| The goal of the Scientific Drilling Project of Songliao Basin is to obtain continuous and complete records of Cretaceous continental sedimentary strata and reconstruct Cretaceous paleoenvironment and paleoclimate evolution history by constructing coring and well logging in two wells(four boreholes).Well logs provide scientists with in-situ,continuous and high-resolution geophysical and geochemical parameters of underground strata with thousands of meters,which makes it important archive of paleoenvironment and paleoclimate.The goal of this disseration is to accurately and effectively extract paleoenvironment and paleoclimate information from well logs.Based on the log,core and mud logging data of scientific drilling wells in Songliao Basin,we explore the log response mechanism of Cretaceous strata in Songliao Basin,extract log parameters sensitive to paleoenvironment and paleoclimate,and propose log analysis methods of extracting terrestrial strata geological information and analyzing paleoclimate and paleoenvironment.In this dissertation,Qingshankou Formation(lake sedimentary environment)and Quantou Formation(river and delta sedimentary environment)were taken as examples to investigate the effects of strata component content variation on logging responses under different sedimentary environments.The spectrum and wavelet analyses are used to identify the astronomical cycles recorded in well logs and analyze the sensitivity of log parameters to astronomically forced climate.The power spectrum decomposition analysis is used to understand the sensitivity of logging vertical resolution to cyclic signals of different thickness.Astronomical calibration and sedimentation rate estimation are performed from well logs by using 405 kyr cycles.Geochemical logs are used to analyze the paleoenvironment evolution of the depositional period of Qingshankou Formation.The main research achivements are as the following: 1)The mechanism of astronomically forced climate affecting logging response is clarified.For lacustrine sedimentary strata,formation resistivity is controlled by the contents of clay minerals and organic matter.The phase relationship between formation resistivity and paleoclimate depends on the dominant factor.For river and delta sedimentary strata,clay minerals are important bridges between logging responses and paleoclimate.In this case,log parameters controlled by clay mineral contents can be used for astronomical cycle analysis.2)A method for astronomical cycle analysis based on well logs is proposed.The analysis and continuity analysis of main controlling factors of log responses are recommended to acquire the optimized log parameters sensitive to paleoclimate.3)The Al/Ti curve from elemental capture spectroscopy logs can be used as a proxy for productivity of paleolakes.The overlapping analysis of Ca and TOC curves can be used to reveal the water depth changes of paleolake.4)A method for multi-resolution scanning detection of strata cycle signicals using array induction logging is proposed.The sensitivity of different well logs to astronomical cycles varied significantly with changes in vertical resolution.Array induction logging provides resistivity logs with various vertical resolutions.Therefore,resistivity logs with different vertical resolutions can be used for comprehensive analysis of astronomical cycles in strata,which improve the accuracy of detection.5)The electrical structure of Quantou Formation in Songliao Basin records eccentricity,obliquity and precessional cycles,which indicates that its sedimentary process is controlled by astronomically forced climate.The duration of Quantou Formation in SK-2 east borehole is approximately 5.65 Ma.This study forms a set of methods for analyzing paleoclimate and paleoenvironment based on well logs,and provides technical support for high-resolution study of paleoenvironment and Paleoclimate in the Cretaceous of Songliao Basin. |
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