A compilation of articles (SPE, EAGE, others) dealing with all aspects of chemical enhanced oil recovery (chemicals, reservoir, design, facilities, etc.). Regular updates – help appreciated!

2023. EAGE IOR+ The Hague.

The workflow used to select and study polymer candidates for polymer flooding has remained relatively unchanged since the first projects were performed in the 1960s. Starting with viscosity curves and filtration test, the polymer candidates are then injected into cores representative of the reservoir from which parameters are extracted for history matching and simulation purposes. Interestingly, all studies follow the same book without questioning the validity of the approaches used or the representativity of the polymer solution studied.

2022.

In this short paper, we will try to address several questions regarding the deployment of polymer flooding and the remaining challenges, while providing a series of guidelines to accelerate the deployment of this technique in maturing oilfields.

2021.

Polymer flooding is a well-established technique aimed at improved recovery factors from oilfields. Among the important parameters affecting the feasibility of a large deployment, polymer retention is one of the most critical since it directly impacts the oil bank delay and therefore the final economics of the project. This paper describes the work performed for the East-Messoyakhskoe oilfield located in Northern Siberia (Russia). A literature review was first performed to select the most appropriate methodology to assess polymer retention in unconsolidated cores at residual oil saturation. 4 polyacrylamide polymers were selected with molecular weights between 7 and 18 M Da and sulfonated monomer (ATBS) content between 0 and 5% molar. An improved 2-fronts dynamic retention method along with total organic carbon—total nitrogen analyzers were used for concentration measurement. Retention values vary between 93 and 444 The sentence could be rephrased  g/g, with the lowest given by the polymers containing ATBS, corroborating other publications on the topic. This paper also summarizes the main learnings gathered during the adaptation of laboratory procedures and paves the way for a faster and more efficient retention estimation for unconsolidated reservoirs.

2016. EAGE IOR.

As of today, the vast majority of chemical enhanced oil recovery projects have been conducted using polymers in powder form. The fact that many of these projects – not to say all – have been implemented onshore is probably part of the explanation. Powders present several advantages which will be described in more detail in the following paragraphs including high active content and longer shelf-life. Nowadays, when considering offshore projects, the use of liquids can at times be more convenient when the weather conditions make the transfer of solids from a boat to a platform more difficult. A smaller equipment footprint is also required when using emulsions compared to solids; this can be a critical parameter when studying the implementation in brown fields with existing facilities. 

2017. SPE185418.

 The selection of the right polymer chemistry in chemical enhanced oil recovery processes is key to successfully increase oil recovery. To start the screening process, it is necessary to look at minimum 3 parameters including brine composition, reservoir temperature and permeability. In addition to simple rheological tests, it is mandatory to evaluate the long-term and shear stabilities of the polymer candidates to ensure that viscosity is maintained over time at an economical concentration. In few cases, the polymer that yields the best results (especially viscosity yield) at an instant t is not always the best compromise when considering long-term stability or shear sensitivity. This paper aims at providing some guidelines to select the optimum chemistry for a wide range of field conditions. 

The resistance of different acrylamide and ATBS-based polymers to salinity and shear is evaluated through viscosity measurements over a wide range of brine compositions. A parameter called R+, that reflects brine hardness, is introduced in this study. Brines considered are either with a constant Total Dissolved Salt (TDS) and varying R+ or different total salinities with a constant R+. This parameter is also used to compare shear resistance of the different polymers. 

For all the polymers, there is a threshold value of R+ beyond which viscosity remains constant. Interestingly, this threshold is reached for lower value of R+ for polymers containing ATBS, a monomer also well-known to provide calcium tolerance. Increasing the amount of ATBS yields better tolerance to divalent cations and provides shear resistance. A minimum amount of sulfonated monomer is required to improve the overall stability in complex brines. 

