A model study of enhanced oil recovery by flooding with aqueous surfactant solution and comparison with theory

With the aim of elucidating the details of enhanced oil recovery by surfactant solution flooding, we have determined the detailed behavior of model systems consisting of a packed column of calcium carbonate particles as the porous rock, n-decane as the trapped oil, and aqueous solutions of the anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT). The AOT concentration was varied from zero to above the critical aggregation concentration (cac). The salt content of the aqueous solutions was varied to give systems of widely different, post-cac oil–water interfacial tensions. The systems were characterized in detail by measuring the permeability behavior of the packed columns, the adsorption isotherms of AOT from the water to the oil–water interface and to the water–calcium carbonate interface, and oil–water–calcium carbonate contact angles. Measurements of the percent oil recovery by pumping surfactant solutions into calcium carbonate-packed columns initially filled with oil were analyzed in terms of the characterization results. We show that the measured contact angles as a function of AOT concentration are in reasonable agreement with those calculated from values of the surface energy of the calcium carbonate–air surface plus the measured adsorption isotherms. Surfactant adsorption onto the calcium carbonate–water interface causes depletion of its aqueous-phase concentration, and we derive equations which enable the concentration of nonadsorbed surfactant within the packed column to be estimated from measured parameters. The percent oil recovery as a function of the surfactant concentration is determined solely by the oil–water–calcium carbonate contact angle for nonadsorbed surfactant concentrations less than the cac. For surfactant concentrations greater than the cac, additional oil removal occurs by a combination of solubilization and emulsification plus oil mobilization due to the low oil–water interfacial tension and a pumping pressure increase

Enhanced oil recovery by flooding with aqueous surfactant solution : a model study and comparison with theory

The aim of the work within this thesis is to elucidate the details of enhanced oil recovery by surfactant solution flooding. This was achieved by determining the detailed surface chemistry and flow behaviour of model systems consisting of a packed column of calcium carbonate particles as the porous rock with interstices filled with a pure oil, and aqueous solutions of three different surfactants (an anionic, cationic and nonionic) as the displacing phase. Each three phase system is characterised in detail in terms of its surface chemistry properties, including; water-rock adsorption, water-oil interfacial tensions, water-oil-rock contact angles, aqueous phase behaviour, microemulsion phase behaviour and water-oil partitioning.Two models are derived to enable modelling of the oil recovery performance of the aqueous surfactant solutions being pumped through the powder packed columns with interstices filled with the oil. The first model enables the concentration of free surfactant, [surf]free, present within the packed columns during flooding to be calculated from the initial concentration pumped in, [surf]init. This allows a direct comparison between surface chemistry characterisation results (which relate to [surf]free) and %oil recovery results (which relate to [surf]init). The second two-part model shows how, based on the hypothesis that the residual oil is trapped in the form of liquid bridges between contacting calcite particles, the measured %oil recovery variation with surfactant concentration can be understood and predicted for concentrations of surfactant both below and above the cμc in terms of the characterisation results.It was found that, for surfactant concentrations cμc, additional oil is recovered by a solubilisation plus emulsification mechanism. Experimental results were in reasonable agreement with those predicted from the model

Model Study of Enhanced Oil Recovery by Flooding with Aqueous Solutions of Different Surfactants: How the Surface Chemical Properties of the Surfactants Relate to the Amount of Oil Recovered

© 2016 American Chemical Society. The main aim of this work is to establish how the fraction of oil recovered from an oil-filled calcite powder packed column by injection of aqueous surfactant solution depends on the phase behavior and surface chemical properties of the surfactant system. We have measured the phase behavior, the adsorption of surfactant to the oil-water, calcite-water, and calcite-oil interfaces, tensions, and contact angles for anionic, cationic, and nonionic surfactant/oil/aqueous phase systems. We show how the measured surface chemical properties can be used to approximately predict the fraction of oil recovered as a function of the volume and concentration of the surfactant solutions injected into the column. Measured and calculated plots of %oil recovery versus surfactant concentration show reasonably good agreement for the different surfactant systems. The experimentally validated model for oil recovery provides a sound basis for the rational selection of surfactant type and concentration to achieve maximum oil recovery based on laboratory measurements of the surface chemical properties of candidate surfactants

Why compensating fibre nonlinearity will never meet capacity demands

Current research efforts are focussed on overcoming the apparent limits of communication in single mode optical fibre resulting from distortion due to fibre nonlinearity. It has been experimentally demonstrated that this Kerr nonlinearity limit is not a fundamental limit; thus it is pertinent to review where the fundamental limits of optical communications lie, and direct future research on this basis. This paper details recently presented results. The work herein briefly reviews the intrinsic limits of optical communication over standard single mode optical fibre (SMF), and shows that the empirical limits of silica fibre power handling and transceiver design both introduce a practical upper bound to the capacity of communication using SMF, on the order of 1 Pbit/s. Transmission rates exceeding 1 Pbit/s are shown to be possible, however, with currently available optical fibres, attempts to transmit beyond this rate by simply increasing optical power will lead to an asymptotically zero fractional increase in capacity

The benefit of split nonlinearity compensation for single-channel optical fiber communications

