Magmatic activity and hydrocarbon potential revealed by Paleozoic collapse structures in the Hangjinqi area, northern Ordos Basin, China

Abstract

Collapsed reflections of lower Ordovician carbonates and upper Carboniferous-lower Permian coal-bearing strata occur below the middle Permian lower Shihezi Formation in the Hangjinqi area, northern Ordos Basin. This study takes advantage of three-dimensional seismic data, logging data, core data and well-testing data to investigate the genesis of the collapsed reflections and their implications for hydrocarbon potential. These collapse structures have a subcircular appearance in map view. The columnar reflections in the basement and the volcanic tuff in the lower Shihezi Formation around collapse structures indicate that the formation of these structures are related to magmatic activity. Most of the collapse structures terminate upward in the H1 member of the lower Shihezi Formation, which explains its greater thickness and supports the hypothesis that magmatic activity occurred during the depositional stage of the lower Shihezi Formation in the early middle Permian. The collapse structures can increase the thickness and space of the reservoirs, and the collapse of magma conduit can also increase the thickness of the regional sedimentary cap rock above the collapse structures and improve the sealing capacity of the cap rock. These results provide insights into the magmatic activity and hydrocarbon potential of Paleozoic rocks in the Ordos Basin.