Abstract: The shale oil reservoirs are characterized by low oil and gas abundance,poor permeability,no natural productivity or lower natural production capacity in single wells compared with the lower limit of commercial oil flow,and fast energy decay,etc.The application of efficient volumetric fracturing technique to horizontal or multi-lateral wells is the key to achieving efficient development of shale oils.In order to evaluate the fracability of the shale oil reservoir in the Lucaogou Formation in Jimusaer sag,sufficient experimental and theoretical studies were carried out.The characteristics of deformation and failure,mechanical strength and their lateral variations in the Lucaogou oil-bearing reservoir in Jimusaer sag were recognized.And a new method for evaluating the fracability indexes was established based on the analysis of the factors influencing the shale reservoir fracability in the Lucaogou Formation.The results show that due to the significant brittleness of shale under deformation and the well development of fabric planes such as bedding and micro-fractures,the intrinsic geological and mechanical conditions of the Lucaogou Formation are favorable for the formation of complex fracture networks under fracturing.There are interlayers characterized by high rock mechanical strength and in-situ stress in the Lucaogou shale reservoir.Therefore,to maximize the effective volume of fracturing in such reservoir,the artificial fractures should be designed to increase the connectivity between upper and lower reservoirs,while the fracture networks should be as complicated as possible.Besides,a new fracability evaluation method was established using brittleness index,horizontal stress difference,interlayer stress difference and fracture ductility,which can simultaneously characterize the ability of volumetric fracturing network in horizontal wells and the vertical connectivity of artificial fractures.The analysis based on microseismic fracturing monitoring shows that the fracability index evaluation method is very suitable to evaluate thin alternating shale formations typically shown in the oil shales in Jimusaer sag.

Key words: brittleness, fracability index, volumetric fracturing, rock mechanics, shale oil, Lucaogou Formation, Jimusaer sag, Junggar Basin