| With the development of petroleum exploration theories and advances in technology, ultra-deep sequences in sedimentary basins have become one of the important fields of petroleum exploration. According to the results of the evaluation of oil and gas preservation conditions in ultra-deep oil and gas exploration, it could be concluded that the parameter indexes for the evaluation of ultra-deep oil and gas preservation are different from those in middle and shallow sequences. The preservation of the ultra-deep oil and gas probably is mainly controlled by the factors such as formation temperature, pressure, hydrocarbon generation/filling time, reservoir rock mineralogy characteristics and tectonic events. In the ultra-deep sequences, the hydrocarbon phase state transformation is generally controlled by temperature, the cap rock overpressure fracture is controlled by pressure, the diffusion loss is controlled by the accumulation time, hydrocarbon components and cap rock physical properties, hydrocarbon destruction owing to chemical reactions is controlled by reservoir rock mineralogy characteristics and hydrocarbon-fluid-rock interaction. The tectonic event controls the evolution of deep faults and therefore the vertical migration and loss of hydrocarbon. In short, the evaluation of ultra-deep oil and gas preservation should be carried out from two aspects: physical loss and chemical destruction. |
