Detection of Propping Agents in Fractures Using Magnetic Susceptibility Measurements Enhanced by Magnetic Nanoparticles
Authors: Aderibigbe Aderonke , Cheng Kai , Heidari Zoya , Killough John , Fuss Tihana , Stephens Walter T. 
Published: October 2014

Abstract
Reliable detection of propping agents in fractures has been a challenge for the petroleum industry. Researchers are currently investigating the application of nanoparticles as contrast agents for reservoir characterization and advanced reservoir surveillance. This paper demonstrates the use of nanoparticles as contrast agents mixed with proppants that can enhance signals from borehole geophysical measurements, thereby improving the detection of proppants in hydraulic fractures.
The methods used in this paper study 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, using the superparamagnetic nanoparticles mixed with proppants. Numerical simulations are performed simultaneously to show that the distribution of nanoparticles remain concentrated in hydraulic fractures as is demonstrated in our 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 on nanoparticles in the porous media.
We successfully synthesized paramagnetic nanoparticles with a core/shell structure with size of 60 nm–70 nm. The hysteresis loops obtained from the magnetic measurements demonstrate magnetic stability of the nanoparticles at both surface and reservoir temperatures. The magnetic nanoparticles provided high sensitivity when used as contrast agents in magnetic susceptibility measurements of carbonate and organic shale samples. The relative enhancement of the volume susceptibility depends on the minerals present within the formation, concentration of the nanoparticle solution, and the magnetic composition of the proppants. The results of the numerical simulations confirmed the effectiveness of using nanoparticles as contrast agents in highlight fractures and, hence, the location of the proppants. We have demonstrated in the synthetic examples that the nanoparticle concentration in hydraulic fractures is significantly higher than that in the surrounding porous rock in the case of low permeability formations, suggesting that hydraulic fractures can be clearly differentiated from the surrounding formations. We have thus 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. The prospect of injecting magnetic nanoparticles as contrasting agents along with propping agents during fracture treatment is promising for the accurate monitoring and tracking of propping agent. More developments on this approach will lead to improvement in the determination of the hydraulic-fracture geometry, which is of great value in designing hydraulic fracture treatments.