Deep reservoir forming mechanism in the upper part of the fourth member ofShahejie Formation in Bonan subsag of Shengli Oil Field

The features of fault block types of the crust,well developed deep-fault,Moho uplifting and lithosphere thinned and geothermal flux going up,and extensively developed igneous rocks of mantle source rocks in Bonan subsag show that the deep thermal fluid related to subalkali-alkali magma existed in this area in Paleogene period.In addition,there existed mantle inorganic CO₂ pool,and the findings of the high hydrothermal altered mineral-wollastonite and low values of hydrothermal altered mineral-NaAICO₃, ⁸⁷Sr/⁸⁶Sr, δ¹⁸O were found.The metal-rich ions and clay mineral were abnormally evolved.It is proved that the deep reservoir possesses all conditions of dissipation system, and the deep thermal fluid with initial strong acid is one of the most important factors forming secondary pores.The double-diffusive-circula-tive convection mechanism of pulsating deep thermal fluid is expounded in this paper.