Optimized Surfactant IFT and Polymer Viscosity for Surfactant-Polymer Flooding in Heterogeneous Formations

Surfactant Polymer flooding (SP flooding) has drawn more attention than Alkaline Surfactant Polymer flooding (ASP flooding) in China due to the difficulty of demulsification and the scale formation problem from the alkali in ASP. Traditionally, the primary requirement for the surfactant in SP flooding is the lowest interfacial tension (IFT). However, core flooding tests performed in a series of heterogeneous models have demonstrated there exist optimized surfactant IFT and polymer viscosity for SP flooding, which can maximize the oil recovery of a heterogeneous formation. The optimized surfactant IFT has a low value but not the lowest possible value, and polymer viscosity is at an appropriately high value, but not the highest possible value. This paper summarizes and analyzes more than 40 core flooding test results and provides possible mechanisms for the results

Enhanced Oil Production Through a Combined Application of Gel Treatment and Surfactant Huff\u27n\u27puff Technology

Surfactant huff-puff for production wells has become a recent interest, especially for extremely heterogeneous reservoirs. However, injected surfactant will preferentially move into fractures in fractured reservoirs or higher permeability zones in unfractured reservoirs and will bypass much of the reservoir. In addition, the surfactant will be produced immediately after the production well resumes to production, so the soaking time is limited. This paper introduces a novel process which couples gel treatment and surfactant huff-puff in one EOR process in which surfactant solution is first injected into the production well, then followed by gel treatment. The proposed method has been applied for 10 production wells in a polymer flooding unit in Daqing oilfield. The best compatible surfactant and gel were screened out for the given reservoir conditions before the field application. The mechanisms of the proposed method were studied using core flooding experiments. The field application design process is presented and the application results have been analyzed. Application results show pressure drawdown test can be an important criterion to select candidate for the combined method

The Property Variations of Produced Polyacrylamide from Polymer Flooding Reservoirs and Their Effects on Concentration Detection

Because the injected polymer (polyacrylamide) often quickly breaks through to production wells during polymer flooding, its concentration detection is very significant. However, due to the variations in the relative molecular mass and the degree of hydrolysis of produced polymer, the conventional detection methods, including the viscosimetry and starch-cadmium iodide colorimetry, are no longer suitable to detect its real concentration. This paper introduced a new detection method-ultrafiltration concentration film\u27s desaturation. By purifying and concentrating the produced polymer solution using an ultrafiltration system, then dehydrating the aqueous and dry up the remains, this method can detect the concentration directly. The said method has been evaluated in the laboratory and compared with the other two conventional detection methods, verifying its adaptability and high exactitude. The produced polymers from three different polymer flooding units have been detected using this novel method. The results show that the produced polymer relative molecular mass decreased greatly but its degree of hydrolysis increased obviously. The reasons and differences have been analyzed. These corresponding variations makes the detected results by the conventional methods be much lower than the actual, meaning that the previous methods need to be improved or replaced

CO2, Water and N2 Injection for Enhanced Oil Recovery with Spatial Arrangement of Fractures in Tight-Oil Reservoirs Using Huff-‘n-puff

Tight oil has been effectively developed thanks to artificial fracture technology. The basic mechanism of effective production through fractures lies in the contact between the fractures (both natural and artificial) and the matrix. In this paper, the natural tight cores from J field in China are used to conduct experimental studies on the different fluid huff-‘n-puff process. A new core-scale fracture lab-simulation method is proposed. Woven metallic wires were attached to the outer surface of the core to create a space between the core holder and core as a high permeable zone, an equivalent fracture. Three different injecting fluids are used, including CO2, N2 and water. The equivalent core scale reservoir numerical models in depletion and huff-n-puff mode are then restored by numerical simulation with the Computer Modeling Group—Compositional & Unconventional Reservoir Simulator (CMG GEM). Simulation cases with eight different fracture patterns are used in the study to understand how fracture mechanistically impact Enhanced Oil Recovery (EOR) in huff n puff mode for the different injected fluids. The results showed: Firstly, regardless of the arrangement of fractures, CO2 has mostly obvious advantages over water and N2 in tight reservoir development in huff-‘n-puff mode. Through EOR mechanism analysis, CO2 is the only fluid that is miscible with oil (even 90% mole fraction CO2 is dissolved in the oil phase), which results in the lowest oil phase viscosity. The CO2 diffusion mechanism is also pronounced in the huff-‘n-puff process. Water may impact on the oil recovery through gravity and the capillary force imbibition effect. N2, cannot recover more crude oil only by elasticity and swelling effects. Secondly, the fracture arrangement in space has the most impact on CO2 huff-‘n-puff, followed by water and finally N2. The fractures primarily supply more efficient and convenient channels and contact relationships. The spatial arrangement of fractures mainly impacts the performance of CO2 through viscosity reduction in the contact between CO2 and crude oil. Similarly, the contact between water in fractures and crude oil in the matrix is also the key to imbibition. In the process of N2 huff-‘n-puff, the elasticity energy is dominant and fracture arrangement in space hardly to improve oil recovery. In addition, when considering anisotropy, water huff-‘n-puff is more sensitive to it, while N2 and CO2 are not. Finally, comparing the relationship between fracture contact area and oil recovery, oil production is insensitive to contact area between fracture and matrix for water and N2 cases

Magnetic properties and high frequency characteristics of isotropic FeCoZr thin films with stripe domains

Magnetic properties and high frequency characteristicsof (Fe70.6Co29.4)100−xZrx (x = 4.0 − 18.2 at.%) thin　films have been investigated. The saturation magnetization　4πMs decreases continuously from 21.7 kGs for x = 4.0 at.%　to 12.2 kGs for x = 18.2 at.% and it is consistent with the　decreasing of Fe-Co composition. It is found that the filmsshow nearly isotropic magnetic behavior in the film plane　for the Zr content ranging from 7.2 to 18.2 at.%. These films　exhibit a weak perpendicular magnetic anisotropy with coercivity　values of 24–67 Oe. Meanwhile, the in-plane isotropic　FeCoZr films show a good high frequency response of permeability.　In particular, the film with x = 7.2 at.% shows a　resonance frequency of 2.8 GHz along the direction perpendicular　to the stripe domain axis. The permeability spectra　of the thin films with higher Zr content display multiple　resonance peaks, which may be due to the perpendicular　magnetic anisotropy induced by the stress