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Abstract Fracture stimulation (propped or acid) of soft chalk formations typically suffers from a loss of fracture conductivity over time, due to a gradual failure of the fracture face and the production of fines. Diammonium Hydrogen Phosphate, or DAP, has been used for generations by masons and sculptors to produce a surface hardness to carved limestone. Exposure of chalk samples to low concentration solutions of DAP have shown significant increases in the relevant mechanical properties. Until recently this was confined to the laboratory and this paper discusses the progress that has been made with DAP in the Norwegian Sector of the North Sea, up to and including the first field trial. This paper will discuss the underlying laboratory testing performed to establish the effectiveness of this mechanical property improvement and mitigation of any detrimental effects, in order to assess the recommended strength and quantity for use. This testing included simple soak tests, core flow testing, proppant conductivity testing, fluid stability and materials compatibility, as well as additional requirements to qualify this chemistry for use in the Norwegian Sector of the North Sea. Included in this are a suite of yard-based mixing trials, and the qualification and mobilisation of a Platform Supply Vessel (PSV)-based equipment spread to perform the initial treatment. Also included in this paper will be the laboratory testing that demonstrates the improvement in mechanical properties that has been achieved, along with decisions and directional trends that were taken with the chemistry development. Following on from this, the paper will detail preparation and execution of the first field trial performed with the DAP chemistry, into a horizontal lateral already completed with 20 individually propped fractured intervals. The paper will report the considerations that were made, intervention approach that was selected, as well as the manner in which these treatments will be designed. Finally, the execution data will be presented which shows the formation responses. This paper will conclude with the lessons learned from the field trial and recommendations for the continued testing and use of this material. As noted, this treatment is - to the best of the Authors’ knowledge - the first time this material has ever been pumped into an oil or gas well, globally.