Pauline N. Mollema

A Natural Analog for a Fractured and Faulted Reservoir in Dolomite: Triassic Sella Group, Northern Italy

We have used outcrops of dolomite exposed in the Triassic Sella Group of the Italian Central Dolomites as an analog for subsurface low-porosity faulted and fractured dolomite reservoirs. The Sella Group was mildly deformed at shallow burial depth (21,000 m) in a tectonic strike-slip regime during the Eocene-Miocene Alpine compression that caused the formation of joints and strike-slip faults. Because the matrix porosity in the dolomites is low (<5%) and poorly connected, joints and faults are essential to connect vugs and to provide permeability. Field observations of the Sella Group explain why many dolomite reservoirs and aquifers in strike-slip/compressive tectonic regimes are intensely jointed when they are mildly deformed. In this type of tectonic regime, in fact, pervasive jointing over a wide area accommodates small strains and is strictly associated with the formation of strike-slip faults. Our observations allow us to recognize different kinds of fault architectures that correspond to different stages of fault development. In addition, theoretical models and microscopic observations were used to estimate the petrophysical properties of the faulted and jointed dolomite. Small-offset faults (offsets up to 30 mm), characterized by en echelon arrays of joints and pockets or seams of breccia up to 10 mm wide, form areas of high permeability (100-3000 md) due to the presence of many joints and high-porosity breccia. Faults with 1-10 m offsets, characterized by a breccia zone (1-2 m in width) and associated with high joint density in the wall-rock, contain high-porosity (10%) breccia and represent areas of preferred fluid flow. Large-offset faults with offsets more than 10 m contain a wide zone of low-porosity (<1%) breccia and form potential permeability barriers. The areas adjacent to the intermediate- and large-offset faults have high permeability (100-3000 md) because of high joint densities. An important implication of the way faults develop in dolomite is the consistent relationship between the orientation of joints and faults: the faults strikes differ 15-35° from the strikes of the pervasive joint systems. Joint density also increases four to five times in the proximity of the faults. Such relationships can be used to predict the distribution and orientation of joints and faults in subsurface dolomite reservoirs.

Climate and water budget change of a Mediterranean coastal watershed, Ravenna, Italy

It is generally difficult to quantify exactly the freshwater going in or out of the coastal watersheds along the northern Adriatic Sea because, on one hand, excess water is drained and pumped into the sea to prevent flooding but, on the other hand, water is brought onto the land from far away for irrigation. Fragmentation of water authorities makes it difficult to collect all the necessary information. Climate change and increasing salinization of the coastal aquifers make it imperative, however, to better know the quantities of freshwater involved in these small basins. The water budget of a small coastal agricultural watershed along the Adriatic Sea in Italy (The Quinto Basin near Ravenna) is presented here considering different land uses. The evaporation of open water and the evapotranspiration of wetlands, pine forests, bare soil and irrigated agriculture are calculated based on the Penman–Monteith equation and the Cropwat program. The current water budget is based on average climate data from 1989 to 2008 and drainage and irrigation data. Predictions for future evapotranspiration, net irrigation and hydrologic deficit are calculated with climate data from IPCC (The Fourth Assessment Report (AR4) 200, Climate change 2007). From the study results, the soil type may determine whether or not a crop will need more or less irrigation in the future. Regulations on land use should therefore consider which crop type can be grown on a specific soil type. Water budget analysis in scenarios A1b and A2 both show an increase of water deficits in the summer and an increase of water surplus in the winter. This is explained by the fact that a larger percentage of the rain will fall in winter and not during the growth season. The open water evaporation will decrease under future climate scenarios as a result of increased relative humidity in winter and decreased wind velocity. This may have a positive effect on the water cycle. The current irrigation is very abundant, but has beneficial effects in contrasting soil salinization and saltwater intrusion into the coastal aquifer.

Seasonal dynamic of a shallow freshwater lens due to irrigation in the coastal plain of Ravenna, Italy

