Hytool: an open source matlab toolbox for the interpretation of hydraulic tests using analytical solutions

Abstract

SummaryHydraulic tests are hydrogeological field experiments used to identify aquifer types and physical parameters. They consist of applying a hydraulic perturbation such as pumping groundwater in a well and observing the variations of the groundwater levels in the same well or in other observation wells. Many types of tests, involving different types of hydraulic perturbations, and many analytical solutions, have been developed in the past to interpret such experiments (Raghavan 1993) (P. Renard 2006).Hytool is a Matlab toolbox that provides a catalog of classical analytical solutions for interpreting hydraulic tests. It includes models corresponding to different flow conditions and aquifer types (confined aquifers, unconfined aquifers, double-porosity media, general radial flow, single fracture, fractal media). Some solutions for multiple pumping rates, constant head test, or slug tests are available as well as bounded aquifers.The structure of the code is modular and allows a user to easily add new solutions when needed. Often the solutions are expressed as dimensionless equations in the Laplace domain. Therefore, the code structure includes an implementation of the Stefhest (Stehfest 1970) and de Hoog techniques to invert numerically the Laplace transform.In addition to the analytical solution, hytool contains a set of functions to help the user load and manipulate the hydraulic test data, construct diagnostic plots (P. Renard, Glenz, and Mejias 2009), fit automatically a model, and report the results as illustrated in the following figure. In this example, a data set (measurements of groundwater drawdown as a function of time during a constant rate pumping experiment) is interpreted using the Theis analytical model. The graph shows the superposition of the data and the model and includes the logarithmic derivative of the data and model. Below the graph, hytool provides information about the parameters that were obtained by the least-square procedure, the quality of the fit and the values of the hydraulic properties of the aquifer (transmissivity and specific storage).The user documentation is included within the toolbox and available as internal help within Matlab. The help contains a description of each individual function plus a series of examples including data sets that are used to demonstrate how hytool can be used in practice.Hytool is employed for teaching purposes in the University of Neuchâtel. It is also used in several research projects for determining the hydraulic properties of porous or fractured (Mejías, Renard, and Glenz 2009) aquifers. This often constitutes a preliminary step for many hydrogeological applications. Hytool was for example used in the context of estimating groundwater inflows in tunnels (Dematteis et al. 2003) or groundwater modeling study (Alcolea et al. 2009). Recently, Hytool was used in a research project devoted to the development of a new geophysical monitoring method (DesRoches and Butler 2016).Renard, (2017). Hytool: an open source matlab toolbox for the interpretati...

Fault sealing and caprock integrity for CO<sub>2</sub> storage: an in-situ injection experiment

“…After reaching this "reactivation", we started the long-term CO 2 -saturated fluid injection below the FOP at a constant pressure of 4.5 MPa. An analysis of the decay curve from 4.8 MPa with a Cooper-Neuzil model (Renard, 2017) results in an estimated transmissivity of 9.2×10-12 m2/s, which is more than one order magnitude increase compared to previous estimates (see above). Worth to note that for the estimate, here we considered only the last step and analysed the decay from considering the previous step pressure (i.e.…”

“…The transmissivity of the fault zone was estimated by analysing a pulse test (still performed in interval Q4) with a Cooper-Bredehoeft-Papadopulos-Neuzil model (Cooper at al., 1967;Neuzil, 1982;Renard, 2017). Figure 10a-b showed the pressure variation and the fit with the model that results in a transmissivity of 1.8×10 -13 m 2 /s.…”

“…is obtained by analysing the first step of the LST (Fig. 10c-d) with a Jacob and Lohman model (Renard, 2017). For this model, only the flow rate is used to estimate the transmissivity.…”

Multi-disciplinary characterizations of the Bedretto Lab – a unique underground geoscience research facility

“…3. The analysis of the transient pressure curves was carried out with the MATLAB Toolbox 'hytool' (Renard, 2017). The tests were analyzed with two models, Theis (1935) and Generalized Radial Flow (GRF) (Barker, 1988).…”

Tracking Fluid Flow in Shallow Crustal Fault Zones: 2. Insights From Cross‐Hole Forced Flow Experiments in Damage Zones

“…In this study, we sought the model that best described our data based on temporal onset, scaling, and final amplitude. Model fits to observed pressure transients were obtained by automated least squares fits using the open source Hytool code (Renard, ). The quality of the best fits obtained was assessed using the root‐ mean‐square error (RMSE).…”