ANALYSIS ON THE CAUSES OF DIFFERENT ENRICHMENT OF HYDROCARBON IN GUDAO AND CHENGDAO BURIED-HILLS, JIYANG DEPRESSION

There are obvious differences between Gudao and Chengdao buried-hills in the degree of hydrocarbon enrichment, and the reason leading to such differences is still unclear. Base on relative researches and the organic geochemical characteristics and reservoir properties, the conditions of hydrocarbon accumulation occurred in Gudao and Chengdao buried-hills were compared, and controlling factors leading to the differences were analyzed. Both Gudao and Chengdao buried-hills are surrounded by hydrocarbon generation sags. Hence they both have favorable hydrocarbon source conditions. The dissolved pores and fractures in Gudao buried-hill are sparse, which causes low hydrocarbon charging efficiency in this buried-hill. It is such characteristics that lead to low hydrocarbon enrichment degree in Gudao buried-hill. In contrast, the dissolved pores and fractures in Chengdao buried-hill are enriched and the hydrocarbon charging efficiency is relatively high, which are also beneficial to form big pools in Chengdao buried-hill. Furthermere, the Dongying formation in Gudao buried-hill was eroded. Compared with Chengdao buried-hill, the Dongying formation's sealing ability is relatively poor in Gudao buried-hill, and the top of Gudao buried-hill is directly connected to the sandstones of the lowest section in the Guantao formation. As a consequence, hydrocarbon could enter into the Guantao formation through the sandstones, and therefore it is hard to form reservoirs in Gudao buried-hill. In comparison, the caprock sealing ability is favorable in Chengdao buried-hill, providing effective places for hydrocarbon accumulation and availing the formation of reservoirs.