Abstract
— In situ stress and pore pressure data from the Valhall and Ekofisk oil reservoirs indicate that at the onset of production in both fields an incipient state of normal faulting existed in the crest of the anticlinal structures. In contrast, on the flanks of the structures the initial least principal stress values indicate an almost isotropic state of stress. Oil production from both fields caused marked pore pressure reductions as well as poroelastic reductions of the least principal stress in both the crest and flanks of the two structures. We demonstrate that as a result of production-induced pore pressure and stress changes, normal faulting appears to have spread out from the crests of the structures on to the flanks. Further evidence of a normal faulting stress state at Valhall has been found using data from a passive seismic monitoring experiment. Numerous microearthquakes were recorded during a six week monitoring period that are located at the very top of the reservoir or in the shale caprock immediately above it. An inverse/composite focal plane mechanism of these microearthquakes is consistent with a normal faulting stress regime.
Similar content being viewed by others
Author information
Authors and Affiliations
Additional information
(Received July 18, 2000, revised/accepted December 21, 2000)
Rights and permissions
About this article
Cite this article
Zoback, M., Zinke, J. Production-induced Normal Faulting in the Valhall and Ekofisk Oil Fields. Pure appl. geophys. 159, 403–420 (2002). https://doi.org/10.1007/PL00001258
Issue Date:
DOI: https://doi.org/10.1007/PL00001258