Evaluation of source rocks of Lower Cambrian Qiongzhusi Formation in eastern Sichuan Basin
The oil and gas system in the Qiongzhusi Formation in the Sichuan Basin from the Lower Cambrian has more than 1.3 trillion m3 of reserves,but no substantial breakthrough in this regard has been made in the region after 30 years of exploration.This study comprehensively investigates the organic geochemistry of Well Loutan 1,Well Wutan 1,Well Mashen 1,Well Jiaoshi 1,and the Chengkou profile to determine the conditions of hydrocarbon generation by source rocks in the Qiongzhusi Formation in eastern Sichuan.The results showed that the Qiongzhusi Formation in Well Mashen1 was 358 m thick,while the black mudstone at its bottom was about 130 m thick.To the north,the thickness of the Qiongzhusi Formation increased to about 400 m while that of the lower mudstone(TOC＞0.5％)decreased to 50 m.The formation was 110～150 m thick in the eastern Sichuan Basin while the lower black mudstone was about 60 m thick.Its average total organic carbon(TOC)content in the Well Mashen 1-Fucheng area of northern Sichuan was 3.39％～3.44％,while its average TOC content in the Well Loutan 1-Chengkou area of eastern Sichuan was relatively low at 0.52％～2.58％.The value of R.of the Qiongzhusi Formation around the basin ranged from 2.22％to 2.53％,while the R.of drilling in the basin was 2.57％～3.10％.Due to the depth of burial of the rock,the degree of thermal evolution increased from outside to inside the basin.We used the rate of hydrocarbon generation of black shale and the original coefficient of recovery of organic carbon to determine that the intensity of gas generation in the eastern Sichuan Basin exhibited a trend of increase from the basin to the northeast,and the intensity of gas generation in the Well Yingtan 1-Well Loutan 1 area was(10～20)× 108 m3/km2.The Chengkou area had the highest intensity of gas generation along the periphery of eastern Sichuan,with a value of 60 × 108 m3/km2.We simulated the thermal history of the typical depth of burial of wells to show that the source rocks for hydrocarbon in the Qiongzhusi Formation had begun generating a large amount of hydrocarbons in the Silurian(430 Ma),and entered the stage of gas generation in the Triassic(250 Ma).Our results showed that the two centers of hydrocarbon generation in the Bazhong-Nanjiang area and Chengkou area in eastern Sichuan were the most favorable zones of enrichment in the petroleum system of the Lower Cambrian Qiongzhusi Formation.
Qiongzhusi Formationsource rock evaluationeastern Sichuan Basinorganic geochemical characteristicsgas generation intensity
万方数据
维普
