Influences of hydraulic boundary conditions on the deep fluid flow in a 3D regional model (central Upper Rhine Graben)

Knowledge of groundwater flow is of high relevance for groundwater management or the planning of different subsurface utilizations such as deep geothermal facilities. While numerical models can help to understand the hydrodynamics of the targeted reservoir, their predictive capabilities are limited by the assumptions made in their setup. Among others, the choice of appropriate hydraulic boundary conditions, adopted to represent the regional to local flow dynamics in the simulation run, is of crucial importance for the final modelling result. In this work, we systematically address this problematic in the area of the central part of the Upper Rhine Graben. We quantify how and to which degree different upper boundary conditions and vertical cross-boundary fluid movement influence the calculated deep fluid flow conditions in the area under study. Robust results, which are insensitive to the choice of boundary condition, are: (i) a regional groundwater flow component descending from the graben shoulders to rise at its centre and (ii) the presence of heterogeneous hydraulic potentials at the rift shoulders. Contrarily, results affected by the chosen boundary conditions are: (i) calculated flow velocities, (ii) the absolute position of the upflow axis, and (iii) the evolving local flow dynamics. If, in general, the investigated area is part of a supra-regional flow system—like the central Upper Rhine Graben is part of the entire Upper Rhine Graben—the inflow and outflow across vertical model boundaries need to be considered.

Chihuahua-Sacramento and tabalaopa-aldama aquifers of Chihuahua state, Mexico: linkage and importance of geostatistical and hydrogeochemical analysis

The objective of this study is to gather sufficient information to make a diagnosis of drinking water sufficiency in the Chihuahua-Sacramento and Tabalaopa-Aldama aquifers. By applying advanced statistical techniques, the goal is to find the variables that control the regional and intermediate flow systems and establish the characteristics of a heterogeneous aquifer. The variables chosen from those established were as follows: total solids (TS), nitrates (NO3), fluoride (F), and total hardness, among others. In order to establish a conceptual model, the results from all the sampling were carried out by the National Water Commission (CONAGUA) in the aforementioned aquifers and were used to obtain an approximate flow differentiation. The results showed a good flow differentiation. In addition, a group of mixed water was detected among the intermediate and regional flows. The increase in the average regional flow values suggests a rise in the incidence of an upward flow of the regional flow as a result of uncontrolled extraction.

Conceptualizing the hydrogeothermal setting of Sloquet Hot Springs in the Canadian Cordillera on unceded St'at'imc Territory: an example of a reconciliation-based approach to field geoscience

Field geoscience has made important scientific advances but has not consistently considered the impact of these geoscience results on communities where the fieldwork is conducted. A reconciliation-based approach calls for critical thought about who defines, participates in, owns, and uses geoscience research, particularly in light of unresolved aboriginal rights and title claims and treaty rights throughout all of Canada. Geothermal research in the Canadian Cordillera has typically focused on hot spring systems and predicting maximum temperatures at depth, estimating fluid circulation depths, and investigating the distribution of hot spring systems and their relation to major geological features that often control thermal fluid flow. Detailed fieldwork to develop local and regional conceptual models of these systems has rarely been conducted and to our best knowledge, never in partnership with a First Nation. The scope of this project was working collaboratively with Xa’xtsa First Nation to conduct detailed structural, hydrologic and hydrogeologic fieldwork to develop local and regional conceptual models of Sloquet Hot Springs, on unceded St'at'imc territory. To motivate our research and provide a successful example of a reconciliation-based approach to field geoscience, we review how resource regulation, research, relationships, and reconciliation interact in British Columbia and consider our community partnership relative to Wong et al (2020)’s 10 Calls for Action for Natural Scientists. Well drilling, testing and monitoring revealed numerous soft zones in the subsurface as well as high transmissivity suggesting bedrock in the area has significant permeability. The annual flux calculated for Sloquet Hot Springs suggests a regional flow contribution from nearby watersheds. Although surface and subsurface observations did not identify the primary fault that conveys high-temperature fluids, the potential locations of buried fault structures are hypothesized based on zones with observably high temperatures and flow along Sloquet Creek. These results and interpretations are synthesized into a conceptual model of a localized hydrogeothermal system with local and regional groundwater flow along permeable pathways in the subsurface and mixing with cooler water before discharging in some of the springs.

