Work over rig of the United Downs Deep Geothermal Power project while logging and hydraulically testing the well UD-1 in July 2020 (photo by Lucy Cotton, GeoScience Ltd.)
At the United Downs Deep Geothermal Project (UDDGP) demosite the second phase of well logging and testing of the deep well UD-1 (5058 m total vertical depth (TVD), 5275 m measured depth (MD)) was performed in July and August 2020.
This work started with the removal of a temporary downhole packer from UD-1, which was installed after drilling the well. Afterwards several downhole logging operations were performed in cooperation with the MEET partners TUDa, GeoT and ESG. This included a continuous temperature log to validate the temperature prognosis under equilibrium conditions proving a reservoir temperature of about 188°C at 5 km. Furthermore, a calliper log was used to analyse the condition of the open hole section as preparation for the side wall coring. Based on these logs and the more extensive logging data from the initial runs in May 2019 the targets to obtain the deepest side wall cores ever taken in the granitic basement onshore Great-Britain were selected. Targets were defined based on local anomalies of the geothermal gradient, representing in- or outflow zones, of the gamma ray log which helped to identify open or mineralized faults and fractures, mud loss and gas influx zones, which indicated permeable zones as well as on the direct interpretation of the acoustic image log.
With the 40-hour side wall coring operation under challenging conditions, we successfully obtained 19 of the initially planned 30 rock samples in three separate coring runs. Samples were collected from all previously selected target zones including both the promising main fault and fracture corridors, which represent the fractured reservoir, as well as all different varieties of the local granite.
The side wall cores will enable us to study the reservoir rock in much more detail to gain important knowledge on their mineralogy, their hydrothermal alteration, their geochemical composition, their degree of micro-fracturization as well as their thermal, hydraulic and mechanical properties.
This in combination with the currently ongoing hydraulic tests of the well will provide us the understanding needed to design the stimulation of the well, which is planned and conducted until the end of 2020. These stimulation measures are planned to enhance the natural flow rate of the wells to a level which allows for economic, sustainable production of geothermal energy.
MaxCor-Tool from Baker Hughes below the work over rig at UD-1 ready being prepared for taking side wall cores for detailed reservoir rock characterization as part of the MEET project (photo by Lucy Cotton, GeoScience Ltd.)
Deepest side wall core from 4896.7 m MD ever obtained onshore Great Britain from the United Downs project well UD-1 (photo by Lucy Cotton, GeoScience Ltd.)