Grant Ferguson

Hydrogeological processes in seasonally frozen northern latitudes: understanding, gaps and challenges

The groundwater regime in seasonally frozen regions of the world exhibits distinct behavior. This paper presents an overview of flow and associated heat and solute transport processes in the subsurface, from the soil/vadose zone, through groundwater recharge to groundwater discharge processes in these areas. Theoretical developments, field studies and model development are considered. An illustrative conceptual model of the system is presented. From a groundwater perspective, the dominant effect is the extent of hydraulic isolation between the water above and that below the near-surface frozen zone. The spatial and temporal occurrences of this isolation are seasonally variable and may also be modified under a future changing climate. A good qualitative conceptual understanding of the system has been developed over numerous decades of study. A major gap is the inability to effectively monitor processes in the field, particularly unfrozen water content during freezing conditions. Modeling of field-scale behavior represents a major challenge, even while physically based models continue to improve. It is suggested that progress can be made by combining well-designed field experiments with modeling studies. A major motivation for improving quantification of these processes derives from the need to better predict the impacts of a future changing climate.RésuméLe régime de l’eau souterraine dans les régions gelées de façon saisonnière fait apparaître différents comportements. Cet article présente une vue d’ensemble du flux et des processus de transport de chaleur et de solutés en sub-surface, depuis la zone sol/vadose, à travers des processus de recharge-décharge dans ces zones. Des développements théoriques, études de terrain et développement de modèles sont considérés. Un modèle conceptuel est présenté pour illustrer. Si l’on considère l’eau de nappe, l’effet dominant est l’importance de l’isolation hydraulique entre l’eau sur et l’eau sous la sub-surface gelée. Dans le temps et dans l’espace cette isolation varie avec les saisons et pourra aussi être modifiée par un futur changement du climat. Une bonne compréhension conceptuelle qualitative du système a été développée durant de nombreuses décades d’étude. Une lacune majeure est l’impossibilité de contrôler effectivement le processus sur le terrain, particulièrement la teneur en eau libre durant les périodes de gel. La modélisation du comportement à l’échelle du terrain représente un défi majeur, même si les modèles à base physique continuent de s’améliorer. On suggère que des progrès peuvent être faits en combinant des expériences de terrain bien conçues et des études de modélisation. Une motivation majeure pour améliorer la quantification de ces processus dérive du besoin de mieux prévoir les impacts d’un futur changement climatique.ResumenEl régimen de agua subterránea en regiones estacionalmente congeladas del mundo exhibe comportamientos distintivos. Este trabajo presenta un panorama del flujo y los procesos asociados de transporte de calor y soluto en el subsuelo, a partir de la zona vadosa / suelo, a través de los procesos de recarga a la descarga del agua subterránea en estas áreas. Se consideran los desarrollos teóricos, los estudios de campo y los modelos desarrollados. Se presenta un modelo conceptual ilustrativo del sistema. Desde la perspectiva del agua subterránea, el efecto dominante es el grado de aislamiento entre el agua por encima y por debajo de la zona congelada próxima a la superficie. La presencia espacial y temporal de este aislamiento es variable estacionalmente y pueden también ser modificadas bajo un futuro cambio climático. Un buen entendimiento cualitativo conceptual del sistema se desarrolló durante numerosas décadas de estudio. Una dificultad mayor es la incapacidad para monitorear efectivamente los procesos en el campo, particularmente el contenido de agua no congelada durante las condiciones de congelamiento. El comportamiento modelado a escala de campo representa un desafío mayor, aun cuando los modelos de bases físicas pueden seguir mejorando. Se sugiere que se puede avanzar mediante la combinación de experimentos de campo bien diseñados con estudios de modelos. Una motivación mayor para mejorar la cuantificación de estos procesos deriva de la necesidad de predecir mejor los impactos de un futuro cambio climático.摘要世界上季节性冻土区的地下水动态呈现出不同的行为特征。本文对这些地区的地面以下,从土壤/渗流区通过地下水的补给到地下水的排泄过程的水流运动和相关的热、溶质运移过程作了一个概述。本文综合考虑了理论的发展,场地的研究和模型的发展。另外,文中还展示了一个解释说明性的系统概念模型。从地下水的角度来说,占优势的效应是近地表的冻土区上、下的地下水间的水力隔绝程度。时间、空间上这种隔绝的存在是随着季节变化的,可以在未来变化的气候下进行模拟。通过几十年的研究,对季节性冻土系统的较好的定性概念性认识已经建立起来了。一个主要的不足在于无法有效地监测场地的过程,特别是在严寒条件下不冻水的成分。甚至当基于物理的模型在继续向前发展时,场地尺度上的行为模拟仍是一个主要的挑战。文中指出,可以通过将设计精良的场地试验与模型研究相结合来获得突破。提高这些过程的定量化的主要动机来源于更好地对未来气候变化影响的预测的需求。ResumoO regime de águas subterrâneas em regiões do mundo sazonalmente geladas exibe comportamento distinto. Este artigo apresenta uma visão geral dos processos subsuperficiais de fluxo e de transporte de calor e de soluto associados, desde o solo/zona vadosa, através dos processos de recarga de águas subterrâneas, até à sua descarga. São considerados desenvolvimentos teóricos, estudos de campo e desenvolvimento de modelos. É apresentado um modelo concetual ilustrativo do sistema. Da perspetiva das águas subterrâneas, o efeito dominante é a extensão do isolamento hidráulico entre as águas acima e abaixo da zona gelada próxima da superfície. As ocorrências espaciais e temporais destes isolamentos são variáveis sazonalmente e podem também ser modificadas num clima futuro em mudança. Ao longo de numerosas décadas de estudo, desenvolveu-se uma boa compreensão concetual qualitativa do sistema. Uma grande lacuna é a incapacidade de monitorizar eficazmente os processos no terreno, particularmente o teor de água não solidificada durante condições de congelação. A modelação do comportamento à escala do terreno representa um desafio maior, mesmo enquanto os modelos físicos continuam a melhorar. Sugere-se que se pode conseguir uma boa progressão combinando experiências de terreno bem concebidas com estudos de modelação. Uma motivação principal para melhorar a quantificação destes processos deriva da necessidade de prever melhor os impactes de alterações climáticas futuras.

