Characteristics of a geothermal anomaly in the Fushan Sag, Beibuwan Basin, China, and its effects on oil and gas reservoirs

Abstract

This study examines a particular phenomenon associated with a geothermal anomaly which is inconsistent with the basement structure of the Fushan Sag in Beibuwan Basin, China. The characteristics and forming mechanism of the geothermal anomaly are discussed based on geothermal data analyses and a paleo-geothermal simulation. The results indicated that the current value of geothermal flow in Fushan Sag is 86.4 mW m−2 on average. In contrast, the paleo-geothermal flow value is 77.7 mW m−2 on average. The current geothermal field of the Fushan Sag has higher temperatures than the paleo-geothermal field, and geothermal anomaly occurs in the current geothermal field. The basement structure, the typical anticline structure, the accumulation of hydrocarbons, and the deep magma chamber are the reasons for the geothermal anomaly. The geothermal anomaly has been linked to deep magma body, which is located in depth of 15 km near the Bailian district. The formation of the geothermal anomaly occurred 10,000 years ago and was relatively short, having little effect on the maturity of organic matter. However, a large number of paleo-oil reservoirs were thermally pyrolyzed into condensate gas reservoirs at the center of the abnormal geothermal area, which had a significant effect on paleo-oil reservoir in the Fushan Sag.