Mantle-Derived Fluids and Their Effects on Oil/Gas Generation in Sedimentary Basins

Zhijun Jin¹, Liuping Zhang², and Wenxuan Hu^3
1 Research Institute of Petroleum Exploration and Development, Beijing, China
² Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
³ Nanjing University, China

Significant quantities of mantle-derived fluids have been discovered in the Songliao and Bohai Bay basins, the most petroliferous provinces in China. Although such fluids are common in many of the sedimentary basins around the world, little is known about their characteristics and their effects on oil and gas generation in the basin. The paper reports the isotope and molecular geochemistry and thermodynamics of mantle-derived fluids in the Dongying Depression, Bohai Bay Basin. Two types of mantle-derived fluids have been identified, with one being enriched in CO2 (H2O+CO2+CH4) and another H2 (H2O+CH4+H2). Quantitative studies of thermal energy transfer show that the mantle-derived fluids are an effective heat carrier, and the thermal anomalies identified demonstrate clear thermal effects of mantle-derived fluids. As hydrocarbon generation from kerogen degradation needs not only thermal energy but also hydrogen, the results of laboratory simulations illustrate significant enhancement of hydrocarbon generation by kerogen hydrogenation. This enhancement, up to 147%, is evident for the post-oil window hydrocarbon generation from type I and II kerogens, whereas the hydrocarbon generation rate is increased at every maturation stage for type III humic kerogens. As mantle-derived fluids appear to affect significantly hydrocarbon generation by providing both energy and hydrogen, source rock hydrogenation may lead to substantial amounts of petroleum resources in sedimentary basins that are currently overlooked.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005