Western Liaoning - North Hebei Province And Neoproterozoic Oil And Gas Migration And Accumulation Of The Study

As one of the new means for petroleum geochemical research, fluid inclusion technique has been widely used not only in research of time, temperature and period of hydrocarbon migration and reservoir charge, and property and source of fluids, but also in gas-oil prospective appraisement. This paper applies this technique for the first time in China to the research on the charge times and stages of hydrocarbon migration and accumulation in Mid-late Proterozoic in West Liaoning-North Hebei. The microscopic temperature measurement as well as composition, assemblage and formation period analysis of hydrocarbon inclusions, combined with the study on the occurrence and distribution of asphalt and oil seepage in reservoirs, provide an new insight into the reservoir charge history. The asphalt and oil seepage widely appear in outcrops of the Mid-late Proterozoic sedimentary strata of marine carbonate rocks in West Liaoning-North Hebei of North China. The data systematical analysis and field geological investigation support occurrence of favorable geological conditions for the formation of primary reservoirs in the Mid-late Proterozoic strata in the study area. These conditions include large volume sedimentary rocks in the strata, some sequences of which are rich in organic matter with higher evolution, carbonate rock reservoirs that have a great number of apertures and cavities formed by several episodes of tectonic movement and being favorable to hydrocarbon migration and accumulation, and favorable stratigraphic assemblages for hydrocarbon generation-reservation-seal formed in a multi-cycle sedimentary process. The asphaltum and oil seepage occur in outcrops generally as liquid crude oil, sometimes as dense oil, and rarely as solid asphaltum. They are dispersed or distributed in cracks, corrosion pores, intergranular holes, and sutures. It is shown that the Tieling and Wumishang Formations are the top two oil-generating horizons in the Mid-late Proterozoic strata in the research area. The research on the charge times and stages, GOIs and assemblages of petroleum inclusions, as well as microscopic and macroscopic characteristics of the asphaltum and oil seepage provides some evidence for existence of 3 to 4 stages of hydrocarbon migration and reservation in Mid-late Proterozoic in West Liaoning-North Hebei. The stage and scale of gas-oil activities are different in different areas or horizons. The hydrocarbon formed early is primary heavy oil with low maturity. In contrast, the hydrocarbon formed late is light oil with high maturity, activity of which on a large scale shown by movement of hydrocarbon through crannies and pores is related to tectonic movement. The inclusion homogenization temperature measurement and salinity determination lead to division of the formation process of the reservoir into 3 stages, which is consistent with the result the microscopy observations. The component analysis of hydrocarbon inclusions by use of Micro-FTIR indicates that there are at least 2 stages of hydrocarbon charge in the research area. Through examination of absorbance peaks of –CH₂ and –CH₃ and their ratios, combined with corresponding microscopic observation of hydrocarbon inclusions, it has been found that the inclusions with higher ratios of CH₂ to CH₃ are not fluorescent or weakly fluorescent, and represent the products of heavy oil formed by evolution of hydrocarbon source rocks from low maturity to medium maturity. In contrast, the inclusions with lower ratios of CH2 to CH3 have yellow or blue fluorescence, and are the products of medium to light oil formed by evolution of hydrocarbon source rocks during the oil-generating peak period. These products may be main part of hydrocarbon reservoirs in Mid-late Proterozoic in West Liaoning-North Hebei.