Hydrodynamic and Geochemical Interactions Between Formation Waters of Varying Salinity

地下孔隙流体的盐度范围从大气降水(0g/L)到高盐卤水(300g/L)，而温度和压力影响这些孔隙水的密度和粘度。孔隙流体密度的空间变化可能驱动或抑制孔隙流体运动。不同矿化度的孔隙流体在靠近时可能会发生物理和/或化学上的相互作用。这可能是因为：1)大气降水通过地形补给驱动的盆地(例如，阿拉斯加北坡)；2)盐的溶解和随后的浮力驱动流绕着盐构造(例如，墨西哥湾近海的Marchand Dome或Bullwinkle油田)；以及3)沿断层或裂缝网络(例如，威尔科克斯地层，路易斯安那州陆上或尤金岛，墨西哥湾近海)的地压流体的幕式排出。以往的研究做了一些简化的假设，例如忽略压力和浮力驱动的流动，或者忽略矿化度对孔隙流体密度或粘度的影响。我们提出的基本问题是，当压力和密度都不同时，不同矿化度的孔隙流体如何相互作用，以及同时发生的流体-岩石化学作用如何影响多孔介质的输运性质。为此，我们获得了路易斯安那州南部和北坡前陆盆地沉积物和地层水的结构、地层和物理/化学性质的数据集。该项目是一项为期三年的关于阿拉斯加和墨西哥湾北坡流体流动、质量传输和反应方面的研究：(1)利用电缆测井、地震数据、地层水和沉积物样品确定地层水和沉积物性质、溶质运移路径和水-沉积物化学反应的空间变化；(2)研究密度驱动和压力驱动的流体流动及相关的热和溶质迁移。数据将被用来检验我们的假设，以及评估在以前的变密度流体流动的数学和数值解中所做的简化假设的有效性。我们将研究两个具体的例子：1)当它通过盆地与深部的卤水或溶解的盐构造上方的卤水相互作用时的大气补给；以及2)从溶解的盐构造向下移动的卤水羽流，与从地压带排出的较新鲜的地层水相互作用。在这两种情况下，我们都想知道淡水是否会在物理上与盐水混合、取代盐水或压过盐水，以及是什么因素控制了这种反应。了解不同矿化度的流体如何在地下相互作用，对于沿海含水层、地下水资源、石油勘探、含水层修复、二氧化碳封存和危险废物处理具有重要意义。如果卤水真的不能移动，深埋在地下的高盐度盐水可能是危险物质的储存库。或者，孔隙水矿化度的空间变化可能会导致密度驱动的流体流动，或者指示拟议的二氧化碳封存地点、油田或咸水入侵修复项目中的迁移路径或溢出点。该项目通过开发几个数据集和增强现有的变密度流体流动模拟程序，为科学界提供一般服务。

Pore fluids in the subsurface range in salinity from meteoric (0 g/l) to hypersaline brines ( 300 g/l), while temperature and pressure affect the density and viscosity of these pore waters. Spatial variations in pore fluid density may drive or inhibit pore fluid motion. Pore fluids of different salinities may physically and/or chemically interact when they are brought into close proximity. This may occur as: 1) meteoric water moves through a basin driven by topographic recharge (e.g., North Slope of Alaska); 2) dissolution of salt and subsequent buoyancy drive flow around salt structures (e.g., Marchand Dome or Bullwinkle field, offshore Gulf of Mexico); and 3) episodic expulsion of geopressured fluids along faults or fracture networks (e.g., Wilcox formation, onshore Louisiana or Eugene Island, offshore Gulf of Mexico). Previous studies have made simplifying assumptions, such as ignoring pressure and buoyancy driven flow or the effect of salinity on pore fluid density or viscosity. We propose to address fundamental questions as to how pore fluids of variable salinity interact when both pressure and density, as well as how concurrent fluid-rock chemical interactions affect the transport properties of the porous medium. Toward this end, we have acquired data sets on the structure, stratigraphy and physical/chemical properties of sediments and formation waters in south Louisiana and the North Slope foreland basin. This project is a three-year study on the following aspects of fluid flow, mass transport and reaction in the North Slope of Alaska and Gulf of Mexico: (1) a determination of spatial variations in formation water and sediment properties, solute transport pathways and water-sediment chemical reactions using wireline logs, seismic data, formation water and sediment samples; and (2) a study of coupled density-driven and pressure-driven fluid flow and associated heat and solute transport. Data will be used to test our hypotheses as well as assess the validity of simplifying assumptions made in previous mathematical and numerical solutions of variable-density fluid flow. We will study two specific examples: 1) meteoric recharge as it moves through a basin interacting with brine at depth or brine above a dissolving salt structure; and 2) a brine plume moving down dip from a dissolving salt structure interacting with fresher formation waters being expulsed from a geopressured zone. In both cases we wish to know whether fresh water will physically mix with the brine, displace the brine, or ride over the brine, and what factors control that response. Understanding how fluids of variable salinity interact in the subsurface has important implications for coastal aquifers, groundwater resources, oil exploration, aquifer remediation, CO2 sequestration, and hazardous waste disposal. Deeply buried hypersaline brine might be a repository for hazardous material if brines are truly immobile. Alternatively, spatial variations in pore water salinity might induce density driven fluid flow or indicate migration pathways or spill points in a proposed CO2 sequestration site, an oil field, or a salt water intrusion remediation project. This project provides general service to the science community by development of several data sets and enhancement of existing variable density fluid flow simulation codes.