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Structural Restoration of the Jurassic Section at Kra Al-Maru and Riksah Structures, West Kuwait

Abstract

Jurassic reservoirs in Kra Al-Maru and Riksah areas, consists of two reservoir units from base up as a heterogeneously interbedded limestone, dolomite and anhydrite succeeded by an upper homogeneous succession composed mainly of tight limestones, carbonaceous shales and kerogen. Both the units are capped by a thick cyclic salt and anhydrite sequences. The rock succession has a simple stratigraphic configuration; however the tectonic events that this area has undergone are complex. In an attempt to capture major tectonic variables associated within the study area during the Jurassic, structural restoration by backstripping and Finite Element Method has been used. The reason behind doing such analysis is to understand the kinematics and the drivers behind negative inversion along the major dextral strike-slip fault system. Two representative cross-sections have been utilized for the restoration. One cross-section along WNW-ESE and the other along NE-SW has been used. The cross-sections are perpendicular and parallel to the major strike-slip faults, so that the variations in fault kinematics are adequately captured. The structural restoration analysis reveals that during the Lower-Jurassic the study area is subjected to extension, followed by two stages of compression and a stage of strike-slip movement in the Upper-Jurassic. During Neocomian, earlier deposited salts are compacted, consequently leading to lateral salt movement and thrusting. It is therefore inferred that local tectonics has its own fingerprint in the area which is superimposed by regional plate-wide tectonic stresses. The analysis is proven to be vital for prospect evaluation. The study shows that Riksah structure has been subjected to series of uplift and subsidence events leading maximum strain and stress concentration in the area. Such concentrations would result in congenial natural fracture system and help upgrading the prospectivity of Jurassic units in the area and adjoining exploratory areas as well.