Mud-Diapirism Induced Structuration and Implications for the Definition and Mapping of Hydrocarbon Traps in Makran Accretionary Prism, Pakistan

Abstract

The mobile mud coupled with tectonic forces has played an important role in shaping the structural styles as well as geomorphic features in Makran Accretionary Prism. At surface, key structural elements associated with mud tectonics such as broad synclines, very tight anticlines and mud volcanoes have been observed particularly in southeastern part of Makran Accretionary Prism. There are often associated emanating methane gas with mud volcanoes. In subsurface, mud walls and Mud diapirs have been envisaged in the cores of anticlines separated by less deformed broad synclines representing possible mud withdrawal areas. Occasionally, anticlines encircle the synclines and form dish like geomorphic feature, which appear like mini basins same as the one associated with salt tectonics. These kinds of mini basins usually act as depocentres for the sediments eroded from adjacent growing anticlines as well as for pounded turbidites from regional sediment supply. It is also envisaged that the strata probably truncate against the Mud walls as in analogous geological settings. Folding related fracture sets and strike slip faults have facilitated the extrusion of the mud at surface. This phenomenon is characterized by occurrence of active as well as passive mud volcanoes in the study area. Results of the study suggest that potential hydrocarbon traps in the region of Makran Accretionary Prism could be associated with the truncation of strata against “Mud walls” and around “Mud diapirs” with hydrocarbon accumulations at the limbs of anticlines. To date, a number of dry wells have been drilled in Makran Accretionary Prism, mostly targeting the crests of these mud-cored anticlines, which could be one of the reasons of not finding the predicted reservoirs, let alone the hydrocarbons. Due to the same geological reason, drilling hazards while drilling through the over pressured mudstones have also led to mechanical failures in some of the wells i.e Dhak anticline wells. The proposed paradigm shift in defining the hydrocarbon traps and locating the exploratory wells on these structures has significant implications for petroleum exploration in the region.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015