Application of magnetic nanoparticles mixed with propping agents in enhancing near-wellbore fracture detection

Abstract

Reliable evaluation of proppant placement in hydraulic fractures is challenging because there are environmental and regulatory concerns about existing techniques which use radioactive tracers. Recent research investigations have shown the potential for the application of nanoparticles as contrast agents for reservoir characterization and advanced reservoir surveillance. This paper demonstrates a new technique for using nanoparticles as contrast agents mixed with proppants that can enhance borehole geophysical measurements, such as magnetic susceptibility, thereby improving the near-wellbore detection of proppants in hydraulic fractures. The methods used in this paper include both laboratory experiments and numerical simulations. The experimental approach consists of (a) synthesizing paramagnetic nanoparticles and (b) carrying out a series of magnetic susceptibility core logging measurements, in the presence of the superparamagnetic nanoparticles (i.e., with a core/shell structure with size of 60–70 nm) mixed with proppants. Numerical simulations are performed simultaneously to confirm that the nanoparticles remain concentrated in hydraulic fractures as is demonstrated in the experimental work. We developed a two-phase flow model to investigate the spatial distribution of nanoparticles when they are injected into a hydraulically fractured porous media, in which the hydraulic fractures are filled with propping agents. Furthermore, we used numerical simulations to investigate the effects of heterogeneity as well as rock and fracture properties on spatial distribution of nanoparticles in the porous media. The results of laboratory experiments showed that the relative enhancement of the volume susceptibility of the fractured zones depend on factors such as the type of proppants (e.g., magnetic versus non-magnetic proppants), the concentration of nanoparticles in the injected solution, and the volume of nanoparticle solution and proppants. The use of magnetic nanoparticles lead to a significant enhancement in the detection of fractures, even with widths as small as 0.3 cm. The numerical simulations on synthetic examples show that the nanoparticle concentration in hydraulic fractures is significantly higher than that in the surrounding porous rock in the case of tight formations. We have then illustrated from the experimental and numerical methods that the superparamagnetic nanoparticles, which are mainly concentrated in the fractures can be used as contrast agents mixed with the proppants to highlight the fractures and detect the location of proppants. This detection technique can be applied in the field by using the borehole magnetic susceptibility tools for pre-fracturing and post-fracturing measurements in open-hole wells.