In this Letter we analyze the benefit of digital compensation of fiber nonlinearity, where the digital signal processing is divided between the transmitter and receiver. The application of the Gaussian noise model indicates that, where there are two or more spans, it is always beneficial to split the nonlinearity compensation. The theory is verified via numerical simulations, investigating transmission of single channel 50 GBd polarization division multiplexed 256-ary quadrature amplitude modulation over 100 km standard single mode fiber spans, using lumped amplification. For this case, the additional increase in mutual information achieved over transmitter- or receiver-side nonlinearity compensation is approximately 1 bit for distances greater than 2000 km. Further, it is shown, theoretically, that the SNR gain for long distances and high bandwidth transmission is 1.5 dB versus transmitter- or receiver-based nonlinearity compensation

Network equipment and their procurement strategy for high capacity elastic optical networks

© 2016 Optical Society of America. In elastic optical networks, the success of providing high network capacity depends on the optical signal-to-noise ratio (OSNR) values of network lightpaths. As each lightpaths OSNR value defines the modulation format and capacity it can support, having high OSNRlightpaths is always beneficial. Hence, with a given set of modulation formats, service providers need to optimize their optical infrastructure, including in-line amplifiers and reconfigurable optical add-drop multiplexers (ROADMs), given the size and topology of their core networks. This also will have a direct impact on vendors who need strong insight into the requirements of service providers and their networks in terms of equipment and new technology. Therefore, in this paper a comprehensive model based on the local optimization which leads to a global network optimization (LOGON) strategy of the Gaussian noise (GN) model has been proposed, which helps in estimating the lightpath OSNR and clearly quantifies the noise contributions from in-line amplifiers and post-amplification at the ROADMs. The model introduces closed-form expressions to calculate nonlinear impairment (NLI) contributions for various span lengths while using either erbium-doped fiber amplifiers (EDFAs) or H-Raman amplifiers, which helps in optimizing the signal launch power to achieve maximum link OSNR. In addition to this, an offline strategy has been proposed that can help service providers to optimize their procurement of network equipment upfront and give insight into how much of the capacity bottleneck is alleviated in their networks if they do this. To demonstrate all of the above, the UK, Pan-European, and US Core networks have been considered, which illustrate differences in link lengths and reduced node density. It is seen that improving the OSNR conditions at the ROADM increases the network capacity when noise from in-line amplifiers is significantly reduced. Among the three networks, we found that the UK network responded the most to improved OSNR conditions at the ROADM nodes due to small link lengths and less line noise. Among the amplifiers, we found that improving ROADMs while having H-Raman in the links resulted in a maximum capacity increase. For the UK network at FG=12.5 GHz, the capacity increases by 6650 Gbps, while for the larger Pan-European and US networks, the capacity increase reduces to 4550 and 1600 Gbps due to increased link lengths and line noise. Further, following the offline strategy, we are able to accommodate 1737, 1481, and 615 100G demands using H-Raman for the UK, Pan-EU, and US networks at FG=12.5 GHz until 10%blocking is reached. Thereby, H-Raman provides 7.5%, 35.8%, and 94.9%extra capacity, respectively, for the UK, Pan-EU, and US. Finally, using H-Raman, all lightpaths in the UK network operate at PM-64QAM with maximum capacity at the end of the procedure.INSIGHT - EP/L026155/

Comparison of low complexity coherent receivers for UDWDM-PONs (λ-to-the-User)

It is predicted that demand in future optical access networks will reach multigigabit/s per user. However, the limited performance of the direct detection receiver technology currently used in the optical network units at the customers' premises restricts data rates per user. Therefore, the concept of coherent-enabled access networks has attracted attention in recent years, as this technology offers high receiver sensitivity, inherent frequency selectivity, and linear field detection enabling the full compensation of linear channel impairments. However, the complexity of conventional (dual-polarization digital) coherent receivers has so far prevented their introduction into access networks. Thus, to exploit the benefits of coherent technology in access networks, low complexity coherent receivers, suitable for implementation in ONUs, are needed. In this paper, the recently proposed low complexity coherent (i.e., polarization-independent Alamouti-coding heterodyne) receiver is, for the first time, compared in terms of its minimum receiver sensitivity with five previously reported receiver designs, including a detailed discussion on their advantages and limitations. It is shown that, of all the configurations considered, the Alamouti-coding based receiver approach allows the lowest number of photons per bit (PPB) transmitted (with a lower bound of 15.5 PPB in an ideal implementation of the system), while requiring the lowest optical receiver hardware complexity (in terms of the optical component count). It also exhibits comparable complexity to the currently deployed direct-detection receivers, which typically require over 1000 PPB. Finally, a comparison of experimentally achieved receiver sensitivities and transmission distances using these receivers is presented. The highest spectral efficiency and longest transmission distance at the highest bit rate (10 Gb/s) was reported using the Alamouti-coding receiver, which is also the only one, to date, to have been demonstrated in a full system bidirectional transmission

Real time 100 Gbit/s electrical Nyquist WDM transmitter

We demonstrate the use of passive electrical filters to produce high quality spectrally-shaped 29 Gbaud WDM signals with a 20 dB bandwidth of 32 GHz, a roll-off of 4.8 dB/GHz and a required OSNR of 12.1 dB

A Comparison of Impairment Abstractions by Multiple Users of an Installed Fiber Infrastructure

We compare three independent impairment abstractions of an installed fibre infrastructure. Abstractions agreed to within 1.3dB despite being obtained from different nodes using different terminal equipment. Validation using a DWDM virtual topology was within 1.4dB