Cross-Strike Structures and Hydrocarbon Migration and Accumulation: Examples on the Relationship Between Strike Slip Faults and Lateral Ramps in Three Alpine Thrust Belts

Abstract

Cross-strike structures or transverse zones are discontinuities trending remarkably oblique to the thrust belt structures causing sharp along-strike variations and lateral changes (Leslie et al. 2010). Among the possible causes controlling the location of cross-strike structures and transverse zones are (1) preexisting sub-décollement basement faults, (2) cover strata deformed above basement faults, and (3) along-strike variations in mechanical stratigraphy and lateral thickness/facies changes. Commonly, these cross-strike structures are constituted by regionally important faults or array of faults mostly represented by lateral/oblique thrust ramps, oblique faults, strike-slip or transfer faults. The study focused on the comparison between three case studies related to three different carbonate-dominated Alpine-type fold-and-thrust belts: the Zagros in the Kurdistan region of NE Iraq, the outer Albanides in Albania and the Central Apennines in southern Italy. Selected thrust-related structures are investigated by means of remote sensing (LANDSAT ETM+ and QUICKBIRD satellite images) analysis allowing large-scale structural reconstructions integrated also with some field observations. The considered thrust belts have in common a similar genesis as they formed at the expenses of formely passive margins, which were developed over the Mesozoic Neo-Tethys Ocean. In that sense, they present similar structural characteristics allowing straightforward comparisons among structures. The cross-like transverse structures have a critical impact on controlling different modes of fluid pathways. Furthermore, they can affect the development and distribution of fracture patterns within thrust-related anticlines. By comparing selected practical cases coming from similar thrust belts, the results of this study suggest that cross-strike structures have a dramatic impact on hydrocarbon migration and accumulation. They mostly act as structural barriers to lateral fluid migration being crucial in compartmentalizing the reservoirs and contributing in localizing hydrocarbon accumulation. Generally, the fracture intensity is variable and it increases up drastically approaching closer fault zones. Considering the lithological units, structures and stresses, the characterization of fractures network along cross-strike faults is fundamental and contribute to understand fluid migration behaviours within carbonate reservoirs having potentially a positive impact for hydrocarbon exploration.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016