Mud Logging Evaluation And Resource Potential Analysis Of Shale Oil In Sanzhao Sag,Northern Songliao Basin

It has huge reserves of resources on unconventional oil especially shale oil in the northern Songliao Basin,which is the key point of exploration and development of Daqing Oilfield,and also the advantageous resource support for the construction of century-old oilfield.In this paper,from the perspective of logging evaluation,the development types of shale oil reservoirs&hydrocarbon source rocks development situation in the northern Songliao Basin were studied by using the shale oil"four properties and one quality"evaluation method.At the same time,the logging data acquisition and evaluation methods which fit for unconventional oil are optimized,and the qualitative and quantitative interpretation and evaluation models are established,in order to find favorable reservoir development characteristics and"dessert area"of shale oil,which will provide accurate&timely geological basis for exploration and development decision-making.By several wells of mudlogging exploration practice on shale oil,the application and improvement methods of comprehensive mudlogging methods are systematically summarized.By describeing cuttings and core delicately,combining with element and XRD analysis,the lithology of Qingyi section is divided into mudstone facies,shale facies,dolomite facies,shell limestone facies and siltstone facies from mudlogging data.Meanwhile,the characterization method of reservoir brittleness is determined.Based on the analysis of geochemical logging,the correction and application methods of residual organic carbon TOC value in water-based and oil-based drilling fluid logging conditions are studied,and the identification method of gas measurement anomaly is improved,which improves the accuracy of the implementation of formation oil-gas properties.Combineing with the lithology and geological characteristics,a comprehensive logging evaluation method of"four qualities and one quality"is proposed for shale oil in the study area.That is,reservoir property,oil-bearing property,fluidity,compressibility and quality of hydrocarbon source rock.Also the study area is evaluated by comparison method and single well analysis methods.The specific evaluation methods include all as follow:Shale oil reservoir property is described by mudlogging cuttings and core lithology and physical properties;The oil-bearing property is described by gas-logging data,core conditions and geochemical logging analysis data;The fluidity is described by permeability,formation pressure and crude oil properties;and the compressibility of land acquisition layer is characterized by the content of brittle minerals from XRD logging datad.The quality of hydrocarbon source rocks is evaluated from five models such as the types,abundance and maturity of organic matter.Combining the method of"four qualities and one quality"shows that the shale oil mainly development in Qingyi section.which has good oil-bearing property,good fluidity and good reservoir property,and poor compressibility,and the quality of hydrocarbon source rock is good on Sanzhao Sag.It has good hydrocarbon generation capacity,which is the"dessert"area of the vertical.Through the introduction of favorable coefficient of shale oil geological"sweet spot",the comprehensive score of shale oil reservoir forming factors is carried out,and the vertical"sweet spot"is quantitatively evaluated,so as to give more specific suggestions for selecting fracture layer and oil testing.According to the results of comprehensive logging,the evaluation criteria of vertical high-quality shale oil in the study area are divided,which will provides important first-hand basic geological data for shale oil exploration in furture.The comprehensive study shows that the Sanzhao sag in the north of Songliao basin has the geological basis of shale oil accumulation and has the possibility of forming industrial oil flow.The favorable areas maily develops dark shale,better than fluorescence level,abnormal amplitude value of gas logging more than 2 times,effective porosity greater than4%,fracture development medium,TI value of mudstone greater than 80 mg·HC/g·C,S₁greater than 2,the Ro is greater than 1%,the TOC is greater than 2%,the Tmax is greater than 450°C,the Ro is greater than 1,the brittleness index greater than 30%,the pressure coefficient is greater than 1.3.Preliminary evaluation of the"sweet spot"area of about320km² in the first layer of Qingyi formation in the central depression,the resources is about 2.65～3.51×10⁸ tons.