Collaborative Research: Paleohydrology of the Illinois Basin--Effects of Glaciation on Fluid Flow, Solute Transport, and Microbial Methane Generation

劳伦蒂冰盖的融化在过去的200万年里深刻地改变了北美的地下水和地表水文。冰下融水沿着低洼的古生代盆地边缘渗入盐渍含水层，逆转了地下水流动方向，并将淡水-咸水混合带压制到1公里深以上。裂隙富有机页岩中微生物甲烷的经济聚集区位于盆地边缘的淡水补给区。我们将评估更新世冰川负荷和永久冻土发展对伊利诺伊盆地大气水补给历史和循环的影响，重点是两个含有微生物甲烷的有机富集区(晚泥盆世新奥尔巴尼页岩、宾夕法尼亚煤)和邻近的区域含水层系统。这项研究的结果将极大地扩展我们对冰盖-含水层相互作用、承压地下水的年龄分布以及深部地下微生物活动的水文地球化学控制的理解。形成水、天然气和微生物样本将从新奥尔巴尼页岩、宾夕法尼亚煤层甲烷带和邻近区域含水层沿伊利诺伊盆地中部到盆地东北边缘的横断面上的约50口生产油气和家庭井中采集。我们将分析地层水和天然气的元素和稳定同位素(O、H、C)化学、14C和惰性气体。此外，还将通过DNA分析确定微生物种群，并对存档的页岩和煤炭材料进行碳氢化合物生物降解性分析。我们最近开发了一个新的水文模型，用于求解流体运动、热、多组分(盐度、稳定/放射性同位素和惰性气体)溶质运移、永久冻土和岩石圈挠曲/地幔流动等方程。该模型将与观测到的盐度和同位素示踪剂进行比较，以检验冰盖动力学在晚更新世期间显著改变了伊利诺伊盆地管道的假设。尽管对伊利诺伊盆地的古水文学进行了大量研究，但在深盆地含水层中维持来自海相的高盐度流体仍然是一个谜。这项研究将有助于限制卤水和淡水资源在沉积盆地中的停留时间，以及驱动大陆尺度的流体和溶质运移所需的水动力，以对抗强烈的盐度梯度。这项研究的结果还将有助于限制在非常规储集层(如破碎的黑色页岩和煤层)进行经济天然气聚集所需的水文和地球化学条件。重要的是，这个多学科的项目将是亚利桑那大学博士生论文的组成部分，并涉及几名本科生研究人员。

Melting of the Laurentide Ice Sheet profoundly altered the groundwater and surface hydrology of North America over the last 2 million years. Subglacial meltwaters infiltrated into saline aquifers along the margins of low-lying Paleozoic basins, reversing groundwater flow directions and suppressing the freshwater-saline water mixing zones to over 1 kilometer depth. Economic accumulations of microbial methane in fractured organic-rich shales are located in areas of freshwater recharge along the basin margins. We will assess the impact of Pleistocene glacial loading and permafrost development on recharge history and circulation of meteoric waters in the Illinois Basin, focusing on two organic-rich zones that contain microbial methane (Late Devonian New Albany Shale, Pennsylvanian coals), and adjacent regional aquifer systems. Results of this study will greatly expand our understanding of ice sheet-aquifer interactions, age distribution of confined groundwaters, and hydrogeochemical controls on microbial activity in the deep subsurface.Formation waters, gas, and microbial samples will be collected from ~50 producing oil/gas and household wells in the New Albany Shale, Pennsylvanian Coalbed Methane Play, and adjacent regional aquifers, along a transect from the central Illinois Basin to the northeastern basin margin. We will analyze the elemental and stable isotope (O,H,C) chemistry, 14C, and noble gases of formation waters and gas. In addition, microbial populations will be determined by DNA analyses, and archived shale and coal materials will be analyzed for biodegradation of hydrocarbons. We have recently developed a new hydrologic model, which solves equations for fluid motion, heat, multi-species (salinity, stable/radiometric isotope, and noble gas) solute transport, permafrost, and lithosphere flexure/mantle flow. This model will be compared to observed salinity and isotope tracers to test the hypothesis that ice sheet dynamics has substantially modified the plumbing of the Illinois Basin during the Late Pleistocene.Despite numerous studies of the paleohydrology of the Illinois Basin the maintenance of high salinity fluids of marine-origin in deep basin aquifers is still enigmatic. This study will help to constrain the residence times of brines and freshwater resources in sedimentary basins, and hydrodynamic forces required to drive continental-scale fluid and solute transport against strong salinity gradients. Results from this study will also help to constrain the hydrologic and geochemical conditions necessary for economic gas accumulation in unconventional reservoirs, such as fractured black shales and coalbeds. Importantly, this multi-disciplinary project will be an integral part of a University of Arizona Ph.D. student's thesis, and involve several undergraduate researchers.