Analyse On Hydrocarbon Accumulation System In Huizhou Depression

Huizhou depression in Pearl River Mouth Basin is very important offshore petroleum area, and LH11-1 Oilfield located on eastern part of Huiliu structure ridge has a giant petroleum reserve （24000x10⁴t）, which is the largest oilfield in Pearl River Mouth Basin up to now. Many researchers have done lots of work in this study area, however, the issues that hydrocarbon accumulation contribution of two suits of main source rocks and characteristics of hydrocarbon migration and accumulation still exist because petroleum features of Huizhou Depression are very complicated. In this study, hydrocarbon accumulation mechanism, hydrocarbon accumulation model, and petroleum distribution rule of petroleum system are analyzed by using petroleum geology, geophysical and geochemical data.Based on source rocks characteristics of different sedimentary facies in Huizhou Depression, we proposed a suit of evaluation standards for excellent source rocks of different sedimentary facies in Huizhou Depression. The TOC of deep lacustrine facies mudstone in Wenchang Formation reaches 3.0% while the TOC of its shore-shallow lacustrine facies mudstone is larger than 6.3% suggesting it is excellent source rock. Excellent source rocks of Wenchang Formation SQ2 mainly distribute in LF13 Sag, HZ26 Sag, and XJ24 Sag. Source rocks in Enping Formation are subordinate source rocks in this study area, and good source rocks mainly developed in HZ08 Sag, HZ13 Sag, and LF13 Sag.According to analyses of resin compounds content, C₃₀-4-methyl sterane, distribution pattern of C27-C28-C29aaaR Sterane, andαβC₂₉Hopane /αβC₃₀Hopane, the source rocks of Wenchang Formation can be divided into three types:Type 1 is middle-deep lacustrine facies source rocks without terrigenous input; Type 2 is middle-deep lacustrine facies source rocks with terrigenous input; Type 3 is shore-shallow lacustrine facies source rocks.Based on hierarchical cluster analysis and geochemical characteristics of oils, Ois in Huizhou Depression also can be divided into three types. They are oils （mainly distribute in Huidong half-graben, Liuhua Oilfield, and panyu4 Sag） derived from middle-deep lacustrine facies source rocks without terrigenous input, mixed oils （mainly distribute in HZ26 Sag and wells around XJ24 Sag） derived from source rocks with terrestrial high plants and lacustrine bog inputs, and oils （e.g. HZ9-2-1） mainly derived from Enping Formation respectively.Hydrocarbon generation kinetics of source rocks are used to reappear the hydrocarbon-generating process of source rocks in different geological conditions, confirm the characteristics of hydrocarbon generation kinetics for organic matters with different microscopic components, and identify the hydrocarbon-generating content history of different types of kerogen.Two types of hydrocarbon accumulation pattern are concluded. One is long distance lateral and stepladder migration, and the other one is fault migration.