Geochemical Characteristics And Comparison Of T₃-K Source Rocks In The West And Middle Sichuan

Sichuan basin, a sedimentary basin, contains the biggest amount of nature gas throughoutChina. According to the last three resource surveys, the reserves of nature gas in Sichuanbasin reach53477.4×108m3. By the end of2004, more than100drilled gas wells with nearly70gas structures, which contain a reserve of8750×108m3of recoverable gas, have beendiscovered. In this basin, there are six kinds of source rock, namely, T₃P21, P1+2, S1,∈1andZ2. Furthermore, hydrocarbon source rocks, which have been discovered in Jurassic, are thepotential source of hydrocarbon source. It is seen that this basin is abound with hydrocarbonsource rocks. This provides a solid foundation of study in natural gas accumulation. Thepresent study focuses on the upper Triassic xujiahe, Jurassic and cretaceous strata. The upperTriassic xujiahe hydrocarbon source rocks are mainly distributed in T₃x1, T₃x3, T₃x5.Hydrocarbon source rocks can be found in the whole basin, whose amount decreases fromwest to east. Jurassic hydrocarbon source rocks are mainly distributed in the lower Jurassicliang mountain group and the artesian well group. In the centre area, it has a good condition togenerate oil and gas and this is not so in the peripheral region. The hydrocarbon source rocksis vary rare in cretaceous because of the eroded formation.For the distribution of hydrocarbon source rocks in these three sets of the strata, a lot ofwork has been done in the past. However, no comparison is made on the geochemicalcharacteristics of hydrocarbon source rocks in the west and middle Sichan basin. In fact, sucha comparison is of practical significance. To this end, review and comparison on thegeochemical characteristics of T₃-K hydrocarbon source rocks in the aforementioned areas aremade in this study through the method of the earth chemical analysis. In specific, this paperconsists of the following items:（1）Richness of organic matter in T₃-K source rocks in the west and the middle Sichuanbasin: on the basis of the sample data along with the distribution of hydrocarbon source rocks,researches on three aspects of the organic matter abundance in T₃-K source rocks, namely theorganic carbon content （TOC）, chloroform bitumen "A" and organic matter pyrolysisparameters are carried out.（2）Organic type of T₃-K source rocks: Four aspects of the hydrocarbon source rocks, i.e.,cheese root of the elements, kerogen microscopic components, chloroform bitumen "A" racecomponents and rock pyrolysis parameters have been studied. （3）Organic matter maturity have been analyzed via vitrinite reflectance （Ro）, rockpyrolysis parameters, normal alkanes parity advantage of the hydrocarbon source rocks（4）Comparison is made on the saturated hydrocarbons chromatographic characteristics ofhydrocarbon source rocks from various regions.（5）In view of T₃-K source rocks’ characteristics, organic carbon content change, thethickness distribution and mature evolution of the hydrocarbon source rocks, standards andmaps of classification and evaluation for hydrocarbon source rocks in Sichuan basin arepresented.