The Effect of the 1993 Stimulations of Well Gpk1 at Soultz on the Surrounding Rock Mass: Evidence for the Existence of a Connected Network of Permeable Fr

Abstract

Spinner logs run during tests which followed the massive stimulation of a well in granite show only 12 fractures which account for 95% of the flow. Yet the scale and intensity of microseismicity during the stimulation suggests that many fractures intersecting the wellbore should be permeable. In this paper we augment the spinner logs with temperature logs to better define the population of flowing fractures and hence clarify the nature of the rock mass about the well following stimulation. The results indicate that 20% of some 500 fractures seen on BHTV images support flow. Based on this and other indications of connectivity, we propose a conceptual model of the rock mass in which the well is surrounded by a network of connected highly-permeable fractures. However, the stimulation of this network does not extend sufficiently far from the well to intersect the major fault-like structures within the granite that serve as sources and sinks of flow during hydraulic tests.