2016. EAGE IOR. 

Polymer flooding has proven to be an effective technique to improve oil recovery from mature reservoirs. The selection of polymer, focusing mainly on its temperature tolerance properties and its ability to propagate in porous media, is key to achieve a successful EOR job. This selection also depends on brine injection compositions that covers a large range of salinities and hardness worldwide. A screening of viscosity behavior with different polymers in different brine conditions is obviously helpful in order to select the most cost effective chemistry. The impact of different acrylamide based polymer chemistries is evaluated through viscosity measurement over a wide range of salinities and hardness.

A parameter called R+, corresponding to the molar ratio of divalent cations divided by the total mole number of cations in the brine is introduced. Salt tolerance and hardness tolerance of polymers in solutions are evaluated for brine considering either constant Total Dissolved Salt (TDS) with different R+ either the impact of different total salinities for constant R+. This parameter is as well considered to compare shear stability of the different polymers. At least, the impact of the type of divalent cations on viscosity is reported. Polymers from the study are all anionic and acrylamide based. The introduction of different amounts of sulfonated monomer (ATBS) was performed and its impact on hardness and shear tolerance was assessed. For all the polymers, a threshold beyond which viscosity remains constant is reached for R+ > 0,5. Interestingly, this threshold is obtained for lower value of R+ for polymers containing ATBS since they provide better calcium tolerance. Calcium provides a higher impact on viscosity compared to magnesium for all the polymers studied. Increasing the amount of ATBS leads to higher tolerance to divalent cations. It also provides better stability to shear degradation. A minimum amount of sulfonated monomer is required to improve stability. The objective of this paper is to complete guidelines in the selection of industrial polymers considering a wide range of salinities and hardness. The screening of brine and polymers selected for this study is wide enough to represent worldwide injection brine conditions and helps selecting the most appropriate chemistry for each reservoir condition. 

2016. EAGE IOR.

A long but rewarding R&D work has helped successfully deliver a new surfactant formulation which, along with a stable polymer, has been injected into a preselected part of the Algyő field, yielding outstanding results in terms of extra oil recovery. All the aspects have been de-risked including surfactant manufacturing, delivery and quality control, chemical dissolution and injection, safe and reliable operations and, last but not least, quality control procedures taken from the laboratory to the field. This aspect also emphasizes the importance of team work and collaborations between all parties, including the chemical suppliers. 

2016. SPE179834

 This study demonstrates the viability of a cost-effective alternative to what is already used in the Marmul field. This new polymer can be an appropriate candidate to keep chemical EOR in Omani southern fields economically viable. 

2015. SPE177073,

 This paper describes the selection and evaluation of polymers dedicated to high temperature reservoir conditions (from 85°C to 140°C) using very low salinity brine in comparison with harder brine. A series of rheological, shear and thermal stability tests have been performed to select the most appropriate polymer for each case. The impact of the chemical composition and the microstructure shows that the incorporation of NVP is not necessarily required to ensure stability over 6 months above 100°C in soft brines. Results show as well that ATBS improves shear and thermal stability in both soft and hard brine conditions. Besides, the incorporation of thermo-responsive moieties in the polymer improves viscosity properties resulting in a lower dosage even at high temperature to reach target viscosity. 

2013. SPE165249. Bonnier et al.

This paper presents recent developments of in-line viscometer which can measure the viscosity at low shear as per real reservoir conditions.

2015. SPE174618.

This paper describes a new class of polymers, called “stimuli-responsive”, which has been designed to overcome the aforementioned challenges. This new family of polyacrylamide-based polymers has structurally modified to counterbalance the negative effect of salinity and temperature encountered during the transit through the reservoir. The placement, number and quantity of stimuliresponsive grafts can be finetuned to each reservoir condition to develop its full potential in the subterranean formation. This variable comes on top of other possible adjustments made to the polymer backbone including molecular weight, hydrolysis and incorporation of thermostable groups such as ATBS (acrylamide tertio butyl sulfonic acid) and/or NVP (Nvinyl pyrrolidone).

