Research On The Recognition And Resource Evaluation Of The Upper Cretaceous Oil Shale Based On Geochemistry-geophysics Technique In The Songliao Basin (NE,China)

The Songliao Basin is the huge depression Cretaceous basin with rich oil shale resource in China,which is developed during the depression stage of the Upper Cretaceous Qingshankou (K2qn) and Nenjiang(K2n) Formations. However, it presents the characteristics of higher exploration in the local and lowerrecognition in the global with the oil shale resource in the Songliao Basin. In this thesis, on the basis ofabundant test data and geophysical data especially the valuable organic geochemical data are obtained fromAustria during the period of my abroad study, the methods of geochemistry and geophysics as the mainguide, researched the oil shale characteristics of rock mineral, geochemistry and geophysicsits, anddiscussed which were the main factors controlled by the metallogeny and enrichment of oil shale in thehuge depression basin, which will provides an excellent basis to recognize and evaluate the resource of oilshale in the Songliao Basin.Oil shale is a diverse group of rocks, that contain mineral matter and organic matter. The total organiccarbon (TOC) contents vary between 5.0 and 12.0 wt.%, and it presents the predominance of type-I kerogenin the oil shale sequence of the Songliao Basin. The maturity of OM are regular increases with thedeepened depth. The OM of oil shale is dominated by lamalginite and telalginite, which may be theindicator of the aquatic organisms. The changing telalginite/lamalginite ratio may indicate changes in thealgal-microbial communities during the stage of oil shale depression. Moreover, it presents the differentcontribution to the OM by algal-microbial communities due to the predominance of Lamalginite in thestages of K2qn1and K2n1but the predominance of telalginite in the stage of K2n2. Meanwhile, thedevelopment of algae-rich laminae indicates intermittent algal blooming during the oil shale depression,which is argued for algae predominance by the outlined biomarker data of high contents of4-Methylsteroids, steroids/hopanoids ratios, and regular steranes (C27+C28)/C29ratios. Lots of studies haveshown that the clay is an important carrier of OM enrichment. The oil shale contains abundant clayminerals in the Songliao Basin, and the clay mineral contents of the K2n2stage present more predominancein comparison to the stages of K2qn1and K2n1during the oil shale depression. Morevoer, the clay mineralscontain more composition of illite and illite mixed layer. The positive correlation is represented betweenclay minerals and OM.The geochemical parameters of the oil shale in the Songliao Basin present the geological significance.By the analysis of the parameters of Rb/Sr ratios, Th/U ratios that indicates the paleoclimate, the finelyevolution characteristic of paleoclimate is reconstructed during the depression of the K2qn and K2n in theSongliao Basin, and the oil shale sequence develops during the period of warm-wet. By the analysis of the parameters of TOC/S ratios, gammacerane index, MTTC ratios, aryl-isoprenoids contents, and Sr/Ba ratiosthat indicates the paleo-salinity, the finely evolution characteristic of paleo-salinity is reconstructed duringthe depression of K2qn and K2n in the Songliao Basin, and the oil shale sequence of the K2qn developsduring the environment of semi-saline water, but it represents lower salinity in the period of the K2n1especially K2n2. The redox conditions are indicated the similar evolution characteristic with the salinity bythe parameters of Pr/Ph ratios,β-carotane contents, and V/Ni ratios, which reflects the high salinity willincrease the redox conditions. The water oxygen contents within the K2n2is higher in comparison to theK2qn1and K2n1.The analysis of the metallogeny and enrichment of oil shale is the basis to recognize and evaluate theresource of oil shale in the Songliao Basin. The metallogeny and enrichment of oil shale in the SongliaoBasin is the results of comprehensive effect by the geological factors of paleotectonic, paleoclimate anddepositional environment. The different geological factors play different role in different stages of OMevolution by the research of the evolution of metallogeny and enrichment of oil shale in the Songliao Basin.The oil shale of both the K2qn and the K2n are developed under the environment of semi- anddeep lacustrine controlled by fast tectonic subsidence and warm-wet climate. The advantages of the K2qnare the OM source of algal predominance, the water substances with higher salinity and strongerreducibility, low dilution by terrigenous detrital mineral matter, and lower maturity. However, the algalblooming play a leading role within the K2n, but the preservation conditions, the dilution of mineral matterand maturity play a secondary role.The oil shale in the Songliao Basin exhibits the logging response with low density, high acoustic traveltime, high-neutron porosity, high-natural gamma, and high resistivity of the"four-high and one-lowcharacteristics", and seismic response with higher