For clarity, the term “naturally fractured”, referred to in a previous letter to local residents, means nature has created fractures in the rock as it does in many rocks, particularly in limestone, through the stresses, strains and upheavals of being buried underground for millions of years.
For the avoidance of doubt and any differing interpretations of the word intend, Cuadrilla will not be carrying out hydraulic fracturing at the Lower Stumble site now or in the future. Cuadrilla is not engaged in any sale of its interest in the relevant licence for the site. The purpose of flow testing is to measure the rate at which oil would flow from the well. This type of flow testing is regularly and commonly used to assess flow rates and pressures, data which can be used by engineers to estimate the size of the oil accumulation.
To aid this process Cuadrilla proposes to circulate a dilute hydrochloric acid solution (90% water, 10% Hydrochloric acid) along the horizontal length of the wellbore at pressures below the fracture pressure of the surrounding rock. At this dilution ratio the solution is classified as non-hazardous to groundwater.
The purpose is to dissolve and remove any residual drilling mud from the wellbore and clean the face of the limestone rock immediately adjacent to the horizontal well. This will help facilitate the flow of oil from the limestone into the well. This is an entirely safe process frequently used in drilling wells, including in wells intended for water abstraction such as for agricultural and industrial use.
Contrary to an assertion made by some, this is not the same as hydraulic fracturing as the process is not carried out at sufficient pressure to fracture the rock and contains no proppant (typically sand is used in fracturing fluid), as it is not designed to create or prop fractures open.