- Home
- Conferences
- Conference Proceedings
- Conferences
IOR 1991 - 6th European Symposium on Improved Oil Recovery
- Conference date: 21 May 1991 - 23 May 1991
- Location: Stavanger, Norway
- ISBN: 978-94-6282-133-0
- Published: 21 May 1991
51 - 100 of 100 results
-
-
Pilot tests of biogeotechnology applied to enhance oil recovery
Authors S. S. Belyaev, M. V. Ivanov, A. A. Matz and A. Yu. BorisovThe technology to enhance oil recovery of oil-bearing strata based on the targeted activation of stratal microflora and, first of all, hydrocarbon-oxidizing and methanogenic bacteria, was developed. The first stage of activation involves the aeration of water pumped into a stratum with mineral nitrogen and phosporus salts added
-
-
-
Rheotechnology - A New trend in oil production technology
Authors A. H. Mirzajanzade and I. M. AmetovThe paper presents a review of the major results in the field of the rheotechnological methods for oil production. Also shown are the peculiarities of heavy oil production, abnormal temperatures in particular. The advantages of the, new technology based on monitoring of viscoelastic properties of oil and the applied systems are presented.
-
-
-
A Comparison of reservoir management options for high relief light oil reservoirs
Authors J. D. M. Belgrave and W. R. HovdetadThis paper documents a systematic investigation of gravity stable recovery strategies for light oil reservoirs, using an equation of state compositional simulator on a Cyber 205 supercomputer.
-
-
-
On the aspects of reservoir fluids phase behavior important in design of miscible gas injection processes
By Z. NovosadThe study examines features of oil and injection gas (solvent) phase behaviour that control the mechanism of mass transfer in EOR by miscible gas injection.
-
-
-
Minimum miscibility pressure calculations including effects of three phase equilibria
By M. P. WalshThis work presents the first equation-of-state (EOS) algorithm to compute minimum miscibility pressures (MMP) in hydrocarbon systems exhibiting three-phase (L-L-V) equilibria. Previous efforts have been limited to systems involving only two-phase equilibria. This work is particularly applicable to low-temperature reservoirs since they often exhibit L-L-V phase behavior. A comparison of twoand three-phase algorithrn results shows that the two-phase algorithm may overpredict the MMP in cases where three-phase equilibria is realized. The results of a CO2 - West Texas oil system show that the error by the two-phase algorithm is significant and the three-phase algorithm offered here should be used.
-
-
-
Miscible gas EOR in a partially cooled reservoir
Authors S. T. Lee, P. J. Kisha, D. M. Grist and P. J. BriggsThe effect of cold-water induced reservoir cooling on tertiary gas injection processes is investigated. Numerical and analytical models of fluid and heat flows are employed to analyse the reservoir cooling phenomena. For the conditions studied, the injected water cools a significant volume of the reservoir. The altered formation temperature distribution affects significantly the displacement and sweep efficiencies, from the phasebehaviour point of view. Equation-of-state and compositional simulation approaches are adopted to analyse and quantify this effect. It is shown that a partially cooled hydrocarbon formation. can bring about a significantly larger tertiary oil bank than that without considering the temperature alteration.
-
-
-
Mobility control experience in the Joffre Viking miscible carbon dioxide flood
Authors D. J. Stephenson, A. G. Graham and R. W. LuhningThe first CO2 miscible flood in Canada is located in a field that had been waterflooded to its economic limit and abandoned in 1965. Carbon dioxide alternating water injection commenced in January 1984 and incremental recovery from the initial experimental area has exceeded 20% of original oil- in - place bringing total recovery to over 60%. Although oil recovery has been excellent numerical simulation studies suggest that less than half the formation in this area has been contacted by carbon dioxide.
-
-
-
Gas flooding of the Statfjord reservoir, Statfjord Field
Authors S. A. Haugen and S. HaalandGas has been injected into the Statfjord reservoir in the Statfjord Field for more than ten years. The reservoir is a heterogeneous sandstone reservoir of Jurassic age and is not considered as an ideal candidate for gas injection. The displacement is more gravity stable than originally anticipated, and currently a large gas cap has been established on top of the reservoir. A low residual oil saturation is expected behind the gas front. The gas flood is believed to be a multicontact miscible process. Fluid sampling from the field has shown minor transfer of molecules between the oil and gas phases. An aggressive drainage strategy and frequent well interventions have contributed to a high recovery from the Statfjord reservoir.
