Flowing fluid electrical conductivity logging of a deep borehole during and following drilling: estimation of transmissivity, water salinity and hydraulic head of conductive zones

Abstract

Flowing fluid electrical conductivity (FFEC) logging is a hydrogeologic testing method that is usually conducted in an existing borehole. However, for the 2,500-m deep COSC-1 borehole, drilled at Åre, central Sweden, it was done within the drilling period during a scheduled 1-day break, thus having a negligible impact on the drilling schedule, yet providing important information on depths of hydraulically conductive zones and their transmissivities and salinities. This paper presents a reanalysis of this set of data together with a new FFEC logging data set obtained soon after drilling was completed, also over a period of 1 day, but with a different pumping rate and water-level drawdown. Their joint analysis not only results in better estimates of transmissivity and salinity in the conducting fractures intercepted by the borehole, but also yields the hydraulic head values of these fractures, an important piece of infor-mation for the understanding of hydraulic structure of the subsurface. Two additional FFEC logging tests were done about 1 year later, and are used to confirm and refine this analysis. Results show that from 250 to 2,000 m depths, there are seven distinct hydraulically conductive zones with different hydraulic heads and low transmissivity values. For the final test, conducted with a much smaller water-level drawdown, inflow ceased from some of the conductive zones, confirming that their hydraulic heads are below the hydraulic head measured in the wellbore under non-pumped spaceconditions. The challenges accompanying 1-day FFEC log-ging are summarized, along with lessons learned in address-ing them.

Core‐Log‐Seismic Integration in Metamorphic Rocks and Its Implication for the Regional Geology: A Case Study for the ICDP Drilling Project COSC‐1, Sweden

“…(2017) which are 100 times lower at this depth than at all other depths (overview of logs for the entire borehole in the Figure ). This could be caused by fluid‐filled fractures as evidenced by inflow of water at this depth (Doughty et al., 2017). There are no indications that the mylonite sequences (at about 2,250–2,500 m), described by Lorenz et al.…”

Crystalline Disposal R&D at LBNL: FY20 Progress Report

“…Crystalline Disposal R&D at LBNL: FY20 Progress Report x June 18, (Tsang et al, 2016;Doughty et al, 2017). There is a good correspondence of anomalies observed by the two methods.…”

“…Step-rate Injection Method for Fracture In-situ Properties (SIMFIP) tool, was installed in the borehole COSC-1 for real-time measurements of 3D mechanical displacements within borehole intervals, containing one or more fractures, together with measurements of the injection water flow rate, pressure, temperature and water electrical resistivity. Our team previously used Flowing Fluid Electrical Conductivity (FFEC) logging to identify hydrologically transmissive fractures in this borehole (e.g., Tsang et al, 2016;Doughty et al, 2017) and to link the identified flow zones with fractures observed on the image logs and core samples. The transmissive zones that were identified by the FFEC logs are quite extensive (over 1 m long) in many cases, and there are multiple fracture/foliation features that may correspond to the inflow zones.…”

DISOLV: A Python Package for the Interpretation of Borehole Dilution Tests

“…Borehole flow logging techniques (e.g., Tsang et al 1990;Paillet 1998;Williams and Paillet 2002;Brainerd and Robbins 2004;Doughty and Tsang 2005;Coleman et al 2015) can be used to locate productive fractures and their flow properties. Among these techniques, the single borehole dilution test (SBDT) has been successfully applied to characterize the vertical distribution of aquifer hydraulic properties (e.g., Ward et al 1998;Tsang and Doughty 2003;Williams et al 2006;Pitrak et al 2007;West and Odling 2007;Maurice et al 2012;Doughty et al 2017;Parker et al 2018), to help find fracture depths for packer tests (e.g., West and Odling 2007;Sorensen et al 2013), and to establish the origin of sampled groundwater for chemical analysis (e.g., Sorensen et al 2015). The SBTD is less expensive and time consuming than other often-used traditional methods of aquifer characterization such as pumping tests, slug tests and packer tests.…”

“…The SBDT technique involves injecting a tracer (generally a saline solution) in the open or screened section of a borehole and then measuring the dilution of the tracer with time at different depths. A variant of the SBDT is the fluid flow electrical conductivity (FFEC) logging method (Tsang et al 1990;Doughty and Tsang 2005;Doughty et al 2008Doughty et al , 2017Tsang et al 2016). With this technique, the water in the borehole is initially replaced with deionized water, and then the electrical conductivity profile of the fluid in the borehole is monitored while the borehole is pumped at a constant rate.…”