Enhanced oil recovery (EOR) techniques can significantly extend global oil reserves once oil prices are high enough to make these techniques economic. Given a broad consensus that we have entered a period of supply constraints, operators can at last plan on the assumption that the oil price is likely to remain relatively high. This, coupled with the realization that new giant fields are becoming increasingly difficult to find, is creating the conditions for extensive deployment of EOR. This paper provides a comprehensive overview of the nature, status and prospects for EOR technologies. It explains why the average oil recovery factor worldwide is only between 20% and 40%, describes the factors that contribute to these low recoveries and indicates which of those factors EOR techniques can affect. The paper then summarizes the breadth of EOR processes, the history of their application and their current status. It introduces two new EOR technologies that are beginning to be deployed and which look set to enter mainstream application. Examples of existing EOR projects in the mature oil province of the North Sea are discussed. It concludes by summarizing the future opportunities for the development and deployment of EOR.

For over 10 years research has been carried out on the impact of low salinity waterflooding on oil recovery. Data derived from corefloods, single well tests, and log-inject-log tests have shown that injecting low salinity water into an oil reservoir should result in a substantial increase in oil recovery in many cases. The results varied from 2 to 40% increases in waterflood efficiency depending upon the reservoir and composition of the brine.In 2005, a hydraulic unit was converted to inject low salinity brine into an Alaskan reservoir, by switching a single injection pad to low salinity water from high salinity produced water. An injector well and 2 close production wells were selected within a reasonably well constrained area. A surveillance programme was devised which included capturing produced water samples at regular intervals for ion analysis and the capturing of production data.Detailed analysis of the production data, and the chemical composition of the produced water, demonstrated an increase in oil production and provided direct field evidence of the effectiveness of LoSal™ at inter-well scales. Additionally, the response of the reservoir to low salinity water injection was confirmed by single well chemical tracer test.In parallel, laboratory studies have led to mechanistic understanding of LoSal™ in terms of multiple-component ionic exchange (MIE) between adsorbed crude oil components, cations in the insitu brine and clay mineral surfaces. The results clearly show that the enhanced oil production and associated water chemistry response was consistent with the MIE mechanism proposed.The oil production data have been modeled using an in-house developed modification to Landmark's VIP TM reservoir simulation package. An excellent match for the timing of the oil response was obtained which provides a good basis for predicting the result for large scale application of LoSal™ flooding.

The relative wettability of oil and water on solid surfaces is generally governed by a complex competition of molecular interaction forces acting in such three-phase systems. Herein, we experimentally demonstrate how the adsorption of in nature abundant divalent Ca2+ cations to solid-liquid interfaces induces a macroscopic wetting transition from finite contact angles (≈10°) with to near-zero contact angles without divalent cations. We developed a quantitative model based on DLVO theory to demonstrate that this transition, which is observed on model clay surfaces, mica, but not on silica surfaces nor for monovalent K+ and Na+ cations is driven by charge reversal of the solid-liquid interface. Small amounts of a polar hydrocarbon, stearic acid, added to the ambient decane synergistically enhance the effect and lead to water contact angles up to 70° in the presence of Ca2+. Our results imply that it is the removal of divalent cations that makes reservoir rocks more hydrophilic, suggesting a generalizable strategy to control wettability and an explanation for the success of so-called low salinity water flooding, a recent enhanced oil recovery technology.

