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Allen, Mark1, Eric Blanc1, Christopher Wibberley2
(1) CASP, Cambridge, England
(2) Université Nice-Sophia Antipolis, 06560 Valbonne, France

ABSTRACT: Faults and Fractures in Anticlinal Reservoirs in the Middle East and South Caspian Regions

Exposed anticlines in the Middle East (Oman, Zagros) and South Caspian (Azerbaijan) help constrain the fault and fracture properties of carbonate and clastic reservoirs respectively. In all cases the characteristics of fault and fracture sets are correlated to the deformation history, particularly with respect to folding mechanisms and the likely stress evolution during folding. Fold orientation with respect to the regional convergence introduces a preferred orientation to oblique-slip faults, that may be under-represented in current models. Pre-fold and syn-fold faults are also important in controlling fracture development during folding in carbonate anticlines, whilst late or post-fold faulting commonly develops independent fracture clusters. Fracture porosity is not important in South Caspian clastic reservoirs, but microfracturing may have negative impacts on primary porosity. Faults aid rapid secondary migration into reservoir sands in overpressured conditions, but act as baffles or seals between reservoir compartments. Fracture porosity characteristics in carbonates depend on the mechanical properties of a given lithology. Diagenetically altered units such as hardgrounds or palaeokarstified units exert a control on the development of later fracture arrays. Fracture porosity can be destroyed by calcite cementation, but cemented fractures can reopen under certain stress conditions to act as conduits to fluid flow or as surface fissures held open during reburial by porous sediment infill. Such diagenetic controls highlight the sensitivity of final fracture array properties to the burial and uplift history in relation to folding and fracture generation.

 

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004