-
-
-
Deep diverting gels for very cost effective waterflood control
Authors A. J. P. Fletcher, S. Flew, I. N. Forsdyke, J. C. Morgan, C. Rogers and D. SuttlesPlacement of gels in depth is an effective approach to Improving waterflood sweep efficiency, particularly In layered reservoirs. The process can give significant and timely additional oil compared with the waterflood baseline. It can be low cost, and operationally convenient. There are a number of possible approaches to ensuring gel is formed where needed, and nowhere else. In the present case, advantage is taken of the thermal gradient set up when cold water is injected into a hot reservoir (or aquifer). The position of the cold front can be modelled to at least sufficient accuracy to ensure correct gel placement.
-
-
-
Conformance control gels - Formation by contact with brine
Authors I. E. Whittington and D. G. NaaeNew technology for gel treatments has been developed. The gel is formed when a solution of a water-soluble polymer (hydroxypropylcellulose, HPC) and a surfactant (sodium dodecyl sulfate, SDS) mixes with brine. While conventional gels use a chemical initiator or activator, such as a heavy metal like chromium, to form the gel, the new HPC/SDS gel uses the salinity of the connate brine to initiate the gel formation.
-
-
-
Selective penetration of biopolymer profile-control gels: Experiment and model
Authors M. I. Hoefner, R. V. Seetharam, P. Shu and C. H. PhelpsProfile control treatments using polymer gels can improve waterflood performance by reducing fluid channeling through higher-permeability "thief" zones. The success of such treatments often depends on placing the gel preferentially in the thief interval. Laboratory coreflood data presented in this work clearly shows that certain xanthanbased profile control gels exhibit tbe property of "selective penetration." Selective gels flow preferentially into higher-permeability media and resist penetration into tighter media. These gels could tbereforeeliminate the need for mechanical zone isolation and thus reduce the cost of profile control treattnents significantly.
-
-
-
Effect of CR³+ on the rheology of xanthan formulations in porous media: Before and after gelation
Authors R. S. Seright and F. D. MartinExperiments were performed to probe the rheology of chromium(III)-xanthan gels and gelants in porous media. For a large portion of the time before gelation, the presence of 90-ppm Cr³+ did not significantly affect the rheology of a 3000-ppm xanthan solution in Berea sandstone. After gelation, residual resistance factors were not much greater than those for xanthan solutions without Cr³+. Clay and carbonate minerals in Berea may have inhibited gelation by forcing the reaction to occur near neutral pH rather than at the injection pH of 3.8.
-
-
-
Preparation of a water control polymer treatment at high temperature and salinity conditions
Authors A. Zaitoun, N. Kohler, B. K. Maitin and M. ZettlitzerThe reservoir conditions in the northern Germany oilfield of Ploen-Ost on which RWE DEA is the operator are well-suited for the application of water control polymer technology in production wells. Polymers are expected to improve reservoir conformance around the wellbore and thus to stimulate oil production from the lowest permeability layers while reducing water influx from the highest permeability ones. The high temperature (95°C) and salinity (130 giL TDS) of the reservoir led us to test two new polymers, namely HST and Polysaccharide G, which have a better stability than polyacrylamides. Both polymers can selectively reduce the relative permeability to water of Ploen sandstone cores, with little effect on the relative permeability to oil and can thus be considered as valuablewatercontrol agents. Because of its higher shear resistance and its stronger shear-thinning behavior, Polysaccharide Gis expected to be easier to handle than HST.
-
-
-
New biopolymer for EOR Moscow
Authors L. A. Starukhina, V. V. Deriabin and V. J. TitovA new biopolymer has been produced that can satisfy demands to enhance oil recovery for it has a high viscosity of diluted solutions in formation waters. Biopolymer solutions are stable in a wide range of pH values and temperatures, possess pseudoplastic behaviour and steadiness to thermal degradation at temperatures above 100°C. This biopolymer called simusan is an exopolysaccharide (EPS) produced by Acinetobacter species capable to utilize ethanol as a carbon and energy source. An estimation of chemical and rheological properties, its emulsion activity and filterability of simusan solutions as wen as fermentation broth has been performed. A technique to improve filterability of the simusan fermentation broth has been developed. New compositions on the base of simusan possessing thickenning and gelation properties have been produced and tested in the oil fields.
