Significance of fibrous mineral veins in hydrocarbon migration: fluid inclusion studies

Hydrocarbon migration pathways through impermeable mudrocks commonly involve fracture systems that include fibrous mineral growths, particularly fibrous carbonates and sulphates. The fibrous growths are believed to reflect precipitation in overpressured systems where fracture-walls are held apart by fluid pressure. Paragenetic studies for such fracture systems often show that hydrocarbon fluids predated the migration of aqueous fluids. Hydrocarbon migration is evinced by traces of solid bitumen along fracture walls or in between individual mineral fibres, and by hydrocarbon fluid inclusions within the mineral infills. Mineral in-fills with both hydrocarbon and aqueous inclusions offer the chance to determine palaeo-pressures and confirm if fibrous growths do represent over-pressuring. (C) 2000 Elsevier Science B.V. All rights reserved.