A series of rheological tests has been performed to demonstrate several features of the solutions prepared from these polymers, including salinity resistance, effect of temperature and longterm stability tests. Moreover, injectivity and retention tests have been performed to evaluate the behavior of these polymers in porous medium. A reduction in the polymer dosage on the injection side and the stimuli responsive behavior of the polymer also open new opportunities to minimize the impact of the presence of said polymer in the coproduced water on surface facilities. Some preliminary experiments have been performed in these directions.

The objective of the study is also to demonstrate the possibility to develop innovative and cost-effective polymers for each reservoir condition. It encompasses an early and particularly close cooperation between the polymer manufacturer and the company willing to improve oil recovery from its reservoirs.

2013. SPE164072

The properties of novel polymers for proppant transport in hydraulic fracturing operations are discussed. Acrylamide based associative polymers have been synthesized using various industrial production processes. Anionic polymers investigated are acrylamide (AMD) based co- and ter-polymers functionalized with monomers such as sodium acrylate (AA), sodium acrylamido-tertiary-butyl sulfonate (ATBS) and a home-made surfactant monomer. The rheological properties of the developed polymers in different brines are evaluated and compared to commercial guar gums usually used for fracturing fluids. The viscoelastic properties as well as settling time of proppant in graduated cylinder have been evaluated. The impact of oxidizing breakers and surfactants added to increase or decrease the viscosity of solutions are reported as well. The new polymers can be used in slickwater, linear gel and cross-linked hydraulic fracturing fluid. They have the ability to carry the proppant down to the target zone. With this technology, proppant can be transported and placed into the fractures with lower concentrations of product and reduce or eliminate the need for using guar gum. Fluid viscosity can be controlled (either increased or decreased) by the addition of surfactants and broken by conventional oxidizers.

2013. EAGE IOR>

The propagation of associative HPAM polymers in porous media is greatly dependent on the degree of hydrophobic modification. In this paper, the transport properties of several associative polymers with degree of association from none to high were investigated in Berea cores and silica sand-pack cores. The associative polymer solutions with customary bulk viscosities generated resistance factors that varied significantly, ranging from 10 to over 500. The increasing resistance factors were attributed to the higher level of polymer retention as the degree of association increased. On the other hand, two associative polymers, with a similar degree of association but different molecular weight and bulk viscosities generated similar resistance factors. Hence the effect of molecular weight and bulk viscosity is not as significant as hydrophobic modification in generating in-situ flow resistance. Linear coreflood tests were conducted to evaluate the potential of associative polymer flooding in recovering western Canadian heavy oil with viscosity of 18,700 mPa.s in 3-Darcy sandpacks. The properly selected associative polymer was able to propagate through the sandpack with no significant retention and generate in-situ apparent viscosity twice as high as the unmodified HPAM.

2013. A. Thomas, N. Gaillard, C. Favéro.

Among Chemical Enhanced Oil Recovery (CEOR) methods, polymer flooding is a straightforward technique with a long commercial history and proven results. It consists in injecting polymer-augmented water into a subterranean formation in order to improve, thanks to the viscosity increase, the sweep efficiency in the reservoir and provides a mobility control between water and the hydrocarbons.

However, implementing successfully a polymer flood in the field requires specific know-how to avoid polymer degradation and associated viscosity loss.

Oil & Gas Science and Technology – Rev. IFP Energies nouvelles, Vol. 67 (2012), No. 6, pp. 887-902 Copyright © 2013, IFP Energies nouvelles DOI: 10.2516/ogst2012065

A. Thomas, “Polymer Flooding”, in Chemical Enhanced Oil Recovery (cEOR) – a Practical Overview. London, United Kingdom: IntechOpen, 2016 [Online].

The focus of this chapter is on polymers and their use to enhance oil recovery through the process known as polymer flooding. Emphasis is given to practical information relevant to field application(s) of polymer flooding. Therefore, the purpose of this chapter is to provide a brief but thorough overview of key concepts necessary to understand this technology for its successful implementation in the field.