| It is known that an amount of bitumen is distributed in Ordovician reservoirs in the northwest of central Tarim Basin. The analysis of the drilling cores and thin-sections from Katake-1 area to Shunxi area shows that the reservoir bitumen commonly exists within various pores (such as intragranular, intergranular, intracrystal and intercrystal pores) and fissures, as well as sutures. According to the fluorescent color, the reservoir bitumen can be divided into 4 kinds, oily bitumen, gel-bitumen, residual bituminous bitumen and carbonaceous bitumen, in which the oily bitumen and carbonaceous bitumen are common. The Ordovician bitumen probably formed during two periods, the early-forming one without fluorescence and the late-forming one with fluorescence, depended on the evident cross-cutting or packing between the two periods. It is believed that the carbonaceous bitumen with high Rb values probably is the product that derives from the early-forming bitumen that suffered from long term thermal evolution， and the fluorescent carbonaceous bitumen with low Rb values probably is the late product after hydrocarbon charging in the reservoir. |
