Print this pageStructure, Formation and Petroleum Implications of Piercement Structures in Sedimentary Basins
Piercement structures are cylindrical, pipe-like features intersecting the layered sequences in sedimentary basins. They include mud volcanoes, hydrothermal vent complexes, breccia pipes, dewatering pipes, and pockmark complexes. The structures are formed by pressure buildup and fracturing of the overbuden. Active pockmarks are found along the Mid-Norwegian Margin, e.g., in the Nyegga area and on the margin west of Svalbard. The pockmarks were formed by episodic expulsion of hydrocarbon gases through the gas hydrate stability zone. Thousands of pockmarks have further been identified on multi-beam bathymetry data in the North Sea. Detailed sampling and analyzes of these pockmarks show that they are extinct. They were likely formed about 11,000 years ago during the last deglaciation. Active mud volcanoes are commonly found in compressional basins with rapid sedimentation, e.g., in the Caspian Basin in Azerbaijan and on Java, Indonesia. The mud volcanoes are sourced by maturation of deep organic-rich sedimentary sequences. Fossil piercement structures are common in the Vøring and Møre basins offshore Mid-Norway. We have mapped about 800 kilometer-sized hydrothermal vent complexes in these basins. The vent complexes were formed by expulsion of metamorphic fluids and gases during emplacement of magmatic sheet intrusions at the end of the Paleocene, about 55 million years ago. Similar vent complexes are common in other volcanic basins, e.g., the Karoo Basin in South Africa and the Tunguska Basin in Siberia. Dewatering pipes, mounds, and mud volcanoes are further common in the Tertiary successions in the Vøring Basin. The piercement structures may have implications for petroleum exploration, as 1) active piercement structures represent geohazards for platforms and drilling operations (e.g., Azerbaijan, Indonesia), 2) fossil piercement structures may form high-permeability conduits leading to focused fluid flow of hydrocarbons both in to, and out of, reservoirs, and 3) for exploration, the presence of piercement structures may suggest the presence of a hydrocarbon system.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil