This work aims at evaluating a new surfactant based viscoelastic fluid for Chemical EOR applications. The surfactant based fluid exhibits a viscous phase at low concentration and high temperature, useful for improving oil recovery.The viscoelastic fluid is induced by wormlike micelles formed by self-assembled surfactants. The phase diagram of the surfactant in pure water was established using a pervaporation-based microfluidic device (Leng et al., PRL, 96, 2006). Isotropic wormlike micelles have been observed up to 12 % w/w. In a second step, Particle Tracking Microrheology (PTM) was used to investigate the rheological properties of the fluid for surfactant concentrations below 2% w/w in water. Viscosity at low surfactant concentrations (0.1% to 0.3 % w/w), T= 80°C, in synthetic sea water (3.9 % w/w TDS) and in sodium chloride (2 % w/w TDS) has been recorded. Data shows that the viscosity is weakly dependent on brine concentration and evolves between 3 and 15 mPa.s (γ=10 s -1 ), for surfactant concentrations between respectively 0.1% to 0.3 % w/w.The second series of tests consisted of core-flood experiments at 80°C in Clashach sandstone with brine solution (NaCl 2% w/w) containing surfactant concentrations between 0.1 %w/w and 0.3 %w/w. The surfactant is shown to adsorb moderately on the sandstone (50 μg/g) and displace a great fraction of residual oil (from Sor=0.49 to Sor=0.20).These preliminary results show a strong potential for this new surfactant based viscoelastic fluid in chemical EOR. Compared to other viscoelastic fluids this product shows the following advantages:Superior viscosity, at low surfactant concentration, in hard brine and at high temperature Better displacement of residual oil in core-flood with moderate adsorption
We study the cluster statistics and the viscosity of a two-dimensional suspension of passive macroscopic spheres undergoing shear, The second moment of the finite cluster statistics exhibits a maximum for a 2-D concentration q5 s near 0.67 without measurable anomaly in the viscosity. The results of the cluster statistics are compared to those obtained in percolation.Key words: Suspension, cluster statistics, viscosity, percolation lntroductionIt was suggested by de Gennes [1] that one could try to explain the plug-flow phenomenon in suspensions [2] on the basis of an analogy with percolation. In that analysis, the dynamical clusters induced by hydrodynamical interactions between suspended particles are similar to percolation clusters. Their mean size grows with particle concentration, and one can expect a critical concentration above which an "infinite" cluster appears, a cluster which contains most of the total (finite) number of particles. So, we were led to study macroscopic passive particle suspensions with regard to their rheology (viscosity, velocity profile) as well as to their statistical cluster properties (mean size, number, length). In order to simplify the observation of clusters, we carried out the study on bidimensional suspensions; preliminary results were published elsewhere [3]. Statistical parameters of the suspensionThe suspension is a two-dimensional collection of passive spheres (diameter d = 5 mm) in a layer (thickness t = 5 mm) of a liquid, the density of which is adjusted to that of the spheres. The suspension was studied in laminar steady flow with a low Reynolds number ( R e~0 . 1 ) in a Couette viscometer (inner diameter R1 = 1.7 cm or 3.35 cm, outer diameter R2 = 9.25 cm õr 18 cm). The inner cylinder is fixed by a 911 torsion wire, the outer one rotating with angular speed f~. The 2D-concentration P s of a suspension containing N spheres is defined by d 2 Ps = N 4(R2 _ R{ )and related to the volume concentration qsv by 3 Bs = ~-~v. For 45s between 0 and 0.80, we study the relative viscosity r/r (ratio of the effective viscosity of the suspension to that of the pure liquid) and the statistical grouping of spheres, by counting from photographs of the suspension undergoing the Couette flow the number ns of clusters of s spheres in contact*), the S 2 ---~~s n « -(mass averaged) mean size. s *) Two spheres are said "in contact" when they seem adjoining within the photographic resolution that is in our case about a tenth of a sphere diameter.
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SMG Microgels are pre-gelled polymers having a narrow size distribution and behaving like large polymer molecules whose stability is strongly enhanced by internal crosslinks. The largest species have a size of around 2 μm, which makes them suitable for Water Shutoff and Conformance Control applications in matrix reservoirs. SMG Microgels have been firstly used as water shutoff agents in gas storage wells and showed high efficiency to reduce water production while enhancing gas production. This paper reports a Conformance project which has been recently deployed in a heterogeneous sandstone reservoir. The pilot pattern consisted of one central injector, surrounded by 7 offset producers, with a spacing between 150 and 450 m. Reservoir permeability ranges between 10 and 1,000 mD with an average of 125 mD. Reservoir temperature is 48°C and salinity is 8,000 ppm TDS. Soft SMG with size around 2 μm was chosen regarding reservoir conditions. Microgel size prevented invasion of lowest permeability zones and created flow resistance in highest permeability zones by adsorption on the rock. Microgel slug corresponded to 0.1 Pore Volume and was 10,000 m3. Microgel injection proceeded over a period of 3 months. WHP remained below max pressure authorized of 1,500 psi. Closest producers responded within 3 months after microgel injection, with noticeable increase in oil rate along with a reduction of a few points of water cut. After one year 6 offset producers upon 7 were responding to the treatment. Three producers showed strong increase and sustained oil production, three had low response and one well lost both water and oil, showing diversion to the other wells. The trend remains steadily established in the pattern. After one year, 10,000 bbl of additional oil has been produced, along with a reduction of water production of 125,000 bbl.
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