-
-
-
Restriction of gas coning by polymer/silicate well treatment
Authors I. Lakatos, M. Kristof, S. Tromboczky, M. Bodola, I. Munkacsi and J. Lakatos-SzaboThe laboratory and field studies were focussed on development of a well treatment technology which can be used for restriction of gas coning in te Algyo reservoir. The chemical system is a modified version of an earlier method based on simultaneous gelation of polymers and silicates.
-
-
-
A New approach to pseudofunctions for multiphase flow in stratified porous media
Authors P. Ingøy, R. Gauchet and L. W. LakeConsidering flooding of stratified reservoirs, this paper focus on the case with significant gravity effects. Assuming the fluids are incompressible, we develop a new VerticaI Equilibrium (VE) theory, and introduce pseudo-functions to describe the displacement problem. From the form of the pseudorized equations we conclude that previously proposed analytical methods for assessing flood performance may lead to erroneous results due to incorrect treatment of gravity. We derive travelling wave solutions for the pseudorized problem and compare an example case with numerical simulations. We show that the travelling wave solution can be formulated as a new generalized Dietz solution which accounts for reservoir stratifications and capillary effects. Previously published interface models are obtained in the limit of zero capillary pressure. We derive several results for stationary displacement, and introduce a graphical method for assessing the vertical sweep efficiency under these circumstances.
-
-
-
The effect of fracture permeability distribution on waterflood efficiency in naturally fractured reservoirs
By G. HamonThis paper discusses the influence of the vertical distribution of horizontal fracture penneability on the waterflood efficiency. The first part presents the analysis of weIl test pressure data from a vertical weIl completed in a naturally fractured reservoir. A dual-porosity simulator, based on a finite difference discretization of the formation is used to generate pressure versus shut-in time during a build-up. It is found that nested fracture networks with different spacings and penneabilities may reconcile the pressure response and core observations, Field examples are presented. In the second part of the paper, dual-porosity simulations of a water injection are run. The main thrust of this paper is to point out that a very different watercut performance may be obtained depending on whether the matrix block size is derived from core observation only, weIl test analysis only, or takes into account both sourees of infonnation. Guidelines are provided to take into account the effect of nested fracture networks in coarse grid. waterflood simulations with dual-porosity simulators.
-
-
-
An experimental investigation of waterflooding of gas condensate reservoirs and their subsequent blowdown
Authors G. D. Henderson, A. Danesh and J. M. PedenThe phase and flow behaviour of water, gas and condensate in pores at reservoir conditions have been visually investigated using glass micromodels with realistic pore pattems and geometry. The displacement of hydrocarbons, both above and below the dew point, by the advancing water was studied. The model at residual hydrocarbon saturation was depleted and the remobilisation behaviour of the trapped gascondensate phases was investigated. Preliminary core flooding results obtained at conditions similar to the micromodel tests confirm the observed phenomena.
-
-
-
Waterflooding strategy design using optimal control theory
More LessOne of the main problems that arise when designing the development of an oil or a gas-oil field is to find the distribution of wells and to fix the hydrodynamical conditions on them such that the oil recovery can be maximized.
-
-
-
The Gullfaks Lower Brent waterflood performance
Authors H. M. Anes, O. Haga, R. Instefjord and K. G. JakobsenThis paper summarizes the main experiences within reservoir performance after 4 years (1987-1990) of production from the Etive and Rannoch Formations in the Gullfaks Field.
-
-
-
Lean gas injection in a fractured reservoir: Compared performance of nitrogen and methane injection
Authors B. Thiebot and S. SakthikumarA laboratory technique has been developed to perform. natural gas/oil gravity drainage experiments under reservoir conditions, in one or three dimensions, that is on cores having or not the lateral faces open to flow. As an application to the EKOFISK reservoir, a series of experiments has been performed on outerop cores (limestone, chalk) of various permeabilities and capillary hold-up heights, in order to compare the efficiency of methane or nitrogen injection.
-
-
-
Lean gas injection as means for maximizing the recovery on Eldfisk Field (Norway)
Authors M. Durandeau, S. Sakthikumar and P. PoucleeELDFISK field, located in Block 2/7 of Norwegian offshore 20 km South of EKOFISK field, is producing from fractured chalk formations called EKOFISK,TOR and HOD. The paper presents the successive modelling methodology used from 1982 to estimate its performance under natural depletion as well as improved oil recovery processes as a function of the available field information and the improvement of the simulators.
