| The Qaidam Basin is located in the northeast part of the Qinghai Tibet Plateau.It belongs to the Tarim and Sino Korean plate.It is an important oil and gas basin in Northwest China.The Tuanyushan area is located in the northwest fold belt of the northern margin of the Qaidam Basin.The upper part of the Qaidam Basin formation relatively complete,and its oil bearing strata are mainly from Shimengou formation of middle Jurassic.Work done in the past,the exploration targets for the strata were mainly coal resources,and the exploration degree of oil shale in the area was relatively low.Therefore,it is particularly important to study the distribution regularity of oil shale and the prediction of resource potential in the whole area.This study is based on the description of the outcrop in the study field and the core observation of QCD-1 well and QCD-2 well,with analyzing of well logging curve and the grain size analysis under the microscope,the oil shale formation of the Shimengou formation in the Tuanyushan area of the northern margin of Qaidam can mainly divided into delta facies and lake facies.On the basis of this,further seven sedimentary subfacies and twelve sedimentary microfacies are divided.The delta facies is mainly located on the southwest side of the study area,reflecting the main provenance areas in the study area.In the upper shale section of the Shimengou formation,the semi deep lake-deep lake subfacies dominated,and it is the mainly development facies with oil shale Developed.The oil shale in the study area is mostly black gray and dark gray,develops horizontal bedding and massive structures.According to the sampling and testing of oil shale samples in QCD-1 well and QCD-2 well,the Shimengou formation developed 11 layers of oil shale.The upper shale section has three layers of oil shale,which has a large thickness,good continuity and extensive development in the area.The accumulative thickness of the oil shale is 8.31 m,the oil content is 5.50~6.29% and the average is 5.73%.It is a medium quality oil shale with high ash,medium heat and low sulfur.The type of organic matter is type I and II1,and the lower coal bearing section develops 8 layers of oil shale.The accumulative thickness of shale is 14.7 m,the oil content is 4.09~7.83% and the average is 5.47%.It is a medium quality oil shale with low ash,high calorific value and low sulfur.The type of organic matter is type II2.According to Single well facies and characteristics of depositional sequence,combining logging sequence and rock assemblage,now the sequence stratigraphic framework of the Shimen gully formation in the Qaidam mountain area is established.Two third-ordersequence,sequence I and II,are developed in the study area,and oil shale mainly occurs in the Water inlet system and high water system of sequence II.Oil shale has obvious logging response characteristics with high acoustic logging information,High resistivity logging and low natural gamma-ray logging,Two high and one low logging response on the log curve,and he oil shale content in the region has a good linear relationship with TOC According to this,the oil shale identification model can be established by the delta LOGR method and the oil shale TOC can be predicted quantitatively,and the oil shale distribution in the area can be deduced.The volume of oil shale resources is predicted by volume method.According to the predicted results,the oil shale is mainly distributed in the middle area,northwest and southeast parts of research region,and the buried depth is generally less than 1000 m,the accumulative thickness of oil shale is between 6~20 m.Oil shale prediction resource is 1.8 million tons,and oil shale oil prediction resource is 0.12 million tons.The oil shale of coal section has higher oil content but thinner thickness,poor transverse continuity and has no resource potential.This result has a certain guiding significance for further exploration of the oil shale in study area. |
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