The isotopic composition of the Laurentide Ice Sheet and fossil groundwater

Stable isotopes have been used to study large-scale changes in hydrology during the Pleistocene epoch. Many of these efforts have required an estimate of the δ18O value of runoff generated by melting ice sheets. There is no consensus on representative values. Here we examine δ18O values from fossil groundwater samples and isotope-enabled general circulation models (GCMs) to better understand the isotopic composition of the Laurentide Ice Sheet (LIS). Groundwater δ18O values ranged from −12.5 to −25.3‰ and tended to increase southward. The δ18O precipitation values predicted by GCMs follow a similar trend but increase more steeply southward. The difference in groundwater and GCM output can be explained by invoking movement of glacial ice and meltwater, along with mixing within groundwater systems. Most groundwater δ18O values are higher than an average LIS δ18O value of −25.4 ± 2.5‰ calculated based on estimated ice sheet volumes and sea level data.

Deep Injection of Waste Water in the Western Canada Sedimentary Basin

Injection of wastes into the deep subsurface has become a contentious issue, particularly in emerging regions of oil and gas production. Experience in other regions suggests that injection is an effective waste management practice and that widespread environmental damage is unlikely. Over the past several decades, 23 km(3) of water has been injected into the Western Canada Sedimentary Basin (WCSB). The oil and gas industry has injected most of this water but large amounts of injection are associated with mining activities. The amount of water injected into this basin during the past century is 2 to 3 orders magnitude greater than natural recharge to deep formations in the WCSB. Despite this large-scale disturbance to the hydrogeological system, there have been few documented cases of environmental problems related to injection wells. Deep injection of waste appears to be a low risk activity based on this experience but monitoring efforts are insufficient to make definitive statements. Serious uncharacterized legacy issues could be present. Initiating more comprehensive monitoring and research programs on the effects of injection in the WCSB could provide insight into the risks associated with injection in less developed sedimentary basins.