-
-
-
Improved formulation for gravity segregation in naturally fractured reservoirs
Authors F. V. da Vilva and B. MeyerThis paper proposes improved dual-porosity formulations for gas-oil pseudo-capillary pressure and equilibrium gas saturation. These förmulations take account of the effect of oil reinfiltration. fracture slope and capillary continuity across fractures. For most of the highly fractured reservoirs encountered in the North-Sea and in Middle-Eas,. current numerical simulators may not adequately predict long term performances, due to improper treatment of gravity segregation. even though they are tuned to satisfy early history.
-
-
-
An overview of the lOR projects in Turkey
Authors A. Bayrak and R. Ü. GüvenThis paper presents an overview of the improved oil recovery projects under planning, design or application stages by Turkish Petroleum Corporation (TPAO). These are two field wide inmiscible CO2 injection and a field wide waterflood projects.
-
-
-
Compositional study of gravity stable immiscible nitrogen displacement of a black oil
Authors M. D. Frørup, E. H. Stenby and N. BechGravity stable injection of immiscible Nitrogen into steeply dipping, high permeable reservoirs can recover substantial quantities of oil which are not recoverable by water flooding. Gravity stable gas displacement presents a complicated problem in reservoir engineering.
-
-
-
A Study of recovery mechanisms in a nitrogen diffusion experiment
Authors H. Hu, C. H. Whitson and Y. QiTo understand the peculiar recovery phenomenon in a core nitrogen diffusion experiment, anumerical study has been carried out to investigate various governing forces and their interactions. The mathematical model used to simulate the experiment combines the analytical solution in the fracture (open space) and numerical solutions in the core. The analytical solution of the composition distribution in the fracture includes both molecular diffusion and bulk velocity of the gas stream. The numerical solution in the core includes molecular diffusion, capillary pressure, gravity, and Darcy flow. The fully implicit compositional formulation used in the numerical model is necessary because of the large capillarity and composition effects, and the small pressure gradients in the system.
-
-
-
Diffusion and gravity drainage tests to support the development of a dual porosity simulator
Authors F. E. Suffridge and T. A. RennerThis paper presents the results of seven gravity drainage and diffusion- gravity drainage core tests. Tests were performed on a single 4.99 cm diameter by 243.8 cm long Berea core using laboratory fluids representing a range of capillary to gravity force ratios. The objective was to provide a validation database for the gravity function applied in a dual porosity simulator for use in developing optimum depletion strategies for fractured reservoirs.
-
-
-
Relative permeability hysteresis in micellar flooding
Authors E. Eikje, S. R. Jakobsen, A. Lohne and S. M. SkjævelandThis paper presents two-phase relative permeability curves for drainage and imbibition measured by the displacement method for (1) excess water-microemulsion, and (2) excess oil-microemulsion, The results show that the relative permeability curves are process dependent, even at the low interfacial tension of 0.1 mN/m for microemulsion-water, and 0.005 mN /m for microemulsion-oil.
-
-
-
Three-phase microemulsion relative permeabilities experimental and theoretical considerations
Authors B. A. Kvanvik, A. Skauge, B. Matre and K. KolltveitTwo and three-phase unsteady-state relative permeabilities have been measured on Berea cores, using a brine-microemulsion-oil system with low interfacial tension (IFT).
-
-
-
Investigation of the mechanism of chemical destruction of surfactants applied for EOR
Chemical destruction of nonionic surfactants occurs under the action of elements in catalytic amounts, involved in the reservoir medium. In some oil fields the destruction can be as high as 80% (OΠ-10). Main products resulted from the chemical destruction are alkylphenols, paraffins, residuals of polyoxyethylene fragments followed by interetherification to form sulphide and sulphoxide compounds.
-
-
-
Nonequilibrium adsorption of surfactants onto reservoir cores from the North Sea. The effects of oil and clay minerals
Authors T. Austad, P. A. Bjørkum, T. A. Rolfsvag and K. B. ØysædNonequilibrium adsorption of ethoxylated surfactants, mixtures of sulfonates and nonionic alcohoIs, onto two North Sea reservoir sandstone eores has been studied at reservoir temperature. One of the cores was cleaned prior to the adsorption studies, and the other core contained residual oil saturation, thus maintaining the reservoir wettability. The adsorption was followed by circulating the surfaetant solution through the cores for several months (1700 PV), using synthetic sea water.
