Gizatullin Bulat, Mattea Carlos, Shikhov Igor, Arns Christoph, Stapf Siegfried
FG Technische Physik II/Polymerphysik, Technische Universität Ilmenau, D-98684 Ilmenau, Germany.
School of Minerals and Energy Resources Engineering, Univ. of New South Wales, Sydney, NSW 2052, Australia.
Langmuir. 2022 Sep 13;38(36):11033-11053. doi: 10.1021/acs.langmuir.2c01681. Epub 2022 Sep 1.
Three types of natural rocks─Bentheimer and Berea sandstones, as well as Liège Chalk─have been aged by immersion in a bitumen solution for extended periods of time in two steps, changing the surface conditions from water-wet to oil-wet. NMR relaxation dispersion measurements were carried out on water and oil constituents, with saturated and aromatic molecules considered individually. In order to separate the different relaxation mechanisms discussed in the literature, H and F relaxation times were compared to H for fully deuterated liquids: while H relaxes predominantly by quadrupolar coupling, which is an intramolecular process, the remaining nuclei relax by dipolar coupling, which potentially consists of intra- and intermolecular contributions. The wettability change becomes evident in an increase of relaxation rates for oil and a corresponding decrease for water. However, this expected behavior dominates only for the spin-lattice relaxation rate at very low field strengths and for the spin-spin relaxation rate , while high-field longitudinal relaxation shows a much weaker or even reverse trend. This is attributed in part to a change of radical concentration on the pore surface upon coverage of the native rock surface by bitumen as well as by the change of surface chemistry and roughness. EPR and DNP measurements quantify the change of volume vs surface radical concentration in the rocks, and an improved understanding of the role of relaxation via paramagnetic centers is obtained. By means of comparing different fluids and nuclei in combination with a defined wettability change of natural rocks, a refined model for molecular dynamics in conjunction with NMR relaxation dispersion is proposed.
三种天然岩石——本特海默砂岩、贝雷亚砂岩以及列日白垩——通过在沥青溶液中长时间浸泡分两步进行老化处理，使表面条件从水湿变为油湿。对水和油成分进行了核磁共振弛豫色散测量，分别考虑了饱和分子和芳香分子。为了区分文献中讨论的不同弛豫机制，将氘代完全的液体中的氢和氟弛豫时间与氢进行了比较：氢主要通过四极耦合弛豫，这是一个分子内过程，而其余原子核通过偶极耦合弛豫，偶极耦合可能由分子内和分子间贡献组成。润湿性变化表现为油的弛豫率增加以及水的弛豫率相应降低。然而，这种预期行为仅在非常低场强下的自旋晶格弛豫率以及自旋 - 自旋弛豫率中占主导，而高场纵向弛豫显示出弱得多甚至相反的趋势。这部分归因于沥青覆盖天然岩石表面后孔隙表面自由基浓度的变化以及表面化学和粗糙度的变化。电子顺磁共振（EPR）和动态核极化（DNP）测量量化了岩石中体积与表面自由基浓度的变化，并且对通过顺磁中心的弛豫作用有了更好的理解。通过比较不同流体和原子核，并结合天然岩石确定的润湿性变化，提出了一个结合核磁共振弛豫色散的分子动力学精细模型。
