What exists beneath the place where Conrad Schlumberger carried out the first (1912) electrical prospection experiment: the Val‐Richer Abbey. Issue 4 (27th July 2018) - Hulin, Guillaume
ABSTRACT: The Val‐Richer in Normandy is recognised as the place of origin of the resistivity method in applied geophysics. There, during the summer of 1912, Conrad Schlumberger tested for the first time a new method designed to map out the electrical resistivity of the sub‐surface. A well‐known, hand‐drawn blueprint made by Conrad Schlumberger describes this experiment. It shows the voltage distribution observed at the ground surface together with a hand‐written comment describing the difficulties encountered and the solutions retained. This test led the Schlumberger brothers to develop this type of prospection and to later create, first, an engineering office in 1920 and, then, companies among the largest international ones in the oil service industry. In 2014, 102 years after this founding experiment, a research project was initiated with the main objective to delineate the remains of the Val‐Richer Abbey, which were destroyed during the French Revolution. A resistivity survey was conducted complemented by an electromagnetic survey over the area where the abbey's religious buildings were expected to be located, the same place where Conrad Schlumberger's measurements were carried out. The interpretation of the geophysical survey, in the light of archival sources and current knowledge of the Cistercian abbeys of Normandy, has completely altered our previous vision of the Val‐Richer Abbey and made it possible to establish an accurate outline of this monastic settlement. The knowledge about sub‐surface electrical resistivity authorises a renewed analysis of the 1912 blueprint and associated drawings and a new assessment of the solutions then adopted by Conrad Schlumberger, whose major idea was the injection of DC rather than AC current to avoid induction effects.