Spielman-Sun Eleanor, Bland Garret, Wielinski Jonas, Frouté Laura, Kovscek Anthony R, Lowry Gregory V, Bargar John R, Noël Vincent
Environmental Geochemistry Group at SLAC, Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
Department of Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, PA 15289, USA.
Sci Total Environ. 2023 Dec 1;902:166409. doi: 10.1016/j.scitotenv.2023.166409. Epub 2023 Aug 18.
Deep subsurface stimulation processes often promote fluid-rock interactions that can lead to the formation of small colloidal particles that are suspected to migrate through the rock matrix, partially or fully clog pores and microfractures, and promote the mobilization of contaminants. Thus, the goal of this work is to understand the geochemical changes of the host rock in response to reservoir stimulation that promote the formation and migration of colloids. Two different carbonate-rich shales were exposed to different solution pHs (pH = 2 and 7). Iron and other mineral transformations at the shale-fluid interface were first characterized by synchrotron-based XRF mapping. Then, colloids that were able to migrate from the shale into the bulk fluid were characterized by synchrotron-based extended X-ray absorption structure (EXAFS), scanning electron microscopy (SEM), and single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-icpTOF-MS). When exposed to the pH = 2 solution, extensive mineral dissolution and secondary precipitation was observed; iron-(oxyhydr)oxide colloids colocated with silicates were observed by SEM at the fluid-shale interfaces, and the mobilization of chromium and nickel with these iron colloids into the bulk fluid was detected by sp-icpTOF-MS. Iron EXAFS spectra of the solution at the shale-fluid interface suggests the rapid (within minutes) formation of ferrihydrite-like nanoparticles. Thus, we demonstrate that the pH neutralization promotes the mobilization of existing silicate minerals and the rapid formation of new iron colloids. These Fe colloids have the potential to migrate through the shale matrix and mobilize other heavy metals (such as Cr and Ni, in this study) and impacting groundwater quality, as well produced waters from these hydraulic fracturing operations.
深部地下刺激过程通常会促进流体与岩石的相互作用，这可能导致形成小的胶体颗粒，这些颗粒被怀疑会穿过岩石基质迁移，部分或完全堵塞孔隙和微裂缝，并促进污染物的迁移。因此，这项工作的目标是了解宿主岩石在响应促进胶体形成和迁移的储层刺激时的地球化学变化。两种不同的富碳酸盐页岩暴露于不同的溶液pH值（pH = 2和7）。首先通过基于同步加速器的X射线荧光映射来表征页岩 - 流体界面处的铁和其他矿物转变。然后，通过基于同步加速器的扩展X射线吸收结构（EXAFS）、扫描电子显微镜（SEM）和单颗粒电感耦合等离子体飞行时间质谱（sp-icpTOF-MS）来表征能够从页岩迁移到主体流体中的胶体。当暴露于pH = 2的溶液时，观察到广泛的矿物溶解和二次沉淀；通过SEM在流体 - 页岩界面观察到与硅酸盐共定位的铁（氢氧）氧化物胶体，并且通过sp-icpTOF-MS检测到这些铁胶体将铬和镍迁移到主体流体中。页岩 - 流体界面处溶液的铁EXAFS光谱表明（在几分钟内）迅速形成了类水铁矿纳米颗粒。因此，我们证明pH中和促进了现有硅酸盐矿物的迁移以及新铁胶体的快速形成。这些铁胶体有可能穿过页岩基质迁移并迁移其他重金属（如本研究中的铬和镍），并影响地下水质量以及这些水力压裂作业产生的采出水质量。
