An analysis of geological characteristics and destruction types of hydrocarbon accumulation in the basin-mountain transitional zone on the western side of the Xuefeng Mountain

According to the researches on paleo-reservoirs in the basin-mountain transitional zone on the western side of the Xuefeng Mountain, this paper has summed up the basic characteristics of hydrocarbon accumulation, and recognized five petroleum-bearing combinations that might exist residually under the action of Yanshanian-Himalayan strong tectonic transformation. The typical reservoir-forming characteristics in this region is summarized. It is indicated in this paper that the hydrocarbon in lower Paleozoic sediments has the features of multiple-source hydrocarbon supplying and multi-stage hydrocarbon accumulation, the hydrocarbon experienced the stage of paleo-reservoir, and the tectonic uplift and erosion constituted the important factors for the unfavorable preservation conditions of hydrocarbon. Additionally, the preservation conditions of hydrocarbon are different in different regional cover residual zones and different tectonic parts. It is pointed out that there also exist some areas where the preservation conditions of hydrocarbon is relatively good in the strong late tectonic transformation region. These areas are mainly located in the fault footwall of the trough-like fold anticline, buried structures on flanks and synclinoria where the regional mudstone cap rocks composed of lower Cambrian and lower Silurian strata are distributed. Through the analysis of hydrocarbon accumulation and failure types, it is concluded that there are primary, secondary and regenerated reservoirs in the formation of the study area. Whatever the reservoir is, the probability that tectonic reservoir was preserved after the strong transformation of the tectonic reservoir is very small in the study area; nevertheless, the probability for the preservation of non-tectonic reservoirs (mainly the lithologic reservoirs) is relatively large. The classification scheme for five large classes and ten subclasses of reservoir failure types is proposed in this paper on the basis of an analysis of the failure conditions of the paleo-reservoir in the study area, and it is also indicated that there are many failure types of paleo-reservoirs.