The modern geothermal field and hydrocarbon generation/expulsion in Lufengbei Area, Pearl River Mouth Basin

To understand the thermal evolution and hydrocarbon generation potential of source rocks of the Lufengbei (in which bei means north in Chinese) half-graben (LFB), available abundant data from the Lufengnan (in which nan means south in Chinese) half-graben (LFN) and the measured data of formation temperatures and vitrinite reflectance from drillings through source rocks were used to analyze the correlation between formation temperatures and burial depth by forward simulation. In addition, by extrapolation from the more-drilling area of LFN to the less-drilling area of LFB, the regional geothermal field of LFB was systematically established for the first time. Based on the geothermal field model, the basin simulation genetic method was applied to evaluate the impact of the geothermal field on the thermal evolution of source rocks, and further assessed quantitatively the hydrocarbon generation potential. Results show that first, the LFB has smaller geothermal gradient and lower temperature in the central areas of depression, and vice versa in the marginal highland of depression. The main source rocks of the Eocene Wenchang Formation in LFB have been mature in overall at present, especially in the central aeras of depression entering highly matured stage. Secondly, the biomarker fingerprints of drilled mudstones indicate for the first time that the upper Wenchang Formation contains source rocks of shallow lake and semi-deep lake facies, confirming that LFB has a good hydrocarbon potential. Thirdly, LFB experienced two episodic oil expulsion stages (35.5-26.5 and 17.5-8.5 Ma) and the gas expulsion stage is 15-0 Ma. Therefore, the order of hydrocarbon resource enrichment degree is: Subsag LF07 ＞ Subsag HZ11, ＞ Subsag HZ05, and the structural zones surrounding Subsag LF07 was identified as favorable exploration zones.