Numerical Simulation of Heat Transport Problems in Porous Media Coupled with Water Flow Using the Network Method

In the present work, a network model for the numerical resolution of the heat transport problem in porous media coupled with a water flow is presented. Starting from the governing equations, both for 1D and 2D geometries, an equivalent electrical circuit is obtained after their spatial discretization, so that each term or addend of the differential equation is represented by an electrical device: voltage source, capacitor, resistor or voltage-controlled current source. To make this possible, it is necessary to establish an analogy between the real physical variables of the problem and the electrical ones, that is: temperature of the medium and voltage at the nodes of the network model. The resolution of the electrical circuit, by means of the different circuit resolution codes available today, provides, in a fast, simple and precise way, the exact solution of the temperature field in the medium, which is usually represented by abaci with temperature-depth profiles. At the end of the article, a series of applications allow, on the one hand, to verify the precision of the numerical tool by comparison with existing analytical solutions and, on the other, to show the power of calculation and representation of solutions of the network models presented, both for problems in 1D domains, typical of scenarios with vertical flows, and for 2D scenarios with regional flow.

Hydrogeochemical indications of regional flow in the Lower Greensand aquifer of the London Basin

The Lower Greensand (LGS) forms the second most important aquifer in the London Basin but, being largely absent beneath the city itself, has received much less attention than the ubiquitous overlying Chalk aquifer. While the general directions of groundwater flow in the Chalk are well established, there has been much less certainty about flow in the LGS owing to regionally sparse borehole information. This study focuses on two hitherto uncertain aspects of the confined aquifer: the sources of recharge to the west-central London Basin around Slough, and the fate of LGS water where the aquifer thins out on the flank of the London Platform in the Gravesend–Medway–Sheppey area on the southern side of the basin. The application of hydrogeochemical techniques including environmental isotopes indicates that recharge to the Slough area is derived from the northern LGS outcrop, probably supplemented by downward leakage from the Chalk, while upward leakage from the LGS in North Kent is mixing with Chalk water to the extent that some Chalk boreholes on the Isle of Sheppey are abstracting high proportions of water with an LGS fingerprint. In doing so, this study demonstrates the value of re-examining previously published data from a fresh perspective.Thematic collection: This article is part of the Hydrogeology of Sandstone collection available at: https://www.lyellcollection.org/cc/hydrogeology-of-sandstone

Regional flow climatology for central Mexico (Queretaro): a first case study

A flow climatology was established for the Metropolitan Area of Queretaro (MAQ), in central Mexico, by analyzing four years (2014-2017) of back-trajectories generated using the HYSPLIT Model. Two flow regimes were found: one from June until September (rainy regime); the other from December to May (dry regime). October and November were considered transition months. Northeasterly flows were present throughout the year; in contrast, trajectories from the southwest were much less frequent and observed mainly during the dry regime. An analysis of the wind fields from the NARR database for a longer period of time (1979 – 2019), suggests that these results are representative of the average conditions of the atmosphere at the study site. Some of the northeasterly trajectories observed originate within a desertic region of the state of Queretaro, where several limestone mines are located. During the dry regime and transition months some clusters originate at the industrial area in Guanajuato, which includes the Salamanca refinery. As air transport of pollutants follow these paths, this analysis could be useful for identifying regional sources that affect the MAQ and possibly increase its air pollution load. In fact, the variability of criteria pollutants concentrations matched the flow regimes described above.

Hydrocarbon Volume Estimate Using Pseudo Steady-State/Pressure-Transient Principles in a Faulted Reservoir

The application of pseudo-steady-state and pressure transient response techniques to assist in hydrocarbon volume estimate is presented for a reservoir isolated from its main by a non-sealing fault. The techniques discussed in this paper utilized the pseudo steady state principle to determine the fault boundary behavior dominated flow regime of an oil well which has produced for over eight years in a marginal field of the Niger Delta environment. The material balance technique which utilized accountability of fluid withdrawn/injected and energy conservation principles within the pseudo steady state boundary dominated flow was used alongside with the pressure transient analysis to validate this oil in place number. Seismic attributes was also used to predict the geometry and distribution of the sand based on the conventional seismic interpretation. The seismic attribute analyses clearly show the geometry and spatial distribution of the reservoir sand bodies. Hence, understanding a pseudo steady state dominated regional flow time in a faulted reservoir plays a key role in the management and development of reserves in a marginal field operation.