Open-Loop Chalk Wells – London

Project Involvement

Drilling large diameter of chalk wells, carrying our well development and acidisation, undertaking dewatering pumping tests.

Introduction

Project Dewatering Ltd (PDL) was appointed by the client to install and test new chalk wells as part of an open-loop ground source heating and cooling system for the prestigious development in central London. The dewatering system was designed to provide renewable heating and cooling to the property using circulated water from the chalk aquifer of the London Basin.

The Works

As part of the dewatering works, PDL drilled four 130m deep chalk wells using reverse circulation techniques at 500mm diameter. A permanent steel casing of 320mm diameter was installed and sealed into the top of the chalk aquifer at depths of approximately 80m, with the remainder of the borehole left as an open-hole section through the competent chalk.

The reverse circulation well drilling system ensured both increased borehole stability during drilling and improved cuttings removal leading to a better developed final product. Each well was acidised by our specialist borehole development crew by the controlled injection of 5 tonnes of hydrochloric acid into the sealed borehole.

A programme of airlift development pumping and intermittent development pumping was carried out to ensure the wells met strict environmental criteria. Specifically, this resulted in a low level of potential fouling from the abstracted water when passed through a plate heat exchanger and then re-injected back to the aquifer. A groundwater pumping test method included individual step tests, constant rate tests and abstraction-recharge testing on multiple wells.