Abstract
Water flooding is crucial means to improve oil recovery after primary production. However, the utilization ratio of injected water is often seriously affected by heterogeneities in the reservoir. Identification of the location of the displacement fronts and the associated reservoir heterogeneity is important for the management and improvement of water flooding. In recent years, ferrofluids have generated much interest from the oil industry owning to its unique properties. First, saturation of ferrofluids alters the magnetic permeability of the porous medium, which means that the presence of ferrofluids should produce magnetic anomalies in an externally imposed magnetic field or the local geomagnetic field. Second, with a strong external magnetic field, ferrofluids can be guided into regions that were bypassed and with high residual oil saturation. In view of these properties, a potential dual-application of ferrofluid as both a tracer to locate the displacement front and a displacing fluid to improve recovery in a heterogeneous reservoir is examined in this paper. Throughout the injection process, the magnetic field generated by electromagnets and altered by the distribution of ferrofluids was calculated dynamically by applying a finite element method, and a finite volume method was used to solve the multiphase flow. Numerical simulation results indicate that the displacement fronts in reservoirs can indeed be detected, through which the major features of reservoir heterogeneity can be inferred. After the locations of the displacement fronts and reservoir heterogeneities are identified, strong magnetic fields were applied to direct ferrofluids into poorly swept regions and the efficiency of the flooding was significantly improved.
Highlights
Ferrofluids are stable colloids composed of small nano-scale solid, magnetic particles coated with a molecular layer of dispersant and suspended in a liquid carrier (Rosensweig, 1997)
Moridis, and Oldenburg et al investigated the flow behavior of ferrofluid in porous media, the results showed that the effect of an external magnetic field on the flow of a ferrofluid in porous media is equivalent to the imposition of a magnetic body force, which means the flow of ferrofluids can be guided (Moridis et al, 1998; Oldenburg and Moridis, 1998; Borglin et al, 2000; Oldenburg et al, 2000)
In regions occupied by a ferrofluid, the magnetic solid particles in the ferrofluid become polarized with the imposition of an external magnetic field, and the ferrofluid is said to be “magnetized.” In this paper, we considered a water-based ferrofluid Hinano-FFW provided by a nanomaterials company in China
Summary
Ferrofluids are stable colloids composed of small nano-scale solid, magnetic particles coated with a molecular layer of dispersant and suspended in a liquid carrier (Rosensweig, 1997). The presence of ferrofluids should produce anomalies in the magnetic field because these fluids alter the magnetic permeability. Such anomalies, in principle, can be detected by magnetic anomaly detectors. In principle, can be detected by magnetic anomaly detectors Based on this feature, Sengupta (Sengupta, 2012) proposed an innovative approach to determining the fracture length and width by injecting ferrofluids into the fracture. When applying an external magnetic field, the ferrofluids in the fracture shall generate a secondary magnetic field which will have a definite phase difference from the original magnetic field. Rahmani et al used a ferrofluid slug to track the movement of a flooding front and studied reservoir permeability heterogeneity (Rahmani et al, 2014; Rahmani et al, 2015)
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