چكيده به لاتين
Water shutoff remains a significant challenge in oil extraction, particularly in reservoirs characterized by complex features such as fractures and high-permeability zones. Recently, the application of polymer gels has emerged as an effective strategy to control water production and enhance oil recovery. The integration of nanoparticles within the polymer gel matrix is proposed to adjust their physical and chemical properties, thereby improving their functionality under reservoir conditions. However, certain limitations such as shrinkage in the presence of formation water, low mechanical strength, inadequate thermal resistance in hydrogel structures, and insufficient comprehensive studies in fractured porous environments necessitate further investigation.In this study, silica and alpha-alumina nanoparticles were synthesized via the sol-gel method and characterized using XRD, FTIR, FESEM, and EDS tests. The impact of nanoparticles on SPAM/Cr(III) polymer gel systems was assessed through bottle tests, rheological analysis, thermal resistance evaluation, and morphological studies. Additionally, the effect of salinity on the behavior of both polymer gels and nanocomposite gels was explored in formation waters with salinities of 140,000 mg/L and 231,000 mg/L.
FESEM results revealed that the maximum particle size for silica nanoparticles was 85 nm, and for alpha-alumina, it was 45 nm. Silica nanoparticles significantly enhanced the strength of the polymer gel. Moreover, swelling in formation water was observed up to 1.15% in gels containing silica nanoparticles, while those with alpha-alumina nanoparticles showed an increase in shrinkage up to 3.1%. Thermal resistance tests indicated that silica nanoparticles improved the thermal stability of the gels, whereas alpha-alumina nanoparticles did not affect thermal resistance.To assess the performance of the polymer gels and nanoparticle-enhanced gels in porous media, both a homogeneous quarter five-spot micromodel and a heterogeneous dual-layer micromodel comprising low and high-permeability zones were utilized. The micromodel experiments in both configurations demonstrated that silica nanocomposite gels provided superior blockage in high-permeability and fractured areas compared to standard polymer gels. Oil production rates in the presence of polymer gel, silica nanocomposite gel, and alpha-alumina nanocomposite gel were 55.60%, 57.21%, and 47.26% respectively, in the heterogeneous micromodel, and 62.6%, 68.24%, and 58.3% in the homogeneous micromodel.
Further, flooding experiments were conducted to evaluate the efficiency of the synthesized polymer and nanocomposite gels in naturally fractured and hydraulically fractured carbonate cores from an Iranian reservoir. The results indicated that polymer gels effectively reduced permeability contrast in hydraulically fractured cores. Although the gels demonstrated positive effects in these cores, they caused damage in low-permeability rock formations.
Keywords: Water shutoff, polymer gel, nanocomposite, silica nanoparticles, alpha-alumina nanoparticles, oil recovery, fractured reservoirs, reduction of permeability contrast.