Screening for heat transport by groundwater in closed geothermal systems.

Heat transfer due to groundwater flow can significantly affect closed geothermal systems. Here, a screening method is developed, based on Peclet numbers for these systems and Darcys law. Conduction-only conditions should not be expected where specific discharges exceed 10(-8)  m/s. Constraints on hydraulic gradients allow for preliminary screening for advection based on rock or soil types. Identification of materials with very low hydraulic conductivity, such as shale and intact igneous and metamorphic rock, allow for analysis with considering conduction only. Variability in known hydraulic conductivity allows for the possibility of advection in most other rocks and soil types. Further screening relies on refinement of estimates of hydraulic gradients and hydraulic conductivity through site investigations and modeling until the presence or absence of conduction can be confirmed.

Application of an Analytical Solution as a Screening Tool for Sea Water Intrusion

Sea water intrusion into aquifers is problematic in many coastal areas. The physics and chemistry of this issue are complex, and sea water intrusion remains challenging to quantify. Simple assessment tools like analytical models offer advantages of rapid application, but their applicability to field situations is unclear. This study examines the reliability of a popular sharp-interface analytical approach for estimating the extent of sea water in a homogeneous coastal aquifer subjected to pumping and regional flow effects and under steady-state conditions. The analytical model is tested against observations from Canada, the United States, and Australia to assess its utility as an initial approximation of sea water extent for the purposes of rapid groundwater management decision making. The occurrence of sea water intrusion resulting in increased salinity at pumping wells was correctly predicted in approximately 60% of cases. Application of a correction to account for dispersion did not markedly improve the results. Failure of the analytical model to provide correct predictions can be attributed to mismatches between its simplifying assumptions and more complex field settings. The best results occurred where the toe of the salt water wedge is expected to be the closest to the coast under predevelopment conditions. Predictions were the poorest for aquifers where the salt water wedge was expected to extend further inland under predevelopment conditions and was therefore more dispersive prior to pumping. Sharp-interface solutions remain useful tools to screen for the vulnerability of coastal aquifers to sea water intrusion, although the significant sources of uncertainty identified in this study require careful consideration to avoid misinterpreting sharp-interface results.

Preface: Hydrogeology of shallow thermal systems

Hydrogeologyplaysanimportantroleinthetransferofheatin geological systems. Large-scale variations in thepermeabilitydistribution(includingthepresenceoffracturezones and faults) can significantly impact the coupled flowof heat and fluid (Smith and Chapman 1983). At theregional scale, groundwater flow can alter the heatdistribution, depressing or enhancing thermal gradients inspace and time, and carry heat over significant distances(Smith and Chapman 1983; Woodbury and Smith 1985;Molina-Giraldoetal.2011).Atsmallerscales,groundwaterflow can present challenges to the proper design of geo-exchange systems and can limit the success of aquiferthermal energy storage (ATES) and borehole thermalenergy storage (BTES) systems (e.g. Sauty et al. 1982a, b).This special issue of Hydrogeology Journal presents acollection of articles that aim to advance understanding ofcoupledhydrogeologicalandthermalprocessesoverarangeof spatial and temporal scales. The articles are broadlyclassified into three topics including springs (thermal andmineralized), basins (sedimentary and structure controlled),andgeo-exchangesystems.Theissuefocusesonnovelfield-and modeling-based studies that have been carried out tostudytheseshallowthermalsystems,wherehydrogeologicalprocesses play an active role in the redistribution of heat.The decision to focus on shallow thermal systems asopposed to deep thermal systems was driven largely by ajoint interest in highlighting low-to-moderate temperature(enthalpy) geothermal systems. This is not to say that high-temperature systems and/or deep systems are not consid-ered herein, but rather that the emphasis is on lower-temperature systems that are often strongly influenced bygroundwater flow in such a way as to alter the thermalregime, and that tend to exist at relatively shallow depth.Hebig et al. (2012) reviewed some of the early work thatled to definitions of deep groundwater, both from theperspective of flow and geochemical characteristics. Mostof the definitions of deep groundwater point to the absenceof meteoric water (low tritium and a lack of bicarbonate)and slow circulation rates, but emphasize that the term deepgroundwater is not bound to a defined depth below surface.The authors noted that such deep-lying aquifers havebecome important resources for the production of geother-mal energy and alternative potable water sources, or forrepositories (nuclear waste and CO

