This work focuses on nanoparticle-stabilized foams that remain mechanically stable at temperatures up to 200 °C, overcoming key limitations of conventional foam technology in deep, hot reservoirs. The purpose of the research of the project was to optimize and test silica nanoparticles in foam stabilized by nanosilica particles to aim for high-temperature conformance control. The individual goals consisted of the following tasks: (1) To investigate the thermal stability of different nanoparticle groups at 25–200 °C, (2) Obtain rheological data in conditions mimicking those found in a reservoir, (3) Characterize particle mobility reduction and foam propagation in carbonate porous media under high temperature and salinity conditions, and finally, (4) Quantify incremental oil production using coreflood experiments at 150–180 °C.

Methods. Lab studies employed silica and alumina nanoparticles (size 15–30 nm, with a concentration of 0.5–1.0 wt%) dispersed into synthetic brine (35,000 ppm TDS) containing alpha olefin sulfonate surfactant. Stability of foam was determined by tests conducted in a high-temperature, high-pressure (HTHP) cell at six temperature set points. Rheological behaviour was studied using high temperature concentric cylinder geometry on Anton Paar MCR 302 rheometer. Six Berea Core flood experiments were performed (12"x2", 180–650 mD permeability) at 150 °C and 180 °C, after systematic waterflood-foam injection-postflush sequences. Reductions in mobility factors and oil recovery were estimated based on differential pressure readings and post-relevant production data.

Results. Nanoparticle-stabilized foams exhibited outstanding thermal stability with half-lives of 38–54 min at 180 °C vs. 2–9 min for control foams (5–6-fold improvements). The optimum formulation for sensory properties was 0.5–1.0 wt% silica nanoparticles and provided a compromise between performance and cost. Flow tests showed shear-thinning behavior (flow behavior index n=0.62–0.68) and apparent viscosities in the range of 28–43 cP at 180 °C; oil-core flood experiments showed mobility reduction factors of 58–73 that greatly surpassed field application thresholds (MRF > 20). Average incremental oil recovery reached 19.5 % for nanoparticle foams, while control foams yielded only 3.8–5.2 %. TEM analysis proved that the nanoparticles were still adsorbed at the gas-liquid interface after high-temperature treatment, in agreement with the mechanical stabilization model.

Conclusions. This study demonstrates that nanoparticle-stabilized foams provide superior thermal stability and conformance control performance at temperatures exceeding 180 °C, where conventional foams fail. The technology delivers mobility reduction factors of 58–73 and incremental oil recovery of 17–23 % OOIP, representing economically significant improvements. Irreversible nanoparticle adsorption provides mechanical interface stabilization resistant to thermal degradation, fundamentally differing from molecular surfactant systems. Results indicate strong potential for field application in deep, high-temperature reservoirs (>150 °C), potentially unlocking billions of barrels of resources currently inaccessible to conventional EOR technologies. Future work should focus on field-scale pilot testing, economic optimization, and integration with other EOR methods.