Preparation and evaluation of soft preformed particle gels for conformance control in carbonate reservoir.

In this paper, we studied on the nanocomposite preformed particle gels (PPGs) for conformance control in fractured-vuggy carbonated reservoirs. The nanocomposite PPGs were synthesized via free radical polymerization, consist of acrylamide (AM), N-vinylpyrrolidone (NVP). PPGs were evaluated at 130 °C and salinity of 2.2 × 105 mg/L. Swelling ratio (Sw) and storage modulus (G′) were measured as a function of aging time. A three-stage swollen history is discovered by means of fitting the power-law relation of modulus and volume fraction. It is inferred that the deviation is caused by stress relaxation and secondary cross-link, respectively. Experimental results show that increasing the concentration of monomer, cross-linker and clay leads to a higher swelling ratio and lower modulus during the aging term. PPGs with 30 wt% monomers, NVP: AM ratio of 6:4, 0.25 wt% cross-linker and 3.0 wt% clay exhibit optimum properties for conformance control at high temperature reservoirs. The propagation and blocking efficiency of PPGs were evaluated in an ideal fracture model. The match relation of particle size and fracture width was discussed. Industrial PPGs products with various sizes were prepared. Toughness measurements and infrared spectrum (IR) show that the properties of PPGs are stable during the scale up production. Finally, the field application in Tahe oil field is briefly introduced. • A kind of nano composite PPG was investigated for conformance control in high temperature carbonated reservoir. • A three-stage history of PPGs under thermal treatment is proposed by means of fitting the G~φ power law relation. • The matching relation of PPG size and fracture width was discussed by an ideal visual model. [ABSTRACT FROM AUTHOR]