The Persistence of Brines in Sedimentary Basins

Brines are commonly found at depth in sedimentary basins. Many of these brines are known to be connate waters that have persisted since the early Paleozoic Era. Yet questions remain about their distribution and mechanisms for retention at depth in the Earth’s crust. Here we demonstrate that there is insufficient topography to drive these dense fluids from the bottom of deep sedimentary basins. Our assessment based on driving force ratio indicates that sedimentary basins with driving force ratio> 1 contain connate waters and frequently host large evaporite deposits. These stagnant conditions appear to be relatively stable over geological time and insensitive to factors such as glaciations, erosion, compaction, and hydrocarbon generation. Plain Language Summary Brines that are millions of years old are present at the bottom of many sedimentary basins. Regional groundwater flow should have flushed these brines out of these systems if not for the presence of some trapping mechanism. Here we demonstrate that there is insufficient topography to drive dense brines out of the bottom of many deep sedimentary basins. We provide geochemical evidence that brines within these basins originated as ancient seawater that was trapped during deposition of the sediments in these basins. Our findings may have applications in determining where stagnant groundwaters are present in sedimentary basins.

Insights into contaminant transport from unconventional oil and gas developments from analog system analysis of methane-bearing thermal springs in the northern Canadian Rocky Mountains

Natural gas is currently being produced from shales of the Montney and Liard basins in western Canada. Production requires hydraulic fracturing due to the low permeability of the shales in the basins. Stratigraphically equivalent shales are present in the northern Canadian Rocky Mountains. Thermal springs with notable hydrocarbon concentrations occur where large-scale faults intersect the same shale units that are the focus of gas development, indicating that under certain circumstances, connection of deep fractured shales to the land surface is possible. To constrain these conditions, simulations were conducted for the spring with the highest hydrocarbon flux (Toad River Spring), results of which indicate that in order to supply sufficient water to a fault to support measurable advection, the effective permeability of the shales in these structurally deformed areas must be one to four orders of magnitude higher than in areas of active gas production to the east. The spatial scale of enhanced permeability is much greater than that which is achieved by hydraulic fracturing and the mechanism of maintaining high pressures at depth is more persistent in time. Examination of groundwater velocities suggests that upward migration of solutes from hydraulic fracturing may take decades to centuries. Results also indicate that any temperature anomaly will be associated with transport along a fault at such velocities. No such temperature anomaly has been documented in regions with unconventional oil and gas development to date. Such an anomaly would be diagnostic of a deep solute source.RésuméLe gaz naturel est. actuellement produit à partir des schistes des bassins de Montney et de Liard dans l’ouest du Canada. La production nécessité une fracturation hydraulique en raison de la faible perméabilité des schistes dans les bassins. Des schistes stratigraphiquement équivalents sont présents dans le nord des Rocheuses canadiennes. Des sources thermales avec des concentrations d’hydrocarbures notables se manifestent lorsque des failles de grande échelle recoupent les mêmes unités de schistes qui permettent une mise en valeur par l’exploitation du gaz, ce qui indique que, dans certaines conditions, la connexion des schistes fracturés en profondeur à la surface est. possible. Pour contraindre ces conditions, des simulations ont été réalisées pour la source avec un flux d’hydrocarbure le plus élevé (Source de la Rivière Toad), dont les résultats indiquent que, pour fournir suffisamment d’eau à une faille permettant la mesure d’advection, la perméabilité efficace des schistes dans ces zones déformées structurellement doit être d’un à quatre ordres de grandeur supérieurs aux zones de production active de gaz situées à l’est. L’échelle spatiale de la perméabilité améliorée est. beaucoup plus grande que celle obtenue par fracturation hydraulique et le mécanisme du maintien de fortes pressions en