Irrigation in low-lying coastal plains may enhance the formation of fresh groundwater lenses, which counteract salinization of groundwater and soil. This study presents seasonal dynamics of such a freshwater lens and discusses its influence on the salinity distribution of the unconfined aquifer in the coastal plain of Ravenna, Italy, combining field observations with numerical modeling (SEAWAT). The lens originates from an irrigation ditch used as a water reservoir for spray irrigation. The geometry of the freshwater lens shows seasonal differences because of freshwater infiltration during the irrigation season and upconing of deeper saltwater for the remainder of the year. The extent of the freshwater lens is controlled by the presence of nearby drainage ditches. Irrigation also results in a temperature anomaly in the aquifer because of the infiltration of warm water during the irrigation season. The surficial zone in the vicinity of the irrigation ditch is increased considerably in thickness. Finally, different irrigation alternatives and the influence of sea-level rise are simulated. This shows that it is necessary to integrate irrigation planning into the water management strategy of the coastal zone to have maximum benefits for freshening of the aquifer and to make optimal use of the existing infrastructure.RésuméL’irrigation dans les basses plaines côtières est susceptible de favoriser la formation de lentilles d’eaudouce, qui s’opposent à la salinisation de l’eau souterraine et des sols. Cette étude présente ladynamique saisonnière d’une telle lentille d’eau douce et discute de son influence sur la distribution desalinité dans l’aquifère à nappe libre de la plaine côtière de Ravenne en Italie, combinant desobservations de terrain avec une modélisation numérique (SEAWAT). La lentille provient d’un fosséd’irrigation utilisé comme réservoir d’eau pour l’irrigation par aspersion. La géométrie de la lentilled’eau douce montre des différences saisonnières à cause de l’infiltration d’eau douce durant la saisond’irrigation et des remontées d’eau salées pendant le reste de l’année. L’extension de la lentille d’eaudouce est contrôlée par la présence des fossés voisins. L’irrigation a aussi comme conséquence uneanomalie thermique dans l’aquifère du fait de l’infiltration d’eau à température ambiante pendant lasaison d’irrigation. L’épaisseur de la zone superficielle augmente considérablement au voisinage dufosse d’irrigation Enfin, diverses alternatives d’irrigation et l’influence de l’augmentation du niveau dela mer sont simulées. Elles montrent que l’intégration d’un schéma d’irrigation dans la stratégie degestion de l’eau en zone côtière est nécessaire pour obtenir les avantages maximum pour adoucir lanappe et faire une utilisation optimale de l’infrastructure existante.ResumenLa irrigación en planicies costeras bajas puede favorecer la formación de lentes de agua subterráneadulce, las cuales contrarrestan la salinización del agua subterránea y del suelo. Este estudio presenta ladinámica estacional de una de tales lentes de agua dulce y discute su influencia en la distribución de lasalinidad del acuífero no confinado en la planicie costera de Ravenna, Italia, combinandoobservaciones de campo con modelado numerico (SEAWAT). La lente se origina a partir de unaacequia usada como un reservorio de agua para la irrigación por aspersión. La geometría de la lente deagua dulce muestra diferencias estacionales debido a que la infiltración de agua dulce durante de laestación de irrigación y el desplazamiento vertical de agua salina más profunda durante el resto delaño. La extensión de la lente de agua dulce está controlada por la presencia de acequias de drenajecercanas. La irrigación también produce una anomalía en la temperatura del acuífero debido a lainfiltración de agua cálida durante la estación de irrigación. La zona superficial en la vecindad de laacequia de irrigación incrementa considerablemente su espesor. Finalmente, se simulan las diferentesalternativas de irrigación y la influencia del ascenso del nivel del mar. Esto muestra que la integraciónde la planificación de la irrigación dentro de la estrategia de manejo del agua de la zona costera esnecesaria para obtener los máximos beneficios y para proveer de agua dulce al acuífero y hacer un usoóptimo de la infraestructura existente.摘要低洼沿海平原灌溉可增加地下淡水透镜体的形成, 从而抵消地下水和土壤的盐度。结合野外观测和数值模拟, 本研究展示了这样的淡水透镜体的季节性动态变化, 论述了淡水透镜体对意大利Ravenna (拉文那) 沿海平原非承压含水层盐度分布的影响。透镜体源自作为喷灌储水池的灌溉渠沟。由于灌溉期间的淡水渗透及其他时间内出现的深部咸水倒锥, 透镜体的几何结构显示出季节性差异。淡水透镜体的范围受附近排水沟的控制。由于灌溉季节温水的渗透, 灌溉也导致含水层温度异常。灌溉沟渠附近的表层带厚度增加非常大。最后, 模拟了不同的灌溉替代选择及海平面上升的影响。表明, 有必要制定综合的沿海地区水管理战略灌溉规划, 以获取含水层淡化的最 大效益及优化利用现有的基础设施。ResumoA rega em planícies costeiras de zonas baixas pode induzir a formação de lentes de água doce queimpedem a salinização da água subterrânea e do solo. Este estudo apresenta a dinâmica sazonal deuma destas lentes de água doce e analisa a sua influência na distribuição da salinidade do aquíferofreático na planície costeira de Ravenna, Itália, combinando campos de observação com modelaçãomatemática (SEAWAT). A lente forma-se a partir de um açude que é usado como reservatório de águapara rega por aspersão. A geometria da lente de água doce mostra diferenças sazonais devido àinfiltração de água doce durante o período de rega e ascensão de água salgada mais profunda durante oresto do ano. A dimensão da lente de água doce é controlada pela presença de valas de drenagempróximas. A rega também induz uma anomalia de temperatura no aquífero devido à infiltração de águaquente durante o período de rega. A zona superficial nas proximidades do açude de rega aumentousignificativamente de espessura. Finalmente, foram simuladas alternativas distintas de rega e ainfluência do aumento do nível do mar. Isto demonstra que a integração do planeamento da rega noâmbito da estratégia de gestão de água da zona costeira é necessária para obter o máximo rendimentoda introdução de água doce no aquífero e para fazer o melhor uso da infraestrutura existente.

