Source Rock Geophysical Log Response Characteristic And Evaluation From The Scientific Drilling Boreholesin The Songliao Basin

The scientific drilling boreholes of the Chinese Cretaceous Continental Scientific Drilling Project in the Songliao Basin(CCSD-SK)are designed to solve multiple scientific problems,such as Cretaceous terrestrial sedimentary response of greenhouse climate changes,terrestrial sedimentary response of Oceanic Anoxic Events,large-scale development of terrestrial source rocks,and deep resources exploration of the Songliao Basin.This project was planned to drill four boreholes,and the second scientific borehole(SK-2)east is the main drilling borehole,finished with a depth of approximately 7000 m.We used various geophysical log data and core data from scientific boreholes to evaluate the source rocks of key formations,which can effectively promote the achievement of these scientific problems.Based on lithology profile from geophysical logs and cores,geophysical log response characteristics of organic-rich source rocks in the Nenjiang Formation were analyzed with conventional geophysical log and gamma ray spectral data.These characteristics are consistent with the other source rock characteristics in the Songliao Basin.Through comparing various evaluation methods of source rocks,different methods were proposed for source rocks in shallow or deep formations,based on their different geological characteristics.These proposed methods were applied to evaluate source rocks of the Qingshankou and Shahezi Formations in scientific boreholes,and the results are relatively desirable.The research results in this paper showed that the Qingshankou Formation is composed of shallow continental clay/sandstone sedimentation,and its source rocks reached maturity.The modified ?logR technique and Dual_Vsh method are the suitable ones to evaluate source rocks in the Qingshankou Formation,with well application results.The organic-rich source rocks with high TOC content distributed in the first member in the Qingshankou Formation(K qn1),distributed respectively at the depths of 1755~1771 m in Borehole SKI south(average TOC 3.76%,total thicknesses 4.26 m)and at the depths of 1646~1669 m in Borehole SKII east(average TOC 4.76%,total thicknesses 7.88 m).The dark mudstones in the Shahezi Formation developed,and are deep post-mature source rocks.The ?logR technique was further improved for post-mature source rocks in deep formation.The improved ?logR technique and log-overlay method can effectively evaluate source rocks in the Shahezi Formation.The organic-rich source rocks mainly distributed at the depths of 3478~5026 m in the Shahezi Formation of Borehole SKII east.Its TOC averages1.76% and its total thicknesses can be greater than 300 m.The geophysical log response characteristics of organic-rich source rocks in the Qingshankou Formation are typical,which can bebeneficial to establish geophysical log standard for the log evaluation of source rock in study area.The organic-rich source rocks in the Shahezi Formation are widely distributed and their total thicknesses are larger,which can provide more oil or gas resources.