profondeur est. plus durable dans le temps. L’examen des vitesses des eaux souterraines suggère que la migration ascendante des solutés à partir de la fracturation hydraulique peut prendre des dizaines à centaines d’années. Les résultats indiquent également que toute anomalie de température sera associées au transport le long de faille à de telles vitesses. Aucune anomalie de température n’a été documentée dans des régions avec des exploitations de pétrole et gaz non conventionnels à ce jour. Une telle anomalie traduirait la présence d’une source profonde de soluté.ResumenActualmente se está produciendo gas natural a partir de esquistos en las cuencas de Montney y de Liard en el Canadá occidental. La producción requiere la fracturación hidráulica debido a la baja permeabilidad de los esquistos en las cuencas. Los esquistos estratigráficamente equivalentes están presentes en las Canadian Rocky Mountains. Los manantiales termales con concentraciones notables de hidrocarburos ocurren donde las fallas a gran escala intersectan las mismas unidades de esquistos que son el foco del desarrollo del gas, indicando que, bajo ciertas circunstancias, es posible la conexión de los esquistos fracturados profundos con la superficie terrestre. Para limitar estas condiciones, se realizaron simulaciones para el manantial con el mayor flujo de hidrocarburos (Toad River Spring). Los resultados indican que, para suministrar suficiente agua a una falla para soportar una advección medible, la permeabilidad efectiva de los esquistos en estas estructuras en las áreas deformadas deben ser de uno a cuatro órdenes de magnitud más altas que en áreas de producción de gas activo situadas hacia el este. La escala espacial de permeabilidad mejorada es mucho mayor que la que se logra mediante fracturación hidráulica y el mecanismo de mantener altas presiones en profundidad es más persistente en el tiempo. El examen de las velocidades de las aguas subterráneas sugiere que la migración hacia arriba de los solutos a partir de la fracturación hidráulica puede llevar décadas hasta siglos. Los resultados también indican que cualquier anomalía de temperatura se asociará con el transporte a lo largo de una falla a tales velocidades. No se ha documentado tal anomalía de temperatura en regiones con desarrollo no convencional de petróleo y gas hasta la fecha. Tal anomalía sería el diagnóstico de una fuente profunda de soluto.摘要在加拿大西部,目前天然气从Montney 流域和 Liard 流域页岩中开采。由于流域中页岩透水性低,生产需要水力压裂。加拿大境内落基山脉北部存在着地层学上等同的页岩。发现有含相当浓度碳氢化合物的热泉,这里大规模的断层横断相同的页岩单元,而这里的页岩是天然气开采的焦点,表明在一定情况下,深层断裂的页岩与地表的相连是可能的。为了约束这些条件,对具有最高的碳水化合物通量的泉(Toad River泉)进行了模拟,结果表明,为了向断层提供足够的水以支持可测量的平流,这些构造上变形区的有效透水性必须高于东边天然气活跃生产区一到四个数量级。增强的透水性空间尺度大大高于水力压裂取得的空间尺度,保持深部高压的机理时间上更持久。地下水速度测试表明,溶质从水力压裂向上迁移可能需要数十年到几百年。结果还表明,任何的温度异常和如此速度下沿断裂的运移相关联。至今在非常规油气开发地区没有这样的温度异常记录。这样的异常将被认为存在着深部溶质源。ResumoGás natural está atualmente sendo produzido nos folhelhos de Montney e Bacia Liard no oeste do Canadá. A produção requere fraturamento hidráulico devido a baixa permeabilidade dos folhelhos nas bacias. Folhelhos estratigraficamente equivalentes estão presentes no norte das Montanhas Rochosas. Fontes termais com notáveis concentrações de hidrocarboneto ocorrem onde falhas de grande escala interceptam as mesmas unidades de folhelhos que são o foco da produção de gás, indicando que sob certas condições, a conexão dos folhelhos fraturados em profundidade com a superfície é possível. Para delinear essas condições foram conduzidas simulações para a fonte com maior fluxo de hidrocarboneto (nascente do Rio Toad), resultados quais indicam que para fornecer água suficiente para a falha sustentar advecção mensurável, a permeabilidade efetiva dos folhelhos nessas áreas estruturalmente deformadas deve ser de uma ordem de magnitude de uma até quatro vezes maior do que em áreas de produção de gás ativas a leste. A escala espacial da permeabilidade aumentada é muito maior do que aquela alcançada por fraturamento hidráulico e o mecanismo de manter as altas pressões em profundidade é mais contínuo no tempo. Observações das velocidades da água subterrânea sugerem que migração vertical de solutos para cima do fraturamento hidráulico pode levar de décadas a séculos. Resultados também indicam que qualquer anomalia de temperatura será associada com o transporte ao longo de uma falha nessas velocidades. Nenhuma anomalia de temperatura tem sido documentada em regiões com produção de fontes não convencionais de petróleo e gás até agora. Este tipo de anomalia seria um diagnóstico de uma fonte de soluto em profundidade.

