Model Research Of Generation Of Hydrocarbon Coal Source Rock In Xihu Depression

Xihu Depression which is one of the largest sedimentary depressions in China offshore Paleocene petroliferous basin (just smaller than Yinggehai Basin) is a very important petroleum exploration area in China sea area. Giant excellent coal source rocks in Paleocene Pinghu & Huagang Formations are the main material base for hydrocarbon accumulation of Xihu Depression. Is the existence of excellent coal source rocks in Xihu Depression equal to giant hydrocarbon resources potential? This issue attracts comprehensive attention and controversy of petroleum geologist at home and abroad. Therefore the enhancement of research for Xihu Depression source rocks has significant theory and practical meanings, especially the research of hydrocarbon-generating characteristics.This paper based on the national key special project reevaluation for resources potential of offshore hydrocarbon-rich depressions and exploration direction of new areas & fields. New technologies and methods are used to analyze the main geochemical characteristics of organic matters in Xihu Depression; hydrocarbon-generating simulation of two types of organic matters in Xihu Depression are utilized to analyze the hydrocarbon-generating contributions from different organic matters and the final products (oil & gas); Based on hydrocarbon-generating simulation, burial history of source rocks, and process of hydrocarbon-generating evolution, the evolution models of coal & mudstone source rocks in Xihu Depression are built. The major results of this study are stated as follows:1)The development layers and lateral distribution of main source rocks in Xihu Depression have relatively strong heterogeneity, which results in unequal hydrocarbon distribution in different structural blocks.2)Coal source rocks of Xihu Depression mainly developed in transitional zone facie of sea and land, and terrestrial high plants sedimentary & filling is the main controlling factor of coal source rock heterogeneity in study area. 3)Geochemical analyses of source rocks in Xihu Depression indicate that oils in Hugang Formation are derived from mature Pinghu Formation coal source rocks and partial mature lower Hugang Formation mudstone source rocks, and oils in Pinghu Formation are derived from Pinghu Formation coal source rocks.4)Pinghu Formation coal source rock is main source rock in Xihu Depression. Lower Pinghu Formation mudstone source rock is subordinated source rock, the characteristic differences of sterane, terpane and compound-specific stable carbon isotopes support the possibility of hydrocarbon contribution from lower Pinghu Formation mudstone source rock.5)There are two types of distribution characteristics of hydrocarbon generation material in coal source rocks, and they are vitrinite dominative model and saporpelinite+exinite dominate model respectively. The simulation experiments indicate the oils generated from two types of coal source rocks are different. Oils in Huagang Formation are type II and oils in Pinghu Formation are type I. The differences of organic microscopic component results in distribution pattern of oils in upper layers and gas in lower layers in Xihu Depression.6)According to hydrocarbon-generating simulation experiment of source rocks, hydrocarbon-generating evolution characteristics of coal source rocks in study area are detailedly depicted, and appropriate hydrocarbon-generating evolution models matching study area are established.