Evidence of Multi—Stage Hydrocarbon Charging and Biodegradation of the Silurian Asphaltic Sandstonesin the Tarim Basin,China

Evidence of multi-stage hydrocarbon charging and biodegradation of the Silurian asphaltic sandstones in the Tarim Basin, China

Asphalts distributed widely in the Silurian sandstones of the Tarim Basin include dry asphalt, soft asphalt and heavy oil. These asphaltic sandstones underwent multi-episodic sedimentary and tectonic events, and their occurrence is diverse and complex, being mixed with normal oil usually. So far, very little work has been done on the asphaltic sandstone origin and hydrocarbon charging ages. After detailed study on the Silurian sandstones, the following highlights were obtained from the analytical results: distribution of the mixed asphalt, heavy oil and normal oil in the Silurian sandstones is the result of multi-stage hydrocarbon charging from the Lower Paleozoic marine source rocks; the characters of asphalts formed from oils of different charging ages are of difference; the most important process constraining the asphaltic sandstone origin is thought to be biodegradation. This paper was financially supported by funds of Petroleum & Natural Gas Exploration in the Tarim Basin from the “State 9th Five-Year Plan Period” Key Scientific Project (No. 96-111).