Technical Report NTB 85-08

Hydrogeologic testing of crytalline rocks during the Nagra deep drilling programm

The purpose of this report is to document the theoretical basis and practical application of the NAGRA hydrogeologic testing program. The report deals with borehole hydraulic testing methods and interpretations, commencing with the governing flow equations and their application to various test procedures, such as pulse tests, drill stern tests, pumping tests, etc. The theoretical considerations include quantitative assessment of the relative significance of various fluid properties, equipment compliance, borehole pressure history, thermally induced pressure responses and pressure/temperature skin effects. Practical considerations in the test analyses and interpretation are also quantitatively considered. These considerations include; the flow regime conceptualization (e.g., porous media or fractured media), assumptions inherent in the solutions, estimation of reference pressure, estimation of storage coefficient, pre-test pressure and thermal conditions, borehole diameter, measurement scale, radius of influence, fracture orientations, borehole/formation skin effects, fluid properties, equipment accuracy and resolution, equipment compliance, and test procedures. These considerations are illustrated with numerous examples based on the NAGRA program. The report concludes with detailed guidelines for the measurement of formation pressure. The guidelines are designed to provide a decision-making logic basis for the field hydrogeologists responsible for conducting hydraulic tests.