Chapter from:
AAPG Memoir 67: Seals, Traps, and the Petroleum System, Edited by R. C. Surdam
(Publication Subject: Oil Methodology, Concepts)
AAPG Memoir 67: Seals, Traps, and the Petroleum System. Chapter 7: Microstructures and Diagenesis in North Sea Fault Zones: Implications for Fault-Seal Potential and Fault-Migration Rates, by S.J. Hippler, p. 103-113

Chapter 7

Microstructures and Diagenesis in North Sea Fault Zones: Implications for Fault-Seal Potential and Fault-Migration Rates

by

S.J. Hippler¹
Exxon Production Research Company Houston, Texas, U.S.A.
¹Now with Exxon Exploration Company, Houston, Texas

The deformation mechanisms and diagenetic events that determine the fluid-flow properties of North Sea faults have been established by characterization of faults in core and thin section. The results of this study have implications for predicting fault-seal potential and fault-migration rates.

In the northern North Sea, faulting of weakly lithified sand and shale units was accomplished via independent particulate flow, in which grains are disaggregated and reoriented without grain fracture. In the southern North Sea, faulting of lithified sandstone units was dominated by grain fracture and grain size reduction. Capillary pressure measurements of the deformed samples indicate that both independent particulate flow and cataclastic deformation mechanisms result in relatively low permeability fault zones in comparison to the surrounding reservoir rocks. Cements are commonly observed within the North Sea fault zones and also contribute to the permeability reduction. Simple calculations using the fluid-flow measurements suggest, however, that faults with good sealing potential can allow hydrocarbon migration over geologic time scales.