Posted on 23/07/2013
The Tectonic Studies Group has existed since the early 1970s as a forum for discussion of research instructural geology and tectonics. For 2013, the Tectonic Studies Group Annual Meeting was convened by structural geologists based at the University of Leeds.
Tetsuzo won the Best postgraduate poster prize for his poster on ‘Fracture networks and associated local stress fields in asymetric folds at Saundersfoot, the South Wales Coalfields’.
Fracture networks have great effects onpermeability and fluid transport in many hydrocarbon reservoirs. There havebeen many studies in the past decades on the development of fracture patternsin relation to regional-scale fold formation with a view of understandingbetter the permeability of oil and gas reservoirs. However, no clear andgenerally accepted relationships between them have been established as yet, butthe topic continues to be of major interest in the petroleum industry. Here wereport the results of a study of fracture networks in alternating sand-shalelayers at outcrop-scale in relation with map-scale asymmetric folds in Saundersfootin the South Wales Coalfields. A total number of 1,879 fractures have beenstudied. The fracture populations can be divided into two main relative-age groupsbased on the field observation. The older group constitutes fractures generatedduring extensional sub-parallel to the map-scale fold axis; the younger group constitutesfractures formed during extension sub-perpendicular to the fold axis. Thefractures in both groups are either extension or hybrid (extension and shear) fracturesMany extension fractures in the sandstone layers become arrested at thecontacts with the shale layers; those fractures that penetrate the shale layersare mostly hybrid and tend to have smaller apertures than the pure extensionfractures in the sandstone layers. The results have clear implications for thevertical permeability of reservoirs composed of similar layers and indicatethat the horizontal permeability is, for such reservoirs, much greater than thevertical permeability.