Present and future accelerators' performances may be limited by the electron cloud (EC) effect. The EC formation and evolution are determined by the wall-surface properties of the accelerator vacuum chamber. We present measurements of the total secondary electron yield (SEY) and the related energy distribution curves of the secondary electrons as a function of incident-electron energy. Particular attention has been paid to the emission process due to very low-energy primary electrons (<20 eV). It is shown that the SEY approaches unity and the reflected electron component is predominant in the limit of zero primary incident electron energy. Motivated by these measurements, we have used state-of-theart EC simulation codes to predict how these results may impact the production of the electron cloud in the Large Hadron Collider, under construction at CERN, and the related surface heat load. DOI: 10.1103/PhysRevLett.93.014801 PACS numbers: 29.27.Bd, 41.75.Lx, 79.20.Hx In 1989 an instability driven by photoelectrons was observed at the National Laboratory for High Energy Physics (KEK) Photon Factory. It was not until 1994 that its origin was correctly identified as due to the formation of an electron cloud (EC) [1,2]. Since then several proton-storage rings [3,4], electron-positron colliders [4], and synchrotron radiation (SR) sources, when operating with positrons, have reported similar beam instabilities which are now understood to be due to a coupling between the beam and an EC. Deleterious effects of the EC include interference with diagnostic devices, coupled-bunch coherent beam instabilities, and single-bunch incoherent effects such as emittance increase. In general, the EC is significant in machines with intense, closely spaced, short, positively charged bunches, and vacuum chambers of relatively small transverse dimensions. In the cases of the B factories PEP-II and KEKB, the EC in the positron rings led to important operational limitations and to an intense search for mitigating mechanisms [4 -6]. An EC related effect is the beam-induced electron multipacting, and it can be explained as follows: a few ''seed'' electrons may be generated by ionization of the residual gas or by photoemission. These electrons are accelerated by the bunch electric field in the direction perpendicular to the beam motion. If the bunch charge and the bunch spacing satisfy a certain condition, the traversal time of the electron across the vacuum chamber equals the time interval between successive bunches, and a resonance condition is established. If, in addition, the effective secondary electron yield (SEY) at the chamber is larger than unity, the electron population grows rapidly in time with successive bunch passages, leading to a high electron cloud density. A closely related phenomenon, called trailing-edge multipacting, has also been observed for a single proton bunch at the Los Alamos Proton-Storage Ring (PSR) when the beam intensity exceeds a certain threshold [7]. It could prove important for the future Spallation Neutron...

The crystal habit of barium sulfate formed by the rapid mixing of Ba2+ and SO:-containing brines at 95°C has been investigated and the effects of coprecipitated K + , Mg2+, Ca2+ and Sr2+ ions, supersaturation ratio and barium-to-sulfate mixing ratio on the crystal morphology studied. The most marked crystal morphological changes were induced by varying the supersaturation and mixing ratios. The foreign ions produced relatively subtle effects. At high supersaturations (within the homogeneous nucleation regime), eightpointed star-like crystals were formed, whilst at low supersaturations, the equilibrium rhombohedra1 crystal form was recovered. All precipitates were single crystals.In the presence of crystal growth modifiers, marked morphological changes could be induced. For example, certain polymers induced the formation of millimetre long bundles of needles at pH x 6 and fractal-like hollow cones at pH x 5. In contrast, a range of phosphonate-based molecules, designed to act as barium sulfate scale inhibitors, produced oblate spheroids and very distorted star-like crystals 1 5-20 times smaller than the unmodified crystals. These particles were found to be porous on the nanometer scale. All the precipitates described were single crystals.We have found that the control and prevention of barium sulfate precipitation by phosphonate-based materials at high Ba2 + concentration and low pH (ca. 4.5) are complicated. In the absence of Ca2+ ions in solution, little or no inhibition occurs and evidence suggests that calcium phosphonate complexes are the active inhibitors. In addition, although the inhibitors may act by the classical mechanism of blocking crystal growth sites, they also act as nucleation promoters. This provides an additional mechanism for scale inhibition involving depletion of scaling ions from solution. As part of this work, using dynamic light scattering, we have for the first time demonstrated the presence of 1-10 nm microcrystallites in fully and partially inhibited barium sulfate scaling systems.Many of the brines found in the oil-bearing strata of offshore reservoirs contain high concentrations of alkaline-earth-metal ions (Ba2+, Ca2+, Sr2+ and Mg2+). During secondary oil recovery, seawater (containing SO:-) is injected into the reservoir to maintain the pressure. When the waters come into contact in the region of the well-bore, a solid precipitate can form which blocks production tubing and which can also cause damage to