Observation and simulation of non‐Darcian flow transients in fractured rock

TLDR

The study sets up a numerical model to evaluate two multirate flow experiments conducted in 1994 at the Soultz hot dry rock test site. The authors performed the experiments and developed a model that predicts turbulent fluid transport along a conduit with substantial surface area. The transient pressure records reveal clear non‑Darcian flow, and the best‑fit simulation—using a simple geometry—matches the data with physically reasonable parameters, confirming non‑Darcian flow along highly conductive features and the presence of high‑capacity far‑field faults.

Abstract

Two independent multirate flow experiments were conducted in 1994 in the open hole depth interval of a well bore at the hot dry rock (HDR) test site Soultz. The steady state and transient downhole pressure records gave clear indications of non‐Darcian flow. A numerical model has been set up to evaluate these two measurements. An excellent fit of the transient pressure responses of the two flow tests could be achieved by assuming one model of simple geometry. The model predicts fluid transport along a conduit with substantial surface area in which fully turbulent flow is occurring. All the parameters required by our best‐fit simulation fall into a physically reasonable range. Sensitivity analysis demonstrates a non‐Darcian flow regime along highly conductive features. The existence of high capacity far‐field faults as postulated in our model confirms earlier characterizations of the Soultz test site.