A study on hydrocarbon generation potential of deep source rocks and gas sources in Changling Fault Depression,Songliao Basin

Through natural gas exploration in the Changling Fault Depression,abundant natural gas flows were obtained and high-quality source rocks were also reveiled.Based on bulk analyses,organic matter abundance,organic matter type and thermal maturity of the source rocks were studied systematically.At the same time,gas gener-ating intensity and gas generating quantity were quantitatively analyzed by using basin modeling technologies.The results indicated that gas source rocks of the Shahezi Formation are characterized by abundant organic matter and dark mudstone distributions and high-over thermal maturity.They possess high gas generating intensity with the biggest value surpassing 500×108 m3/km2,and large gas generating quantity,accounting from 74.40% of the total amount.The Yingcheng Formation has good gas-source rocks with moderate dark mudstone and relatively high organic matter.It has type-Ⅲ organic matter and low-over thermal maturity.The gas generating intensity is moderate,between 20×108 and 60×108 m3/km2.The gas generating quantity is 13.63% of the total amount.The Huoshiling Formation has relatively good source rocks with limited dark mudstone and low organic matter.It has type-Ⅲ kerogen and over-thermal maturity.The gas generating quantity is 7.10% of the total amount.The Denglouku Formation has poor-gas source rocks,and is characterized by undeveloped dark mudstone and low organic matter abundance.It has type-Ⅲ organic matter and low-high thermal maturity.Hydrocarbon gases in the Changling Fault Depression mainly originated from the Shahezi Formation,and secondarily from the Yingcheng Formation.The contribution of the Huoshiling Formation gas source rocks is relatively small.

Organic Geochemical and Fluid Inclusion Evidence for Filling Stages of Natural Gas and Bitumen in Volcanic Reservoir of Changling Faulted Depression,Southeastern Songliao Basin

Recently,volcanic gas reservoirs in Yaoyingtai （腰英台） and Daerhan （达尔罕） tectonic belts in Changling （长岭） faulted depression of southeastern Songliao （松辽） basin have been discovered.Based on the compositions and isotopic values,the natural gas is characterized by high content of methane,low content of C2＋,and C1/C1-5 beyond 0.95.Also,the natural gas contains nonhydrocarbons including carbon dioxide with the content from 20% to 40% and minor amount of N2.Combined with the isotopic values,the natural gas is generated by humic kerogen and coal-derived type,but in Daerhan,the natural gas is probably mixed by oil type gas.From the measurement of lithology and fluid inclusions in volcanic rocks,the bitumen,liquid hydrocarbon,and gas hydrocarbon inclusions are present.Through the analysis of the single gas inclusion in volcanic reservoir,the content of carbon dioxide is low,so the carbon dioxide and hydrocarbon gas of the reservoirs are not accumulated at the same time.In addition,minor amount of bitumen in the reservoirs is formed by thermal evolution of the crude oils sourced from the Yingcheng （营城） Formation mudstones through the characterizations of the biomarkers.The distribution of homogenization temperatures presents two peaks,one with the liquid hydrocarbon filling stage,and the other with gas filling stage.However,in Daerhan tectonic belt,the second peak is gas and carbon dioxide mixed filling period probably.Combined with the homogenization temperatures of salt water inclusions,the oil and gas filling period is from Qingshankou （青山口） Formation to Nenjiang （嫩江） Formation in the research area.During the charging period,minor amount of inorganic carbon dioxide filled into the trap,but plenty of inorganic carbon dioxide from the end of Sifangtai （四方台） to Eogene periods was related with the structural movement.