Irrigation Management in Coastal Zones to Prevent Soil and Groundwater Salinization

Soil salinization is one of the most widespread soil degradation processes on earth and, worldwide, one billion hectares are affected, mainly in the arid–semiarid regions of Asia, Australia and South America [1]. In Europe, soil salinity has effects on one million hectares mainly in the Mediterranean countries [1]. There are two types of salinization: primary salinization caused by natural events such as sea spray or rock weathering or seepage [2] and secondary salinization that is caused by human activities such as irrigation with salty water, groundwater overexploitation and excessive drainage [1].

Fracture patterns and fault development in the pelagic limestones of the Monte Conero Anticline (Italy)

Fracture patterns reflect the tectonic history of an area. By studying the characteristics of fracture patterns in outcrops it is feasible to reconstruct the sequence of events which helps to predict the fracture patterns in similar geological settings including fractured reservoirs and aquifers. This paper studies the fracture assemblages exposed in outcrops of the Monte Conero anticline, formed by two principal carbonate formations: the Maiolica and the Scaglia Rossa.Fieldwork measurements of fracture properties such as, orientation, length, aperture, microscope analysis of thin sections and crosscutting relationships, led to the recognition of a sequence of events and a fault development model that can explain the occurrence and morphology of breccia zones. The fractures occurring in the outcrops of Monte Conero, consist of veins, stylolites, joints, faults with breccias that occur both in elongated zones and in pockets. Veins and stylolites are the most occurring fractures and the highest fracture density occurs in outcrops along the coastline. Veins and stylolites are arranged in various geometries (e.g. en-echelon) which influence the connectivity with other fractures. Veins and stylolites play a fundamental role in the fault development process. Maiolica and Scaglia Rossa Fm. show different processes of fault development. The initial phase of fault development consists in both formations by shearing along pre-existing veins and the connection of veins by tail-joints.These tail joints break up the rock in between overlapping segments of sheared veins. In the Maiolica Fm, both joints and stylolites form at the tip of faults. The discontinuities at the tip of the faults are explained by high local stress concentrations. The relationships between fracture types observed at the micro-scale are similar to the ones observed at the outcrop-scale. Three different geological episodes were identified and each one is associated to a rotation of the directions of the principal stresses, the first episode formed a set of veins at high angle to bedding, the second episode formed sets of stylolites and the third episode caused slip along the pre-existing veins with formation of new sets of veins, stylolites, and breccia. The fault development process in Monte Conero is related to large and local scale tectonic events during which the veins, stylolites, joints and faults were formed and connected at different stages of the folding process, generating breccia zones. Breccia zones in faults are the only structures that contribute substantially to the secondary porosity of the low-porosity Coneros carbonate rocks.

Application of analytical diffusion models to outcrop observations: Implications for mass transport by fluid flow through fractures

A pavement outcrop with excellent exposure of spatial relationships among joints, veins, small offset normal faults, and associated alteration halos (redox fronts) provided an opportunity to compare predictions of analytical models for reaction front propagation in a fracture-matrix system with a real-field situation. The results have important implications for fluid flow and pollutant transport through a fractured medium. The alteration halos observed suggest that all joints of different sets and most small faults are conductive to meteoric water at shallow depth. On the other hand, veins are local barriers to mass transport by diffusion. By using petrologic and petrophysical data, analytical modeling, and the width of the alteration halos, it was possible to estimate when the fracture network was open to fluid flow. The inferred time for fluid flow and diffusion through the fracture network is sensitive to the porosity n of the rock matrix used in the analytical solutions: 2200 ± 500 years with n = 0.08, 4600 ± 900 years with n = 0.05, and 16,000 ± 4000 with n = 0.02. The second and third age determinations are consistent with the landscape evolution of the area since the end of the last Wűrmian ice age and with the timing required to fill the fractures observed in outcrop. We suggest that analytical modeling is an important tool for the determination of transport and reaction time scales in fractured formations where it is constrained by a robust petrophysical and chemical properties data set.