Study On Rheological Characteristics Of Shale And Its Influence On The Distribution Of In-situ Stress

In the process of shale gas exploration and development,the problem of stratigraphic stress state changing greatly in the shale shale layer is based on the investigation project of the geostress field in the key area of the southern shale gas,combined with the core chamber creep experiment and core slice identification.In-well logging data and on-site geostress measurement methods,the creep characteristics of shale under long-term stress loading are studied,and the geostress calculation model of shale layer is constructed.The geostress of mud shale layer is proposed with depth.Estimation method of distribution.Through the shale creep experiment,the rheological parameters of the shale are determined,and then the geostress evaluation model is combined with the logging data to realize the shale gas resource distribution area.The typical borehole stress profile is established and verified by the measured data.To achieve refined research on the geostress state of shale formations,and provide basic data for unconventional oil and gas exploration and development such as shale gas.The main research contents and results of the thesis are as follows:(1)On-site ground stress measurement and applicationThe in-situ stress measurement was carried out by using the borehole-based hydraulic fracturing method and the core-based inelastic strain recovery method(ASR),and the southern shale such as the An page 1 well,the Zi page 1 well and the Andi 1 well were obtained.In-situ geostress data of gas geological survey wells,by comparing the geostress state of mud shale formation and adjacent sandstone or limestone strata in the same well,it is found that the horizontal stress difference of shale layer with higher shale content is generally lower than that of harder.Sandstone and limestone layers.At the same time,combined with borehole imaging logging,it was found that drilling induced cracks occurred in the adjacent hard sandstone and limestone layers,but there was no drilling induced crack in the shale reservoir.The results show that the shale reservoirs creep under long-term loading,resulting in a decrease in horizontal differential stress.(2)Fabrication characteristics and mechanical properties of mud shaleThe structural characteristics of the mineral components of the shale core were obtained by scanning electron microscopy.At the same time,the indoor uniaxial compressive strength compression experiment was carried out on the shale standard samples with different clay mineral content,and the stress-strain curve was obtained.The results of mechanical experiments show that the higher the clay mineral content,the lower the compressive strength of the shale.(3)Study on compression creep characteristics of shale in the chamberIn order to understand the creep characteristics of mud shale under long-term load,the core was obtained and the grading loading experiment was carried out.The loading time of each stage was about 3 hours,and the stress and strain during the creep process of the core were changed with time.curve.The data results show that during the compression and creep experiment of mud shale,the two processes of decelerating creep and constant velocity creep have been experienced,and no accelerated creep has occurred.The axial strain of the rock sample slowly increases with time and the curve shape is relatively standard,and the transverse strain versus time curve is correspondingly poor.(4)Calculation model of differential stress considering creep effect of mud shale layerBased on the core mineral content and indoor compression creep experiment,the parameters n and B which characterize the creep characteristics of the shale are introduced,and the calculation model of the formation difference stress of the shale reservoir with time effect is obtained.(5)Calculation method of geostress state with depth distribution in shaleBased on the calculation model of the formation difference stress considering the creep properties of the formation,the calculation parameter ? which characterizes the relationship between the maximum principal stress SHof the formation level and the minimum principal stress of the horizontal level is introduced,and the elastic modulus E of different depths of the mud shale layer is obtained by combining the borehole logging data.The data of the geostress state along the depth of the shale layer in the Anye-1 well are obtained.The data show that the geostress data is in good agreement with the measured geostress data.The established geostress calculation method reflecting the creep characteristics of the shale layer can effectively reduction of geostress information has certain guiding significance for future oil and gas exploration and development of mud shale formation.