Abstract

The Euphrates Graben in East Syria is a "hidden" intra-cratonic rift-basin of some 120 km wide, formed by crustal extension in the Middle to Late Cretaceous. Pre-rift clastic reservoirs, differentially subsided along a complex pattern of faults, are charged from syn-rift source rocks and covered by a thick late syn-rift to post-rift seal. An early syn-rift waste rock unit exerts a decisive control on trap size in large part of the basin. Static and dynamic field models, as well as positioning of wells have proven to be critically dependent on definition of faults, and characteristics of fault geometries. Structural geological data from a variety of seismic attribute images were compiled and synthesised into a consistent and geomechanically viable regional structural framework of the basin and its fields, in order to contribute to better definition of its hydrocarbon volumes, to enhance hydrocarbon recovery, and to improve subsurface targeting of wells. The fault pattern of the rift basin is organised according to a number of highly interlocking but laterally persistent trends, most of which are inherited from already existing anisotropies in structural basement and its pre-rift overburden. A diffusely distributed and limited component of northerly trending left-lateral shear appears to be a major contributor to structural complexities within the basin. Relatively simple interpretation concepts of composite faulting, consistent with the regional framework and underpinned by experimental models and outcrop analogues, have contributed to a better understanding of the basin and its fields.

Introduction

The Euphrates Graben is a "hidden" intra-cratonic basin of some 120 km wide, which was formed by a SSW – NNE oriented crustal extension event during Middle to Late Cretaceous time (Lovelock, 1984; de Ruiter et al., 1995; Litak et al., 1998). The rifting and its associated structural relief followed a Base Upper Cretaceous Unconformity (BKU, Figures 1 and 2) of regional extent. Pre-rift clastic RESERVOIRS of the Mulussa F and Rutbah Formations (Figure 2), differentially truncated at this BKU and a more local rift-basin unconformity (RBU), subside along a complex pattern of highly interlocking faults according to different trends.

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