HYDROCARBON FILLING HISTORY OF SX OIL FIELD, CENTRAL ZHUNGER BASIN, NORTHWEST CHINA

摘要

Two core samples described in this paper were collected from Carboniferous volcanic reservoir rocks and Triassic sandstone reservoir rocks respectively from this oil field. According to hydrocarbon fluid inclusion dating, paleo hydrocarbons began to charge both reservoirs during the Middle-Late Jurassic Period.Detail compositional analysis of hydrocarbons in open pores, closed pores and hydrocarbon inclusions hosted in carbonate veins of volcanic reservoir rocks indicated dramatic variations of biomarker (terpanes and steranes) distributions. In open pores, terpanes are mainly tricyclics, but nearly no pentacyclics. It indicates very high maturity (post mature) of the current reservoired hydrocarbons. In contract, in closed pores, relative abundance's of pentacyclic terpanes are much higher than tricyclic terpanes, and isomerization parameters of C29 steranes are also relatively lower, not reaching the equilibrium values. It indicates only moderate maturity oils charging the reservoir during the early stage of the hydrocarbon filling process. The maturities of hydrocarbon inclusions hosted in carbonate veins are relatively higher than that of hydrocarbons in closed pores, but much lower than that of hydrocarbons in open pores (current reservoired oils) based on terpane and sterane parameters, probably around Ro% 1.0. Similar changes occur in Triassic sandstone reservoir rocks, thermal maturity of free hydrocarbons in intergrain pores (current reservoired oils) is much higher than those of adsorbed hydrocarbons closely by grains and clay minerals, and hydrocarbon inclusions hosted in grains.