-
-
-
On the simultaneous determination of dispersion and nonlinear adsorption parameters from displacement tests by using numerical models and optimization tehcniques
Authors C. A. Grattoni and M. S. BidnerThe simultaneous determination of the dispersion and nonlinear adsorption (Freundlich or Langmuir) parameters is obtained automatically by matching results of numerical models with the breakthrough curve measured during a laboratory displacement test. This matching is performed by applying multivariate optimization techniques to minimize the differences between numerical and experimental results. Numerical solutions are obtained by solving the convection-dispersion-nonlinear adsorption equation by finite differences using the Crank-Nicolson method with iterations to account for nonlinearities.
-
-
-
Irreversible adsorption and dispersion effects in progagation of thin slugs of chemicals
Authors V. M. Entov, I. S. Ginzburg and E. V. TeodorovichThe dynamics of the concentration profile in a thin slug of a chemical propagating along reservoir is investigated theoretically. Combined effects of convection, diffusion and partially irreversible adsorption are accounted for. Exact self-similar solutions are derived which shows that irreversibility of adsorption results in more rapid decrease of concentration maximum in the slug. The possible technological implications are discussed briefly.
-
-
-
Overcoming lateral reservoir heterogenerities via horizontal wells
Authors H. P. Freyss and K. BurgesSedimentary rocks are heterogeneous due to the nature of the depositional process. In a producing oil or gas field, the depositional heterogeneity is aggravated by the unbalanced process of oil or gaswithdrawal through disparate producing vertical wells. Overall, this leads to large pressure and saturation imbalances in the various sections of a field and uneven drainage resulting in lower ultimate hydrocarbon recovery.
-
-
-
Control of inflow performance in a horizontal well
Authors R. Tailby, J. Alvestad and A. HenriquezA flexible and cost-effective control of the inflow performance of horizontal wells by the use of multiple completions inside prepacked screens or perforated liners is presented.
-
-
-
Modelling of pressure drop for threephase flow in horizontal wells
Authors V. Korady, G. Renard and P. LemonnierIn most usual situations, the flow into an horizontal weIl will be turbulent due to high flow rates and is expected to have a large impact on the weIl behaviour and production performance. Therefore, accurate pressure drop calculations are needed for a proper representation of mono and multi-phase flow in the wellbore. This is of great interest when simulating highly permeable oil rims when water or gas coning may occur.
-
-
-
Simulation of vertical oil displacement towards horizontal and multi-hole wells
Authors M. M. Maksimov, L. P. Rybitskaya, M. L. Surguchev and V. P. TabakovWhen different types of horizontal wells became involved in oil field development practice, a problem of numerical simulation of the development processes has arisen.
-
-
-
The important effect of pattern shape upon the performance of horizontal wells
Authors R. M. Butler and R. SuprunowiczDespite statements in the literature which are to the contrary, the productivity of horizontal wells increases, in most practical cases, at a rate which is more than proportional to their length.
-
-
-
Imrpoved oil recovery in the global energy perspective
By P. JacquardThe story of oil in the last 25 years has been a paradoxical one. Around 1970, oil reserves amounted to 550 billion barrels. But in the light of the regular decline in the number of years of reserves, some experts did not hesitate to predict that the age of oil would soon come to an end.
-
-
-
The North Sea petroleum history and experience - "An lOR viewpoint
By F. Al-KasimIt is indeed a pleasure and an honour to be invited to speak to you here today. Allow me therefore to extend my sincere thanks to the organizers of this symposium for availing me of this splendid opportunity.
-
-
-
Improved oil recovery with special emphasis on offshore conditions
Authors T. A. McCracken and P. J. BriggsThe remaining oil reserves in the UKCS and Norwegian North Sea are some 18¹ billion barrels. Figure 1 shows a plot of expected recovery factors from 40 UK and Norwegian North Sea fields. The recovery factors have been arranged in ascending order and plotted versus the cumulative percentage of the total initial oil in place from the 40 fields. It can be seen from Figure 1 that the median recovery factor is 42%. The original oil in place in the North Sea is probably in the range of 70 to 120 billion barrels. This gives a residual oil volume of 40 to 70 billion barrels. We conservatively assume that reserves growth of 5% of oil in place can be attributed to improved reservoir management techniques with a further 5% growth through the application of EOR. This amounts to an Improved Oil Recovery (lOR) target of between 7 and 12 billion barrels from the currently discovered North Sea oilfields. In addition we estimate that there remain some 15 billion barrels of oil yet to be discovered, lOR will also expand this resource. There is tremendous target resource for additional reserves to be generated though lOR technology.
