Geochemical features and genesis of the natural gas and bitumen in paleo-oil reservoirs of Nanpanjiang Basin, China  

作　　者：ZHAO MengJun ZHANG ShuiChang ZHAO Lin DA Jiang 

机构地区：[1]Research Institute of Exploration and Development,PetroChina,Beijing 100083,China [2]Guizhou Institute of Petroleum Geology,Southern Petroleum Exploration and Development Corp.,Sinopec,Guiyang 550000,China

出　　处：《Science China Earth Sciences》2007年第5期689-701,共13页中国科学（地球科学英文版）

基　　金：Supported by the Sinopec Project (Grant No: P00045);the National Science & Technology Project for the 10th Five-Year Plan (Grant No. 2001BA605A-06)

摘　　要：Bitumen from the Nanpanjiang Basin occurs mainly in the Middle Devonian and Upper Permian reef limestone paleo-oil reservoirs and reserves primarily in holes and fractures and secondarily in minor matrix pores and bio-cavities. N2 is the main component of the natural gas and is often associated with pyrobitumen in paleo-oil reservoirs. The present study shows that the bitumen in paleo-oil reservoirs was sourced from the Middle Devonian argillaceous source rock and belongs to pyrobitumen by crude oil cracking under high temperature and pressure. But the natural gas with high content of N2 is neither an oil-cracked gas nor a coal-formed gas generated from the Upper Permian Longtan Formation source rock, instead it is a kerogen-cracked gas generated at the late stage from the Middle Devonian argilla- ceous source rock. The crude oil in paleo-oil reservoirs completely cracked into pyrobitumen and methane gas by the agency of hugely thick Triassic deposits. After that, the abnormal high pressure of methane gas reservoirs was completely destroyed due to the erosion of 2000--4500-m-thick Triassic strata. But the kerogen-cracked gas with normal pressure was preserved under the relatively sealed condition and became the main body of the gas shows.Bitumen from the Nanpanjiang Basin occurs mainly in the Middle Devonian and Upper Permian reef limestone paleo-oil reservoirs and reserves primarily in holes and fractures and secondarily in minor matrix pores and bio-cavities. N2 is the main component of the natural gas and is often associated with pyrobitumen in paleo-oil reservoirs. The present study shows that the bitumen in paleo-oil reservoirs was sourced from the Middle Devonian argillaceous source rock and belongs to pyrobitumen by crude oil cracking under high temperature and pressure. But the natural gas with high content of N2 is neither an oil-cracked gas nor a coal-formed gas generated from the Upper Permian Longtan Formation source rock, instead it is a kerogen-cracked gas generated at the late stage from the Middle Devonian argillaceous source rock. The crude oil in paleo-oil reservoirs completely cracked into pyrobitumen and methane gas by the agency of hugely thick Triassic deposits. After that, the abnormal high pressure of methane gas reservoirs was completely destroyed due to the erosion of 2000–4500-m-thick Triassic strata. But the kerogen-cracked gas with normal pressure was preserved under the relatively sealed condition and became the main body of the gas shows.

关 键 词：source ROCKS paleo-oil reservoir PYROBITUMEN kerogen-cracked gas Nanpanjiang Basin 

分 类 号：P618.13[天文地球—矿床学]