Experimental Study on the Preparation and Properties of a Magnetic-Response Nano-tracer for Fracture Monitoring in Unconventional Reservoirs

In response to the challenges of poor stability and low sensitivity of conventional chemical tracers for fracture monitoring, a magnetic-response nano-tracer (MRNT) was synthesized using nano-ferric oxide and polyvinyl alcohol as the main materials, and triethylamine (THA) as the active tracer component to simultaneously monitor oil production and fracture parameters. The chemical structure, micromorphology and particle size of MRNT were characterized using infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy and laser particle size analyzer. The temperature and salt resistance performance and recyclability of MRNT were investigated experimentally, and the fracture and oil production tracking effects of MRNT were studied using a sand-pack model. The results showed that THA was grafted onto the surface of MRNT via hydrogen bonding, and the MRNT particle size is about 500 nm. The MRNT mass change rate is less than 3% at 25 ~ 95 °C and a salinity of 1000 ~ 45000 mg/L, indicating good temperature and salt resistance. Magnetic adsorption separation of MRNT achieves a recovery rate of over 99%. Monitoring shows that multiple fractures have formed, including major fractures, secondary fractures and micro-fractures. The main channel is narrow and the volume is small. In the sand pack, there is a peak contribution rate of oil production of more than 10% during the initial monitoring period. During the medium-term monitoring, the oil production changes uniformly with time and has a high contribution rate. In the later stage, the contribution rate of oil production decreases to less than 5%, with a minimum of less than 1%. The synthesis and monitoring effects of MRNT provide an experimental and theoretical basis for fracture and oil production monitoring in the field.