From the burial history map of Deshan 1 well (Figure 9-20), it can be seen that the maturity of the Lower Carboniferous just entered the threshold of hydrocarbon generation at the end of the Early Carboniferous, and reached the early maturity stage at the end of Permian, with the Ro reaching 0.7% ~ 1.0%, and a small amount of liquid hydrocarbons began to be generated, while the upper Carboniferous was only 6544 due to shallow burial. Due to the influence of Indosinian movement, the Qaidam block was uplifted and denuded in the Late Triassic, resulting in no Triassic deposits in the basin today, and the Permian system was missing as a whole. In some areas, the Zabusagaxiu Formation and Kruke Formation of the Upper Carboniferous were also denuded, and the maturity of the Lower Carboniferous stopped and the hydrocarbon generation process was interrupted. At this stage, the maturity of Carboniferous source rocks has never reached the late maturity stage, that is, Ro has not reached 1.0% ~ 1.3%, and there is no large amount of hydrocarbon generation.
Figure 9-20 Buried History Curve of Deshan 1 Well in the East of Qaidam Basin
In the early Jurassic, under the weak extension from north to south, the Delingha area formed a fault depression, which was deposited in the lower and middle Jurassic, but the Carboniferous did not reach the historical maximum burial depth, and the thermal evolution of organic matter was in a stagnant state. At the end of the middle Jurassic, due to the early Yanshanian movement, the structure of the early and middle Jurassic fault basins was reversed, the fault basins were uplifted, the middle and lower Jurassic were generally denuded, and the Carboniferous was buried shallowly, which did not reach the oil generation window temperature. From late Jurassic to early Cretaceous, it settled again, and the upper Jurassic and lower Cretaceous were deposited continuously. From late Cretaceous to Carboniferous, it reached the window of oil generation and produced a small amount of hydrocarbons. The late Yanshanian movement at the end of Cretaceous caused the area to rise again, and the hydrocarbon generation process of Carboniferous was interrupted again. Cenozoic continuous deposition of Paleogene-Neogene and Quaternary, Himalayan movement has certain influence on this area, but it is not obvious in Deshan 1 well. The buried depth of Neogene Carboniferous system is the largest, close to 5000m, and the maturity reaches the mature-high mature stage, and the source rocks begin to generate a large number of hydrocarbons.
According to the burial history of Deshan 1 well, there are multiple hydrocarbon generation and expulsion periods in Carboniferous in Delingha area, among which the late Carboniferous-the end of Early Triassic and the end of Paleogene-the present are the most important two hydrocarbon generation and expulsion periods.
According to the graphic display of the burial history of Gaqiu 1 well in the south of Luliang Mountain (Figure 9-2 1), the evolution history of Carboniferous source rocks in the south of Luliang Mountain is basically similar to that in Chaidong area, and it has also experienced four subsidence and three uplift. Carboniferous source rocks reached the peak of hydrocarbon generation from the end of early Permian to late Permian, and a small amount of source rocks began to generate gas at the end of late Permian. After that, the subsidence and uplift are basically the same as those in Chaidong area.
Fig. 9- Maturity history of Carboniferous source rocks in Gaqiu 1 Well.