Salt dissolution and permeability in the Western Canada Sedimentary Basin

Extensive dissolution of evaporites has occurred in the Williston Basin, Canada, but it is unclear what effect this has had on bulk permeability. The bulk of this dissolution has occurred from the Prairie Evaporite Formation, which is predominantly halite and potash. However, minor evaporite beds and porosity infilling have also been removed from the overlying Dawson Bay and Souris River formations, which are predominantly carbonates. This study examines whether permeability values in the Dawson Bay and Souris River formations have been affected by dissolution, by analyzing 142 drillstem tests from those formations. For both the Dawson Bay and Souris River formations, the highest permeabilities were found in areas where halite dissolution had occurred. However, the mean permeabilities were not statistically different in areas of halite dissolution compared to those containing connate water. Subsequent precipitation of anhydrite is known to have clogged pore spaces and fractures in some instances. Geochemical relationships found here support this idea but there is no statistically significant relationship between anhydrite saturation and permeability. Geomechanical effects, notably closure of fractures due to collapse, could be a mitigating factor. The results indicate that coupling dissolution and precipitation to changes in permeability in regional flow models remains a significant challenge.RésuméUne dissolution d’évaporites de grande envergure s’est produite dans le Bassin de Williston, au Canada, mais son incidence sur la perméabilité en général n’est pas évidente. La majeure partie de la dissolution a eu lieu à partir de la Formation Evaporitique Prairie qui est à dominante de halite et de sylvinite. Cependant, des petits lits d’évaporite et un remplissage de la porosité ont aussi été exportés depuis les formations surincombantes de Dawson Bay et de Souris River qui sont à dominante carbonatée. La présente étude examine si les valeurs de perméabilité dans les formations de Dawson Bay et de Souris River ont été affectées par la dissolution, grâce à l’analyse de 142 essais aux tiges pratiquées dans ces formations. Pour la formation de Dawson Bay comme pour celle de Souris River, les perméabilités les plus élevées ont été rencontrées dans les zones où a eu lieu la dissolution de halite. Cependant, les perméabilités moyennes n’ont pas été statistiquement différentes dans les zones de dissolution de la halite et dans celles contenant de l’eau connée. La précipitation ultérieure de l’anhydrite est reconnue pour avoir fermé des espaces poreux et dans quelques cas des fractures. Les relations géochimiques rencontrées ici confortent cette idée mais il n’y a pas de relation statistiquement significative entre la saturation de l’anhydrite et la perméabilité. Les effets géo-mécaniques, notamment la fermeture des fractures par affaissement, pourrait avoir été un facteur d’atténuation. Ces résultats montrent que le couplage de la dissolution et de la précipitation en vue de modifications de la perméabilité dans les modèles d’écoulement régionaux reste un défi de taille.ResumenSe ha producido una amplia disolución de evaporitas en la cuenca de Williston, Canadá, pero no está claro qué efecto ha tenido ello sobre la permeabilidad global. La mayor parte de esta disolución se produjo a partir