A typical Cambrian oil reservoir: Origin of oil reservoir in Well TZ62, Tarim Basin

Abstract

The distribution of the Silurian asphaltic sandstones is very widespread in Tarim Basin. After the oil derived from Cambrian entered into the Silurian reservoir, the regional uplift of the crust destroyed the oil reservoir. It is not sure whether the Cambrian source rocks or the Middle and Upper Ordovician ones or both of them made contributions to the organic matters in the Silurian asphaltic sandstones. The chemical compositions of oil and oil-source rock analysis from Well TZ62 show that its sterane and terpane compounds possess the characteristics of Cambrian source rocks, indicating the oil from Well TZ62 was derived mainly from Cambrian. On the other hand, the sandstone lens in Well TZ62 was well trapped by the Silurian mudstone; therefore the oil reservoir in Well TZ62 has a good preservation condition, and was difficult to be filled by the later formed Middle and Upper Ordovician hydrocarbons. Accordingly, the Silurian oil reservoir in Well TZ62 is an ancient reservoir that was degraded slighter and preserved better than others. Among the reservoirs discovered in Tarim Basin, the oil reservoir in Well TZ62 is the first integrally preserved Silurian oil reservoir.