Characterization of Ultrahigh-Molecular-Weight Oilfield Polyacrylamides Under Different pH Environments by Use of Asymmetrical-Flow Field-Flow Fractionation and Multiangle-Light-Scattering Detector
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Résumé
Summary Various types of ultrahigh-molar-mass polyacrylamides (HPAMs) and their copolymers and terpolymers used not only in enhanced oil recovery (EOR) but also in drilling, fracturing, water treatment, and tailing applications require an accurate description of polymer molar mass (Mw) and hydrodynamic size for their optimal design. The range of Mw for various types of available HPAMs is between 4 and 30 million g/mol and is typically determined by use of intrinsic-viscosity measurement. Molecular-weight distribution (MWD) cannot be determined because neither standard with low polydispersity index (PDI) nor gel-permeation-chromatography (GPC) or size-exclusion-chromatography (SEC) techniques exist today for such ultrahigh-molar-mass polymers. Moreover, the solution environment in underground reservoirs, characterized by high temperatures, pH values, and the presence of monovalent and divalent ions, may often lead to changes in polymer-macromolecular conformation. Current techniques, SEC, ultraviolet-visible measurements, and liquid chromatography, are not capable of accurately investigating these complex macromolecular structures for various reasons. In this paper, the asymmetrical-flow field-flow fractionation (AF4) system was used to fractionate four different ultrahigh-molecular-weight HPAM samples, varying in molar mass and commercially used for oilfield applications, in various carrier pH values ranging from 12 to 3 (pH values of 12, 7.4, and 3). The system uses field-flow fractionation (FFF), a family of analytical techniques developed specifically for separating and characterizing macromolecules, colloids, and particles. The theoretical separation range for AF4 is between 103 to 1012 g/mol. Other advantages over conventional GPC/SEC include minimum shear degradation, mild operating conditions, and no sample loss caused by adsorption. The flow system was equipped with a multiangle-light-scattering (MALS) and refractive-index (RI) detectors to measure molar mass and radius of gyration (Rg). The results show that the observed molecular weight of the polymer aggregate increased substantially as the pH value of the carrier solution decreased from 12 to 3, especially for higher-molar-mass polymers. The sample Rg showed the opposite trend, decreasing as the pH of the carrier solution changed from basic to acidic. For ultrahigh molecular HPAM at high pH, a narrower molar mass and radius distribution was observed with disaggregated molar mass and increased branching or swelling (therefore larger hydrodynamic radius). Use of this direct separation and measurement technique can improve understanding of polymer-macromolecular structure and corresponding changes in the reservoir brines.
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Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,001 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
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