DOE EFRC─Center for Mechanistic Control of Water-Hydrocarbon-Rock Interactions in Unconventional and Tight Oil Formations, Stanford University, Stanford, California 94305, United States.
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States.
Chem Rev. 2022 May 11;122(9):9198-9263. doi: 10.1021/acs.chemrev.1c00504. Epub 2022 Apr 11.
Hydraulic fracturing of unconventional oil/gas shales has changed the energy landscape of the U.S. Recovery of hydrocarbons from tight, hydraulically fractured shales is a highly inefficient process, with estimated recoveries of <25% for natural gas and <5% for oil. This review focuses on the complex chemical interactions of additives in hydraulic fracturing fluid (HFF) with minerals and organic matter in oil/gas shales. These interactions are intended to increase hydrocarbon recovery by increasing porosities and permeabilities of tight shales. However, fluid-shale interactions result in the dissolution of shale minerals and the release and transport of chemical components. They also result in mineral precipitation in the shale matrix, which can reduce permeability, porosity, and hydrocarbon recovery. Competition between mineral dissolution and mineral precipitation processes influences the amounts of oil and gas recovered. We review the temporal/spatial origins and distribution of unconventional oil/gas shales from mudstones and shales, followed by discussion of their global and U.S. distributions and compositional differences from different U.S. sedimentary basins. We discuss the major types of chemical additives in HFF with their intended purposes, including drilling muds. Fracture distribution, porosity, permeability, and the identity and molecular-level speciation of minerals and organic matter in oil/gas shales throughout the hydraulic fracturing process are discussed. Also discussed are analysis methods used in characterizing oil/gas shales before and after hydraulic fracturing, including permeametry and porosimetry measurements, X-ray diffraction/Rietveld refinement, X-ray computed tomography, scanning/transmission electron microscopy, and laboratory- and synchrotron-based imaging/spectroscopic methods. Reactive transport and spatial scaling are discussed in some detail in order to relate fundamental molecular-scale processes to fluid transport. Our review concludes with a discussion of potential environmental impacts of hydraulic fracturing and important knowledge gaps that must be bridged to achieve improved mechanistic understanding of fluid transport in oil/gas shales.
非常规石油/天然气页岩的水力压裂改变了美国的能源格局。从致密的水力压裂页岩中回收碳氢化合物是一个效率非常低的过程，天然气的估计回收率<25%，石油的<5%。本综述重点讨论了水力压裂液（HFF）中的添加剂与石油/天然气页岩中的矿物和有机物之间复杂的化学相互作用。这些相互作用旨在通过增加致密页岩的孔隙度和渗透率来提高碳氢化合物的回收率。然而，流体-页岩的相互作用导致页岩矿物的溶解以及化学组分的释放和传输。它们还导致页岩基质中的矿物沉淀，从而降低渗透率、孔隙度和碳氢化合物的回收率。矿物溶解和矿物沉淀过程之间的竞争影响了回收的石油和天然气的数量。我们回顾了泥岩和页岩中非常规石油/天然气页岩的时空起源和分布，然后讨论了它们在全球和美国的分布以及来自不同美国沉积盆地的组成差异。我们讨论了 HFF 中的主要类型的化学添加剂及其预期用途，包括钻井泥浆。讨论了水力压裂过程中整个油/气页岩的裂缝分布、孔隙度、渗透率以及矿物和有机物的身份和分子水平形态。还讨论了用于在水力压裂前后表征油/气页岩的分析方法，包括渗透率和孔隙率测量、X 射线衍射/Rietveld 精修、X 射线计算机断层扫描、扫描/透射电子显微镜以及基于实验室和同步辐射的成像/光谱方法。为了将基本的分子尺度过程与流体传输联系起来，我们详细讨论了反应传输和空间尺度。我们的综述以讨论水力压裂的潜在环境影响以及必须弥合的重要知识差距结束，以实现对油/气页岩中流体传输的更好的机制理解。
