AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Structural Inheritance in the Barmer Basin, India: Its Influence on Early-Stage Rift Evolution and Structural Geometries

Abstract

Pre-existing structures have long been known to affect the evolution of rifts and influence their structural geometries. Consequently, structural inheritance can play an important role in defining all aspects of hydrocarbon systems within extensional sedimentary basins. In this work we describe the characteristics and effects of structural inheritance upon the development of the Barmer Basin, India, and we discuss the implications of this in the wider context of extensional basin evolution. Working across two scales of investigation we combine targeted field mapping with sub-surface seismic interpretation to construct a structural model that focuses on the early basin fill local to the field area and shows how early-stage rifting was accommodated. We find evidence for multiple episodes of rifting, with structural inheritance influencing both. The effect of pre-existing structures during each rift-episode varied. At the small-scale, an early extensional event was accommodated by localised reactivation of pre-existing, extension-oblique structures acting in combination with the evolving rift-structures. At the basin-scale, the structures generated during this early episode of rifting were variably utilised during a subsequent episode of rifting. Significantly, a large-offset (=3km), rift-oblique structure was incorporated into the evolving eastern margin fault system and facilitated displacement transfer between offset fault-systems to its north and south, generating a complex accommodation structure between two oblique (120°) structures. This type of accommodation zone is significantly different in geometry to classical accommodation zone models between two sub-parallel structures as it transfers displacement through extensive block-rotations and fault splays. Our results show the important affect that pre-existing crustal structures have on the structural geometries generated during early-stage rifting. The structural relationships described here do not fit with ‘classical’ extensional margin or accommodation zone models and, as a result, early depocentre location and linkage in the Barmer Basin deviated from accepted models of depocentre evolution. We find that structural inheritance may manifest itself as small-scale (sub-seismic) structural complexities that can compartmentalise a reservoir, detrimental to its quality, or at the basin-scale, control early sediment routing and depositional systems that are key for understanding all petroleum plays.