frequency, medium–high amplitude, and low impedanceseismic reflection structure. On basis of the different contribution to the logging response due to diversegroup of oil shale rocks, the different equivalent rock-physics models are constructed in this paper, and wehave derived the different logging response equations of oil shale in the theory, which show that the densityresponse of oil shale is depended primarily on the relative content between OM and heavy mineral, the(acoustic travel time, neutron porosity and natural gamma density) responses of oil shale are dependedprimarily on the relative content between OM and caly mineral, the resistivity response of oil shale isdepended primarily on the relative content among wet caly, OM and heavy mineral. On basis of theassumption of monolayer coating, we firstly propose the view that the OM substituting clay pore waterchanged the"fluid property"of clay pore. The substituting process can be divided into three period ofunder substitution, balanced substitution and over substitution, and the over substitution leads to thesignificantly worse conductivity of oil shale with enrichment OM. Therefor, we reinterpretate intrinsicconductivity mechanism of logging response with high resistivity of the oil shale in comparison tomudstone. Meanwhile, the seismic response of oil shale is mainly depended on the change of elasticparameters caused by"high OM"substituting"fluid property". The result of forward modeling indicatesthe seismic of study area can distinguish the minimum thickness of 6.4 meter from oil shale.To improve exploration efficiency and save on exploration costs, the integrated geophysical techniques are incorporated into the evaluation system of oil shale in this paper. The quantitative evaluation of thesingle-well of oil shale with log-seismic multi-attributes is carried out. The join of multi-attributesespecially seismic attributes can be avoided the influences of formation factors. The convolution factoralgorithm could eliminate of the frequency difference between well log and seismic and incorporate(Nwi–1)×n low-error attributes, and the accumulated average error of predictive TOC (0.293%) is less thanthe error of△l ogR(0.995%). Therefor, this method improved the precision of TOC prediction andcontinuously compensated the background values for TOC in the vertical. Meanwhile, a method for thespatial quantitative evaluation of oil shale was proposed using the seismic technique. TOC>5.0 wt % andOY>3.5 wt % was taken as the criteria for the quantitative evaluation of oil shale. According to theevaluation results, the inversion volume of wave impedance obtained through the sequence-log constrainedseismic inversion method enables the qualitative evaluation of the spatial distribution of oil shale; theinversion volume of TOC and oil yield enables not only the qualitative prediction of the spatial distributionof oil shale, but also the quantitative evaluation of the quality features of oil shale.In order to realize the evaluation of the oil shale potential resources in the large depression of SongliaoBasin, the statistical analogy is employed which combine main geological analogy with statisticalalgorithms supplemented. Three large oil shale deposits of Fuyu-Changchunling, Qianguo-Nongan andShenjingzi with high exploration in the Songliao Basin are selected as the calibrated area. Main geologicalparameters are optimized in terms of the metallogeny and enrichment mechanisms of the oil shale,including paleotectonic, paleoclimate, depositional environment, water salinity, redox condition, input ofterrigenous mineral matter, type of OM, maturity of OM, abundance of OM, which are as the data source ofgeological analogy parameters library of different oil shale target intervals. Meanwhile, a method ofcharacteristic factor is utilized to calculate the analogical coefficients between the calibrated area andpredicted area, and monte-carlo method and combination of sampling method are used to estimate oil shaleresources. Therefore, the statistical analogy is a promising approach to evaluate oil shale resources ofmiddle-low exploration basin, and it will bring the estimate with successful hold. In this paper, we firstlypropose the principle of"high probability value with fluctuated remarkably"to reasonable choice of theprobability range of potential oil shale resources, and the oil shale resources from the probability ranges of100% to 85% are taken as the reasonable result of oil shale resources evaluation in the Songliao Basin. Theresults show that the resources of middle-shallow layer oil shale are 391.71 gigaton (100%), 460.76 gigaton(95%), 516.59 gigaton (90%), 575.05 gigaton (85%), respectively, which all outclass the oil shale resourcesof 323.65 gigaton from the first"National oil shale evaluation". The increase of the potential oil shaleresources mainly dues to improve of oil shale resources exploration, improved method of resourceevaluation, improve recognition of oil shale of predicted area, which indicate the results of resourceevaluation will change with the improvement of exploration and evaluation method.