Hydrodynamics of Overpressuring in the Sacramento Valley, California

9526951加文区域超压是萨克拉门托山谷和加利福尼亚州海岸山脉的特征。任何沉积层序中高流体压力的产生和维持都需要两个基本条件：(1)低渗透封闭单元和(2)增加这些岩石内孔隙压力的地质力。这些力可能是构造的、热的，甚至是化学的。这项研究的目的是确定哪些因素在加州中央山谷超压区的形成中起作用，并量化每个因素的贡献，以便成功地模拟该地区目前发现的高压。加州大谷或中央谷的沉积盆地拥有区域含水层，在更深的地方拥有大型石油储集层。地质和地球化学数据丰富，因为该山谷已被广泛勘探并绘制了这些自然资源的地图。北部的萨克拉门托盆地蕴藏着丰富的天然气和地热资源，盆地西部靠近海岸山脉的深层地下水(深度超过700米)明显超压。尽管地质勘探有很长的历史，但很少有水文地质学工作来量化大峡谷超压等地质过程的深层地下水流动的性质。这项提议旨在增加我们对萨克拉门托盆地深层地下水流动系统如何随着地质时间的推移而演变的基本理解。早期对萨克拉门托盆地的研究表明，异常高的流体压力的起源与构造挤压有关。根据Berry(1973)的概念模型，与圣安德烈亚斯断层和盆地和山脉省有关的东西向挤压像构造虎钳一样“挤压”了大山谷的沉积物，推动深孔隙水向上。由于厚厚的海相泥岩段渗透率低，这些作用力产生了高压区。然而，其他超压机制可能是重要的。石油生成、脱水反应、地壳加热和快速下沉是其他需要考虑和量化的水动力学机制。因此，这项建议的主要目标是将水文地质模拟作为一种工具，用来量化山谷深水和浅水水流系统之间的关系，并测试超压概念模型的可行性。各种类型的野外观测将被用来对水文地质模型施加约束，但我们主要将汇编来自深探井的压力数据。这里提出的这项工作代表了量化加州大谷“深层”地下水流动动力学的第一次努力。对地质概念的水文测试和耦合的数学模型构成了研究的核心：萨克拉门托盆地的流体力学模型应该揭示地壳超压起源的其他原因。此外，硅谷拥有世界上最大的淡水含水层系统之一，水资源十分宝贵。增进我们对盆地地下水系统的了解，对于了解浅层淡水含水层的潜在盐分污染可能有很大的实际益处，因为发展继续满足对饮用水日益增长的需求。

9526951 Garven Regional overpressuring is a phenomenon characteristic of the Sacramento Valley and the Coast Ranges of California. The creation and maintenance of high fluid pressures in any sedimentary sequence require two basic conditions: (1) low-permeability confining units and (2) geologic forces which increase the pore pressure within these rocks. The forces may be tectonic, thermal, or even chemical in nature. The intent of this study is to determine which factors play a role in the creation of overpressure zones in the Central Valley of California and to quantify the contribution of each in order to successfully model the high pressures currently found in the region. Sedimentary basins in the Great or Central Valley of California host regional aquifers and at greater depths host large petroleum reservoirs. Geological and geochemical data are abundant, as the Valley has been extensively explored and mapped for these natural resources. The Sacramento Basin in the north is rich in natural gas and geothermal resources, and deep groundwater (depths greater than 700 m) is noticeably overpressured in the western part of the basin near the Coast Ranges. Despite the long history of geologic exploration, very little hydrogeologic work has been done to quantify the nature of deep groundwater flow of geologic processes such as overpressuring in the Great Valley. This proposal seeks to increase our basic understanding of how the deep groundwater flow systems have evolved over geologic time in the Sacramento Basin. Earlier studies on the Sacramento Basin suggest that the origin of anomalously high fluid pressures is related to tectonic compression. According to the conceptual model of Berry (1973), east-west compression associated with the San Andreas Fault and the Basin and Range province "squeezed" the Great Valley sediments like a tectonic vise, driving deep pore waters upward. These forces generated high pressure zones due to the low permeability of the thick marine mudstone sectio n. However, other mechanisms for overpressuring may be important. Petroleum generation, dehydration reactions, crustal heating, and rapid subsidence are other mechanisms that need to be considered and quantified hydrodynamically. A primary objective of this proposal therefore is to use hydrogeologic modeling as a tool for quantifying the relationship between the deep ad shallow flow systems in the Valley and test the viability of conceptual models for overprssuring . Various types of field observations will be used to place constraints on the hydrogeologic models, but mostly we will compile pressure data from deep exploration wells. The work proposed here represents the first effort to quantify "deep" groundwater flow dynamics in the Great Valley of California. Hydrologic testing of geologic concepts with coupled mathematical models form the heart of the study: hydromechanical model of the Sacramento Basin ought to shed basic light on other causes for for the origin of overpressures I the Earth's crust. Furthermore, water resources are precious in the Valley which contains one of the largest fresh-water aquifer systems in the world. Improving our understanding of the basin groundwater systems may have significant practical benefit with regard to understanding of the potential salinity contamination of the shallow, fresh-water aquifers as development continues to satisfy an over increasing demand for potable water.