Study On Rock Mechanical Properties And Fracability Of Deep Shale Oil Reservoir

The deep shale oil of Fengcheng Formation in Mahu sag is an important exploration field in Junggar Basin in recent years.In order to effectively evaluate the shale oil reservoir of Fengcheng Formation,determine the rock mechanical characteristics of the reservoir and the ability of hydraulic fracturing to form complex fracture network,this paper takes the shale oil reservoir of Fengcheng Formation of M1 well in Mahu sag as the research object,and systematically obtains the rock mechanical parameters and fracture characteristics of the reservoir through rock mechanical experiments of reservoir cores with different depths and lithology.The in-situ stress profile is established and the reservoir mechanical properties are interpreted by using the logging results.The main controlling factors of reservoir fracture propagation are analyzed,and the quantitative evaluation model of reservoir fracability is established.Through the correlation analysis of acoustic emission b value,the weight value of each factor in the model is determined.The evaluation results of the fracability of the whole well section given by logging interpretation are consistent with the results of the liquid production profile of the well,which shows that the established quantitative evaluation model of fracability is reliable.It provides a reference basis for shale oil reservoir location optimization and fracturing reconstruction of Fengcheng Formation in Mahu depression.The main conclusions are as follows:(1)The mineral composition and TOC test show that the mineral composition of Fengcheng Formation reservoir is mainly quartz,feldspar,calcite and dolomite,the content of clay minerals is low,the content of brittle minerals is high,and the TOC content is lower than that of reservoirs in other areas.Porosity test and SEM scanning test show that the reservoir has low porosity and permeability,and the intergranular pores and microporous fractures are relatively developed.(2)The indoor rock mechanics test results show that the shale oil reservoir of Fengcheng Formation belongs to deep hard brittle shale,with large buried depth,high insitu stress value,high compressive and tensile strength and high elastic modulus,high rock brittleness,complex fracture shape after failure,low degree of bedding development,and fracture propagation is not affected by bedding.The dynamic and static conversion formula of elastic modulus of reservoir rock is obtained by experiment,which provides a basis for calibrating logging interpretation data.(3)The acoustic emission b value in the process of core experiment can characterize the complexity of fracture.Acoustic emission is the manifestation of core micro fracture.The energy distribution of acoustic emission events can be characterized by b value,and high b value represents more complex fractures,which can be used as the basis for quantitative evaluation of fracability.(4)The main controlling factors of reservoir hydraulic fracturing fracture propagation are comprehensively analyzed.The in-situ stress state,rock brittleness,compressive strength and natural fracture development degree of the reservoir are the main factors affecting the fracture propagation of the reservoir.Among them,high brittleness and local natural fracture development are the favorable factors for the formation of complex fracture network,and high compressive strength and high horizontal stress difference coefficient are the unfavorable factors for the formation of complex fracture network.(5)The quantitative evaluation model of fracability is established by selecting four parameters: brittleness index,crack density,compressive strength and horizontal stress difference coefficient.According to the correlation coefficient between the acoustic emission b value of rock core and each factor,combined with the entropy method,the weight value of each factor in the fracability evaluation model is determined.(6)The fracability profile is given by rock mechanics test and logging interpretation.It is concluded that the overall fracability of the reservoir is medium,and there are great differences between layers.It is in good agreement with the display results of the liquid production profile after fracturing,which shows that the fracability evaluation method is reliable.