Abstract
Distributed temperature sensing is known to provide sharp signals which are very efficient for mapping hydraulically active fractures in wellbores. High-resolution temperature sensing has specifically demonstrated its capacity to characterize very low flows in wellbores. But as sharp as they can be, temperature profiles are often difficult to decipher. The aim of the present work is to provide and to test the “Borehole Heat Budget Calculator” (BHB Calculator), which is implemented as a fast and easy to use tool for the quantitative analysis of depth-temperature profiles. The Calculator is suitable for most pumping and draining configurations, as the heat budget is generalized for modelling multidirectional flow systems within the same wellbore. The formatted worksheet allows the quick exploitation of temperature logs, and is applicable for the characterization of distributed fractures in long screened wellbores. Objectives of the heat modelling are to enhance the readability of complex depth-temperature data, as well as to quantify distribution of inflow intensities and temperatures with depth. The use of heat budget helps to clearly visualize how heat conduction and heat advection contributions are distributed along wellbores profiles. Calculations of inflow temperatures and their evolution through pumping duration is a prerequisite to infer about the nature of aquifer properties (i.e. conduits, distributed or discrete fractures, porous media), as well as to give insight information about the mapping of effective flow paths draining the aquifer. The efficiency and limitations of the BHB Calculator are being tested through high-resolution temperature logging, along with complementary flowmetering and televiewing logging in fractured aquifers located in the St-Lawrence Lowlands, Quebec, Canada.
Highlights
As an omnipresent parameter, temperature can be seen as a “free tracer” in the hydrosphere
Depth-temperature data collected in this study recalled the capacity of the technique to sharply localize water inflows in wellbores. Such profiles collected with a high-resolution thermistor demonstrated tremendous capacity to reveal low flows which remained undetectable with a spinner flowmeter
The Borehole Heat Budget Calculator (BHB Calculator) provided along with this work is dedicated for hydrogeologists who want to enhance the readability and to perform quick quantitative analysis of complex depth-temperature profiles acquired in the context of heterogeneous aquifers
Summary
Temperature can be seen as a “free tracer” in the hydrosphere. The acquisition of temperature data has been amazingly useful since decades for numerous and various applications in Earth sciences, to generally infer about complex fluid-flow patterns within geological environments. Depth-temperature logging has extensively been used in hydrogeology, especially for characterizing complex fracture architecture within bedrock aquifers. Passive measurement with high-resolution thermistors shows great efficiency for mapping hydraulically active fracture distribution and interconnectivity [10] [11], even by coupling temperature and flow metering surveys together [12] [13]. Advances in groundwater flow characterization in a fractured bedrock aquifer appears to be active using optical fiber DTS, efficiency of which is at its best with an “active temperature sensing” mode, involving the use of a heating device in wellbores [14] [15] [16]. Analytical models for inferring CO2 leakage from temperature logging data have been recently published [19]
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