Nano-sized Particles For EOR
- Tormod Skauge (CIPR Unifob) | Kristine Spildo (Ctr for Integrated Petr Research) | Arne Skauge (Ctr for Integrated Petr Research)
- Document ID
- Society of Petroleum Engineers
- SPE Improved Oil Recovery Symposium, 24-28 April, Tulsa, Oklahoma, USA
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
- 4.3.4 Scale, 5.1.1 Exploration, Development, Structural Geology, 1.6.9 Coring, Fishing, 5.4.1 Waterflooding, 1.4.3 Fines Migration, 6.3.7 Safety Risk Management, 5.6.1 Open hole/cased hole log analysis, 4.1.2 Separation and Treating, 5.1 Reservoir Characterisation, 4.1.5 Processing Equipment, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 5.4.10 Microbial Methods, 5.3.2 Multiphase Flow, 1.8 Formation Damage
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During the last decades colloidal dispersion gels (CDG) have been applied as an EOR method, providing sweep improvement in reservoirs with unfavourable mobility ratio. In addition, our core flood results indicate also an improved microscopic sweep or microscopic diversion by nano-size CDG. This paper investigates the oil mobilization properties of nano-sized silica particles and discusses the underlying mechanism of microscopic flow diversion.
Improved microscopic displacement efficiency has traditionally been coupled to changes in capillary number. However, this approach is insufficient to describe processes like low salinity injection, colloid dispersion gels, and microbial enhanced oil recovery.
The paper presents a new concept of EOR by improved microscopic displacement defined as microscopic diversion. This method involves pore blocking and diversion of injection fluids. Multi-phase flow experiments using nano-size silica particles attempts to investigate the effect nano-size (inelastic) fines migration can have on oil mobilization by microscopic diversion.
The oil mobilization properties were investigated by core floods using well-defined nano-sized silica particles in comparison with polymer flood and the combination of polymer and silica particles. Core floods were performed on water-wet Berea sandstone with permeabilities of approx. 500 mD. Filter tests were performed both for selection of suitable silica particles for core flooding experiments. The comparison of hard-sphere silica particles and polymer solution allowed an evaluation of the importance of viscoelastic properties for microscopic diversion.
Successful field applications involving CDGs, all aiming at sweep improvement in adverse mobility heterogeneous oil reservoirs, have been reported by Mack and Smith (1994). They concluded that in most cases, oil production increased and water oil mobility ratio decreased. Based on the result, they also concluded that "colloidal dispersion gels provide an excellent tool for in-depth control of permeability??. Norman et al. (1999) evaluated the economics of CDG flooding and assessed the viability of such injection scheme in low oil prices. More recently there have been several reports of CDG field trials (see e.g. Chang et al., 2006) and Diaz et al., 2008). Both Chang et al. and Diaz and co-workers report an increase in oil production. Chang et al. (2006), described the pilot as being "very successful??, with an additional oil recovery of 10.5% OOIP.
There are little systematic studies of the detailed mechanisms of the CDG process. Most studies have focused on propagation of CDG in porous medium as well as the gelation process. The gelation behaviour of colloidal dispersion gel system was studied by Ranganathan et al. (1998) and Rocha et al. (1989) with the aim of understanding the performance of CDG with respect to in-depth permeability modification. Later, Dong et al. (1998) carried out an extensive displacement tests, and studied CDG structure and rheology using Atomic Force Microscopy (AFM) and dynamic rheological methods. In addition, they reported field results showing good injectivity and additional oil production.
Recently, core flood results that report improved microscopic displacement by use of pregenerated colloid dispersion gels (CDG) have been published (Spildo et al., 2009). The experiments were performed on fresh state reservoir cores and reported average increase in oil recovery of 40 %. The distinction of objective and properties between the conventional approach from the 1980'ies, targeting mainly macroscopic sweep improvement, and the more recent approach using pregenerated colloid particles has defined two classes of CDG. In our studies, and in the work published by Aarra et al. (2005), Bjørsvik et al (2008), Bjørsvik (2008), and Spildo et al. (2009), we use pregenerated colloid particles that are in the range of about 100 nm. These solutions have also been called linked polymer solutions (LPS), and aim at improving the microscopic displacement efficiency in addition to the macroscopic sweep.
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