de la Formación Prairie Evaporite, que es predominantemente halita y carbonato de potasio. Sin embargo, también se han eliminado capas menores de evaporita y rellenos de la porosidad de las formaciones suprayacentes de Dawson Bay y Souris River, que son predominantemente carbonáticas. Este estudio examina si los valores de la permeabilidad en las formaciones Dawson Bay y Souris River se han visto afectados por la disolución, mediante el análisis de 142 pruebas de barras de perforación de esas formaciones. Para las formaciones Dawson Bay y Souris River, las permeabilidades más altas se encontraron en áreas donde se había producido la disolución de halita. Sin embargo, las permeabilidades promedio no fueron estadísticamente diferentes en las áreas de disolución de halita en comparación con las que contienen agua connata. Se sabe que la precipitación posterior de anhidrita ha obstruido en algunos casos espacios de poros y fracturas. Las relaciones geoquímicas encontradas aquí respaldan esta idea, pero no existe una relación estadísticamente significativa entre la saturación de la anhidrita y la permeabilidad. Los efectos geomecánicos, especialmente el cierre de fracturas debido al colapso, podrían ser un factor atenuante. Los resultados indican que el acoplamiento de la disolución y la precipitación a los cambios en la permeabilidad en los modelos de flujo regionales sigue siendo un desafío significativo.摘要在加拿大Williston盆地,蒸发岩大量溶解,但不清楚溶解对体积平均渗透性有什么样的影响。大多数溶解出现在大草原蒸发岩地层,蒸发岩地层猪油是岩盐和碳酸钾。然而,小的蒸发岩层和孔隙填充物也被从上覆的、主要为碳酸盐的Dawson Bay 和 Souris River 地层中溶解出。通过分析Dawson Bay 和 Souris River 地层142个钻杆试验结果,本研究检查了Dawson Bay 和 Souris River地层渗透性值是否受到了溶解的影响。发现Dawson Bay 地层和 Souris River地层渗透性最高的地方就在岩盐溶解的地方。然而,在岩盐溶解的地方,相比于包含原生水的地方,平均渗透性统计上并没有什么不同。在某些情况下,随后的硬石膏沉淀会堵塞孔隙空间和断裂。发现这里的地球化学关系支持整个观点,但在硬石膏饱和和渗透性之间没有统计学上的重大的关系。岩土力学影响,即,由于崩塌造成的断裂明显闭合可能是一个缓解因素。结果表明,在区域水流模型中,溶解和沉淀对渗透性的变化仍然是一个重要的挑战。ResumoVasta dissolução de evaporitos têm ocorrido na Bacia Williston, Canadá, entretanto não está claro qual o efeito gerado na permeabilidade total. Grande parte dessa dissolução tem ocorrido a partir da Formação Evaporítica das Prairies, predominantemente composta for halita e potassa. Entretanto, camadas evaporíticas menos pronunciadas e preenchimento de porosidade também têm sido removidas a partir das formações Dowson Bay e Souris River sobrejacentes, compostas predominantemente por carbonatos. Este estudo examina se as permeabilidades das formações Dowson Bay e Souris River têm sido afetadas pela dissolução através da análise de 142 testes drillstem destas formações. Para ambas as formações, as maiores permeabilidades foram encontradas em áreas de ocorrência de dissolução de halita. Entretanto, as permeabilidades médias não se apresentaram estatísticamente diferentes em áreas de dissolução de halita comparadas com áreas contendo água conata. Precipitação subsequente de anidrita é reconhecida por ter colmatado poros e fraturas em alguns casos. As relações geoquímicas aqui encontradas corroboram com essa evidência, porém não há relação estatisticamente significativa entre a saturação de anidrita e a permeabilidade. Efeitos geomecânicos, notavelmente o fechamento de fraturas por colapso, podem configurar um fator de atenuação. Os resultados indicam que a articulação de dissolução e precipitação em relação às variações de permebilidade em modelos de fluxo regionais permanece um desafio significativo.