Models and Interpretation Methods for Single-Hole Flowmeter Experiments

Subsurface and groundwater flow characterization is of great importance for various environmental applications, such as the dispersion of contaminants and their remediation. For single-hole flowmeter measurements, key characteristics, such as wellbore storage, skin factor heterogeneities, and variable pumping and aquifer flow rates, have a strong impact on the system characterization, whereas they are not fully considered in existing models and interpretation methods. In this study, we develop a new semi-analytical solution that considers all these characteristics in a physics-based consistent manner. We also present two new interpretation methods, the Double Flowmeter Test with Transient Flow rate (DFTTF) and the Transient Flow rate Flowmeter Test (TFFT), for interpreting data collected during single and multiple pumping tests, respectively. These solution and methods are used as follows. (i) The impact of wellbore storage, transient pumping rate, and property heterogeneities on the interpretation of data collected during single pumping tests are studied over 49 two-aquifer cases. (ii) The effect of the skin factor heterogeneity on transmissivity and storativity estimates, as well as the variability range of the (non-unique) corresponding solutions, are analyzed for the interpretation of multiple-pumping experiments. The results presented in this work show the importance of the various properties and processes that are considered, and the need for the new models and methods that are provided

A New Cell for Electrical Conductivity Measurement on Saturated Samples at Upper Crust Conditions

International audienceElectrical resistivity soundings are used by geophysicists to determine the structure and composition of the Earth's crust and mantle and to explore natural resources (ore, oil, gas, water). Their interpretations in terms of composition and in-situ physical conditions depend mainly on laboratory measurements of electrical conductivity of rocks at simulated crustal conditions of temperature, pressure, saturation and pore pressures. These measurements present a numbers of limitations, in particular, in the case where conductive pore fluids are present, as in the case of deep reservoir conditions, where temperature exceeds 250 A degrees C. Here, we present a new cell capable of measuring electrical conductivity of large saturated samples at confining pressure up to 200 MPa, pore pressure up to 50 MPa, and temperature up to 500 A degrees C. The measurement cell has been developed in a commercial, internally heated, gas pressure apparatus (Paterson press). It is based on the concept of "guard ring" electrode, which is adapted to samples that are jacketed by a very conductive, metallic material. Numerical modeling of the current flow in the electrical cell allowed defining the optimal cell geometry. Calibration tests have been performed on Fontainebleau sandstones saturated with electrolytes of different conductivities, up to 350 A degrees C. The resulting electrical formation factor and temperature dependence of electrical conductivity are in very good agreement with previous studies. This new cell will improve the exploration and exploitation of deep fluid reservoirs, as in unconventional, high enthalpy geothermal fields. In particular, the investigations address possible effects of fluid-rock interactions on electrical resistivity of a reservoir host rock

Groundwater flow characterization of an ophiolitic hard-rock aquifer from cross-borehole multi-level hydraulic experiments

International audienceOphiolitic formations play a critical role in the groundwater resource of numerous countries and areas. Previous studies show that the structural heterogeneities of these rocks, coming from the presence of both different lithological units and multi-scale discontinuities, result in complex hydrogeological features that are not well characterized yet. In particular, there is a need for understanding how these heterogeneities impact the hydrodynamic properties of ophiolitic aquifers and the highly variable chemical composition of the water. To this end, we conduct various kinds of pumping experiments between two boreholes 15 m apart in the ophiolitic formation of the Batin (BA1) site in the wadi Tayin massif of the Sultanate of Oman. Cross-borehole open pumping experiments, as well as multi-level pumping and monitoring hydraulic tests, are performed in conductive zones that were identified from temperature and flowmeter data, but also in low-permeability zones requiring to manage very low pumping flow rates. The collected data are interpreted with a model implementing non-integral flow dimension, leakage and time-dependent pumping flow rates. The considered modeling concepts and the estimated hydrogeological properties show that the multi-directional structural heterogeneities of ophiolitic aquifers are key features that must be considered in future hydrogeological models because they drive the hydraulic responses of these systems

Characterizing flow zones in a fractured and karstified limestone aquifer through integrated interpretation of geophysical and hydraulic data

A detailed and integrated geologic–hydraulic–geophysical–geochemical study of groundwater flow in the near-vicinity of a borehole drilled into fractured and karstified limestone demonstrates the power of such an integrated approach in localising and characterising preferential groundwater flow pathways and ambient borehole flow. The study, conducted in the vicinity of a 100-m-deep research borehole on the island of Mallorca, achieves such characterisation on a scale from millimetres to tens of metres in scale. More specifically, it adds single packer and open-hole pumping test interpretations to the results obtained during fluid logging, impeller flowmeter testing, borehole imaging, core descriptions and an innovative fracture analysis. This approach allows the delineation of the main flowing features and showed that such features are directly or indirectly linked to karst phenomena. Understanding this complex flow system is critical for an appropriate assessment of groundwater resources and the design of sustainable groundwater production schemes

CoFIS and TELog: New downhole tools for characterizing dispersion processes in aquifers by single-well injection-withdrawal tracer tests

Contaminant migration in aquifers is one of the most debated issues in hydrogeology, as most experimental results display large deviations from the standard (asymptotic) Fickian dispersion theories. Multi-scale investigation and high-resolution sensors are required to determine the origin of non-asymptotic dispersion and validate models. For this, a set of multi-scale Single-Well Injection-Withdrawal (SWIW) tracer tests using a new dual-packer probe CoFIS, including a high resolution optical sensor TELog, are presented. When compared to standard techniques such as salinity measurements, it is shown that high-resolution optical measurements allow an improved characterization of the long-lasting non-asymptotic dispersion mechanisms

Modeling Gas Transport in the Shallow Subsurface in Maguelone Field Experiment

In this paper, TOUGH2/EOS7CA model is used to simulate the shallow injection-monitoring experiment carried out at Maguelone, France, during 2012 and 2013. The ultimate objective of the work is to improve our understanding of gas transport in the shallow subsurface as well as to develop and validate the model to monitor it. This work represents first results towards modelling the nitrogen and CO2 injection experiments carried out. The pressure data from the first injection experiments in summer 2012 is used as basis for comparison. Work is presently going on to incorporate the experimental data into the numerical simulation further

Oman Drilling Project, Scientific Drilling in the Samail Ophiolite, Sultanate of Oman: Proceedings of the Oman Drilling Project

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