-
-
-
Reservoir characterization
More Lessuncertainties about static (affecting volume) and dynamic (affecting flow) reservoir characteristics and future operational factors (affecting regularity) often combine to yield a significant composite technical uncertainty about a field's production forecast.
-
-
-
A Summary of R&D needs for gas injection processes
By F. J. FayersAs shown in the title slide, gas displacement has three broad areas of application to oil recovery, namely miscible, or "nearly miscible", processes, gravity drainage, and fractured reservoir systems. We have seen papers at th is Conference which come into each of these categories. The technology of gas displacement is becoming mature from some points of view, ahhough there are still many stimulating and difficult research challenges for the future. Gas displacement is now established as a successful and economic method for Improved Oil Recovery in light oil reservoirs, even with oil prices as low as say $18 per barrel. The controlling parameters are oil recovery efficiency, where 5 Mscf/bbl is not an unreasonable net target with gas recycling, and gas price, which needs to be in the range of $1-2 per Mscf. In terms of resource conservation, an advantage of gas displacement is that the injected gas is not all lost, but most of it can be produced later for another purpose.
-
-
-
Status of chemical flooding
By J. R. BraggGood afternoon. First, I would like to thank Odd Skontorp and all of the Organizing Committee for the opportunity to help summarize the status of chemical flooding and per'haps raise some topics for reflection and discussion.
-
-
-
From well data to a complete description of a reservoir using geostatistical methods
Authors R. Eschard, B. Doligez and G. LelochThe use of new coneepts in sedimentological interpretation (stratigraphic sequences, carefully done deseription of the cores...) combined with new tools in geostatistics (variograms, proportion curves...) allows to characterize the size and the frequency of sedimentary bodies and of their internal heterogeneities. The geological interpretations and constraints appear to be crucial prerequisites for the consistency of the method.
-
-
-
A Statistical procedure on analysis of acoustic logs for identifying microfractures in carbonate systems
By P. TerdichIn order to define the dynamical schemes of a reservoir it is necessary to reconstruct its main structural and lithological characteristics and, in carbonate systems, especially the distribution of fracturation pattern.
-
-
-
Commercial polymer injection in the Courtenay Field
Authors A. G. Putz and R. C. RivenqAn industrial oparation of polymer injection has been implemented in the Courtenay field which is a satellite of the Chateaurenard field. A large slug of partially hydrolysed polyacrylamide solution with a viscosity of 21 cPo is being injected to displace a 40 cPo oil.
-
-
-
Three-phase relative permeability model for arbitrary wettability systems
By K. O. TemengAn analytical model is proposed for computing three-phase relative permeability from twophase data. The new model is an extension of the well-known probability model due to Stone. with a normalized wettability index as an interpolating factor. Determination of three-phase residual fluid saturations is also discussed.
-
-
-
On the protection against coning provided by horizontal barriers of limited lateral extent
By S. EkrannThe paper determines critical rates to coning for horizontal and vertical wells shielded by favourably positioned impermeable horizontal barriers of limited lateral extent. Mathernatical techniques mimic those used by previous authors for unshielded coning. The Muskat approximation is employed. It turns out that vertical wells can benefit strongly from the presence of a barrier, as measured by the critical rate, depending on barrier position and radius. With horizontal weIls, however, the the critical rate to coning is decreased, except for very wide barriers.
-
-
-
Alternatives to the salinity gradient for controlling the effects of dispersion in surfactant floods
By J. W. BarkerNumerical simulation is used to review the effects of middle phase mobility on the efficiency of a threephase surfactant flood and the use of a salinity gradient to counter the adverse effects of dispersion (by producing 'self-sharpening' of the surfactent slug). Alternative means of producing self-sharpening behaviour are then investigated. Inclusion of an alcohol in the chemical slug is shown to be a viable alternative to a salinity gradient, provided that the phase behaviour properties of the alcohol are chosen correctly. However, under the assumptions that optimal salinity is independent of surfactant concentration and that surfactant partitions almost wholly into the middle phase when that phase exists, it is not possible to achieve self-sharpening behaviour merely by varying the formulation of the surfactant within the chemical slug.
-