Tectonic Thermal Evolution History Of The Kwanza Basin

This paper primary researched hydrocarbon source rocks in pre-salt layer which is located in deep water area of Kwanza basin by one-dimensional basin simulation technology. Combined with seismic data and geological data, the tectonic evolution history and and thermal evolution history of Kwanza basin was recovered, and the distribution of hydrocarbon source rock’s maturity degree was analysed.The tectonic evolution history was recovered by the method of equilibrium profile, the sedimentary burial history was recovered by the forward and inversion method. This paper combined the method of tectonic thermal evolution and geothermometer method, to restore Kwanza basin’s thermal evolution history and calculated the pre-salt hydrocarbon source rock’s maturity. The main conclusions are as follows:Combined Kwanza basin tectonic evolution and Sedimentary burial history, the characteristics of tectonic evolution was analyzed:the sedimentation rate of rift depression period (140Ma-131Ma) and sag depression period (131Ma-123Ma) is high, the sedimentation provenance was sufficient in this period and it was a rapid sedimentation process; In Aptian initial thickness of salt rock sedimentation (123Ma-110Ma) was about 600m. Owing to the effect of tectonic movement, the extrusion and extension zone was formed in later evolution process; the sedimentation rate of drift period (110Ma-0Ma) was low and it was between 20-40m/my; the sedimentation rate in late drift period was increased to 80m/my and the reason was that large amounts of terrigenous clastic sedimentary was generated by the uplift of the eastern part of Kwanza basin.The thermal evolution simulation results of Kwanza basin show that the pre-salt strata was in high-over mature stage in north of western depression zone of the main Kwanza basin and it tended to generate gas; the pre-salt strata was in mid-high mature stage in south of western depression zone of the main Kwanza basin and it tended to generate oil. The pre-salt strata was in mid-high mature stage in north of eastern depression zone of the main Kwanza basin and it tended to generate oil; the pre-salt strata was in low-high mature stage in south of eastern depression zone of the main Kwanza basin and it tended to generate oil. The maturity of Benguela basin’s thermal evolution is very high, so it contributed little to the formation of oil and gas reservoirs.