HS2 Wendover Green Tunnel

Case Study

HS2 Wendover Green Tunnel – Packer & Geophysical Testing

Client: EKFB
Location: Wendover, Buckinghamshire
Duration: October 2020 – May 2021

Project Overview

As part of a larger scale pumping test on HS2, extensive geophysical logging of two pumping wells was undertaken. Wells were drilled in 146mm Geobore S casing with core recover. After drilling, the Geobore S was removed and open borehole well development was carried out to ensure clear geophysical logging results. Geophysical Logging was undertaken utilising the following logging sondes:

Optical Borehole Imager (OPTV)

A precision machined prism and CCD camera produces a high definition video image which captures and records horizontally and vertically. This is digitised and the image is orientated north facing, to allow for potential structural analysis. To ensure a quality image is produced, OPTV should be adequately centralised in the bore and run in clear water or air. Real-time monitoring is undertaken when logging to ensure quality.

Fluid Temperature and Conductivity

Fluid temperature and conductivity logging was undertaken to establish localised flow regimes within the borehole. Electrical conductivity can establish a measure of the groundwater quality in regards to its ultimate salinity and dissolved solids, logs ultimately aid inflow determination.

Impellor Flowmeter

Impellor logs are utilised to determine any flow patterns within a well and highlights ultimate flow zones. When undertaking logging the winch is ran at a consistent speed to allow for compensation against speed to be undertaken.

Caliper Logging

When drilling in difficult ground conditions, caliper sondes are a perfect resource for identifying washout, faults and voiding. As a quality assurance tool these are perfect to ensure that a well screen has been installed correctly and there are no breaches to the wells integrity. When dewatering they’re perfect for ensuring that vital fractures and fissures are not cut off.

Natural Gamma

Natural gamma logging is a valuable tool for determining formation lithologies. These sondes pickup naturally emitted gamma radiation from clays that contain potassium K40 through to U238 and Th232. When logging, if in lithologies that are higher in concentrations of clays there is more gamma radiation emitted and thus more log movement.

Focused Resistivity Log

Focused resistivity sondes have built in Guard Electronics which project electrical current into rock formations being logged. Our sondes have two spacings on the tool to allow for shallow and deep penetration on the relevant formations. With this testing in combination with the other testing sondes we are able to aid determination of porosity, pore water quality.

Quality & Reporting

Extensive and immediate geophysical analysis was needed as part of the specification. Quick interpretation and analysis of logging results was essential in determining final well installation detail. Thorough and highly detailed logs were produced with detailed information regarding the parameters of all conditions found.