Experimental Research On Physical-mechanical Properties And Brittleness Evaluation Of The Shale Reservoir In North-west Hunan Province

As the global economy growing rapidly,the demand for energy continues to rise.Shale gas is a new clean energy that widely distributed,its development has attracted the attention of many countries.At present,the main way of exploitation of shale gas is the fracturing of shale gas reservoir;the physical-mechanical properties of shale gas reservoir has significant influence on its fracturing,and the brittleness evaluation of reservoir is one of the key content of the fracturing evaluation;therefore,it has important theoretical value and practical significance to carry out the research of physical-mechanical properties and brittleness evaluation of shale gas reservoir on shale fracturing evaluation and the breakthrough of the technical bottleneck that developing shale gas in our country.In this paper,Cambrian Niutitang shale reservoir of Northwest Hunan Province is taken as the research object.Through the investigation of geological data and the scouting of the site,the basic stratigraphic characteristics of area where the shale reservoir lies were known;by applying weighing method,the density and moisture content of shale in the dry,natural and saturated status were measured and analyzed;by using X-ray powder diffraction meter to carry out X diffraction experiment,the mineral constituent of shale reservoir were analyzed;mineral crystal appearance and pore structure characteristics of shale were observed and analyzed by using scanning electron microscopy;by using RYL-600 shear rheometer and RMT-150 B rock mechanics testing machine to carry out uniaxial compression test,triaxial compression test and splitting test,strength and deformation characteristics of shale with different moisture state under uniaxial compression were obtained and analyzed;strength and deformation characteristics in the condition of triaxial compression(confining pressure were 10 MPa,25MPa and 40MPa)were obtained and analyzed;and the strength and deformation characteristics of the shale in the condition of splitting were obtained and analyzed.Based on the investigation and the analysis of the brittleness evaluation methods at home and abroad,the brittleness of the shale reservoir was evaluated by using different brittleness evaluating index combining the test data obtained in this paper,and the evaluation results were compared and analyzed.About the shale reservoir,the results show that :(1)The structure is compact,the natural water content is low and the saturated water content is lower than 1%.The content of brittle minerals is relatively high,the clay minerals content is relatively low,and the micropores and microcracks are relatively developed(2)The uniaxial compressive strength is 102.54 MPa on average,the average young's modulus is 27.85 GPa,Poisson's ratio is 0.23 on average;with the increase ofwater content,the strength of axial compression is reduced,and the Poisson's ratio is increased;the failure strain of uniaxial compression is 0.32% ~ 0.74%,the shale burst to failure right after peak strength.With the increase of confining pressure,the strength of shale increase,the young's modulus increased also;failure mode under triaxial compression are mainly single shear failure and splitting failure,the ratio residual strength to peak strength is low.In the condition of splitting,the strength is11.7MPa on average,when reaches its peak strength,the shale fails rapidly with no residual strength remains.(3)Different brittleness evaluation methods leads to different results,the conclusion that the brittleness of Niutitang shale reservoir in northwester of Hunan province is good and the reservoir is suitable for fracturing are obtained by comparing and analyzing all the evaluation results comprehensively.