Fluid Inclusions and Their Application in Hydrocarbon History and Genesis

The fluid inclusions characteristics and pore fluid salinity of 56 samples from clastic reservoir of the Lower Cretaceous were analyzed in the Tanzhuang Sag. The authors also discuss the hydrocarbon charge history and the genesis of secondary pores in the Lower Cretaceous. The multipeak distribution of homogenous temperature of the brine inclusions showed that the inclusions captured should be multiperiod fluids at various depths. Comparison of the homogeneous temperature of brine inclusions with the temperature on the burial history curve suggested that the source rocks had entered the stage of large-scale hydrocarbon generation. However, only individual brine inclusions containing methane were found, and no oil-bearing inclusions were seen. The absence of oil-bearing inclusions indicated that no large-scale oil charges and limited favorable mature source rocks were present in the study area. The paleosalinity varied with depth and was divided into three zones, namely two low-value zones in the shallow and deep burial and one high-value zone in the medium burial. The secondary pores were relatively developed in the high-salinity fluid zone. Secondary pores are chiefly related to the inorganic acid associated with dehydration and mutual transformation of clay materials, and to the organic acid released from limited mature organic matter.