10.1021/acs.energyfuels.6b02230.s001 Lei Zhang Lei Zhang Liming Zheng Liming Zheng Jingyang Pu Jingyang Pu Chunsheng Pu Chunsheng Pu Shuxia Cui Shuxia Cui Influence of Hydrolyzed Polyacrylamide (HPAM) Molecular Weight on the Cross-Linking Reaction of the HPAM/Cr<sup>3+</sup> System and Transportation of the HPAM/Cr<sup>3+</sup> System in Microfractures American Chemical Society 2016 HPAM cross-linking reaction intramolecular cross-linking ends intramolecular cross-linking reaction intramolecular cross-linking stage injection pressure 2016-10-26 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Influence_of_Hydrolyzed_Polyacrylamide_HPAM_Molecular_Weight_on_the_Cross-Linking_Reaction_of_the_HPAM_Cr_sup_3_sup_System_and_Transportation_of_the_HPAM_Cr_sup_3_sup_System_in_Microfractures/4204680 The influence of the molecular weight (<i>M</i><sub>w</sub>) of hydrolyzed polyacrylamide (HPAM) on the cross-linking reaction of HPAM/Cr<sup>3+</sup> and the transportation of HPAM/Cr<sup>3+</sup> in microfractures is systematically studied using viscometry, ultraviolet–visible absorption spectrophotometry, and displacement experiment with a visual microfractured model. The results show that a high-<i>M</i><sub>w</sub> HPAM is advantageous to the intramolecular cross-linking reaction of the HPAM/Cr<sup>3+</sup> system but disadvantageous to the transportation of the HPAM/Cr<sup>3+</sup> system in microfractures. At the intramolecular cross-linking stage, the injection pressure of the HPAM/Cr<sup>3+</sup> system in microfractures is almost equal to that of the HPAM solution, which undergoes no change with the degree of the cross-linking reaction. The higher the HPAM <i>M</i><sub>w</sub>, the earlier the intramolecular cross-linking ends (thus, the intermolecular cross-linking reaction of HPAM/Cr<sup>3+</sup> occurs earlier, which leads to an earlier increase in the injection pressure of the HPAM/Cr<sup>3+</sup> system). Moreover, there is a matching relationship between the fracture aperture and the HPAM/Cr<sup>3+</sup> system to minimize the chromatographic separation when the HPAM/Cr<sup>3+</sup> system transports in the microfracture. For the conformance control of a fractured tight oil reservoir, we conclude that an HPAM/Cr<sup>3+</sup> system with a low-<i>M</i><sub>w</sub> HPAM can more easily enter the deep reservoir to expand the swept volume on a larger scale. However, the system with a high-<i>M</i><sub>w</sub> HPAM can form a gel with a higher viscosity to produce a higher plugging strength.