Foam, a dispersion of gas in liquid, has been investigated as a tool for gas-mobility and conformance control in porous media for a variety of applications since the late 1950s. These applications include enhanced oil recovery, matrix-acidization treatments, gasleakage prevention, as well as contaminated-aquifer remediation. To understand the complex physics of foam in porous media and to implement foam processes in a more-controllable way, various foam-modeling techniques were developed in the past 3 decades.This paper reviews modeling approaches obtained from different publications for describing foam flow through porous media. Specifically, we tabulate models on the basis of their respective characteristics, including implicit-texture as well as mechanistic population-balance foam models. In various population-balance models, how foam texture is obtained and how gas mobility is altered as a function of foam texture, among other variables, are presented and compared. It is generally understood that both the gas relative permeability and viscosity vary in the reduction of gas mobility through foam generation in porous media. However, because the two parameters appear together in the Darcy equation, different approaches were taken to alter the mobility in the various models: only reduction of gas relative permeability, increasing of effective gas viscosity, or a combination of both. The applicability and limitations of each approach are discussed. How various foam-generation mechanisms play a role in the foam-generation function in mechanistic models is also discussed in this review, which is indispensable to reconcile the findings from different publications. In addition, other foam-modeling methods, such as the approaches that use fractional-flow theory and those that use percolation theory, are also reviewed in this work. Several challenges for foam modeling, including model selection and enhancement, fitting parameters to data, modeling oil effect on foam behavior, and scaling up of foam models, are also discussed at the end of this paper.

Whereas on-shore polymer injection may be qualified as a mature EOR technique, considering the hundreds of operations that have been conducted all over the world, only one polymer pilot has been implemented offshore, and none in deep offshore conditions. A very thorough feasibility study of polymer injection has been made on the Dalia field in Angola, a typical deep-offshore high permeability (>1D as an average) sandstone reservoir containing medium viscosity oil (3 to 7cP under reservoir conditions). The study has demonstrated that high molecular weight hydrolyzed polyacrylamides could be used under a wide range of salinities covering sea water and a mixture of sea water and produced water. Additional recoveries in the range of 3 to 7 % can be expected in this particular context of large well-spacing development of a medium viscosity field. Powder polymer supply is achievable for deep offshore fields either with a specific bulk carrier or using standard international containers to transport big bags (750 kg). Although the on-deck option is simpler, even in the case where no room is left on the existing FPSO, marine options can be found to safely process the polymer on a barge connected to the FPSO (depending on the sea conditions), but the on-deck option is more simple. The need for an injectivity pilot is compulsory to demonstrate the operability of the facilities, and the injectivity of the polymer solution. A single well test has been designed and is planned fall 2008 in Luanda on one of the well of the Camelia reservoir. A skid dedicated to the injectivity test has been designed, assembled and constructed to prepare a mother solution of polymer from powder. Tested in France (no injection), the skid has been shipped to Luanda for installation on the FPSO during summer 2008. Future of the project will depend on the injectivity tests results and on-going studies on a phased approach. Introduction Deep offshore reservoirs may be good candidates for EOR by polymer injection :they are generally shallow (below sea floor), which means rather low temperature;waterflooding is the preferred basic recovery mechanism, for pressure maintenance and sweeping;very often, the reservoir oil is rather viscous, as a result of biodegradation which has occurred due to temperature conditions; recovery by water injection is then adversely affected by an unfavourable mobility ratio, and can be improved by injecting viscosified water;the reservoirs are often turbidites of very good characteristics, allowing an efficient propagation of high molecular weight polymers;the wells are quite prolific, for both production and injection; injecting a viscous solution should not be an issue. Despite this long list of positive criteria there is still no implementation of polymer injection in deep offshore conditions and only two small off shore pilot operation [1–2] whereas on-shore polymer injection may be qualified as a mature EOR technique, when considering the hundreds of operations that have been conducted all over the world. Several key issues have to be faced in deep offshore, that are a major step out versus existing commercial onshore projects: the range of salinities to be met over field life, particularly if sea water is to be injected (most existing - on shore- projects are injecting almost fresh water)the larger well spacing: typically 500m to 1500m instead of 150m to 400mthe facilities: multi-well injection through common subsea lines, FPSO with no/reduced room for additional facilitiesthe logistics to ship the polymerthe incremental oil evaluation in fields with little to no water injection history

Polymer flooding in very viscous oil has been gaining interest since its efficiency has been field proven. Multiple laboratory investigations have evidenced that the incremental oil recovered by the tertiary process increases considerably the recovery reached thanks to water flooding. However, such tertiary injection is made all the more complex that it is preceded by unstable displacement of oil by water. Therefore a better understanding of the physics is needed, in order to better predict and optimize the viscous oil reserves associated with tertiary polymer flooding. This work presents the interpretation of three similar tertiary polymer flood experiments carried out at the Centre for Integrated Petroleum Research (CIPR, Norway). Each experiment consisted in a water flood followed by a polymer flood. They involved the same Bentheimer outcrop sandstone, 2000 cP oil, 70 cP polymer solution, 2D slab geometry, but different slab lengths (2 slabs are 30cmx30cm, 1 slab is 30cmx90cm). Saturation evolution was monitored by X-ray. On the one hand, provided simple simulation assumptions, the three water floods under study could be history matched (production, pressure). Similar ratios between water and oil relative permeabilities were found, although the water flood relative permeabilities, matched with non Corey-type curves, reflected an important variability. On the other hand, the tertiary polymer floods were found challenging to match consistently. In particular, using classic history matching approaches, the history matching of the long slab experiment could not be reconciled with that of short slab experiments. Simulations were initialized with saturation maps obtained at the end of the water floods. None of the tested approaches enabled us to match consistently the short and long slab experiments together, unless a hysteresis model was implemented. Indeed, a memory effect was observed experimentally from the quantitative analysis of X-ray saturation maps and interpreted as a hysteresis phenomenon. This simple model, with two additional matching parameters, is then further validated by the comparison of 2D simulations with measured in situ saturations.

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A great number of Middle East fields have too harsh reservoir conditions (high temperature, high salinity) for conventional EOR polymers used as mobility control agents. Traditional synthetic polymers such as partially hydrolyzed polyacrylamide (HPAM) are not thermally stable. At temperatures above 70°C, acrylamide moieties hydrolyze to acrylate groups which ultimately may lead to precipitation and total loss of viscosifying power. Thermal stability can be improved by incorporating specific monomers such as ATBS or NVP. However, their polymerization reactivity can cause some compositional drift and limit their molecular weight / viscosifying power. Compared to HPAM, they will require a higher dosage and higher cost. In this study, we present thermal stability and propagation behavior of a new class of synthetic polymers with high thermal stability. In harsh conditions of Middle East brines, with salinity ranging from sea water to 220 g/L TDS, they present excellent thermal stability until temperature as high as 140°C. Adsorption and mobility reduction were evaluated through coreflood experiments using carbonate cores and Clashach sandstone cores, with permeability ranging between 100mD and 700mD. Mobility and permeability reductions indicate a good propagation in both types of rocks. The development of this new polymer is a major breakthrough to overcome the current limits of polymer EOR applications in harsh reservoir conditions. Moreover, molecular weights can be tailored from low to high molecular weights depending on reservoir permeability. Further work is needed to evaluate resistance to mechanical degradation, salt tolerance and adsorption in carbonates and sandstones.