The Comprehensive Experimental Research For Brittleness Evaluation Of Anisotropic Shale Reservoir

As the augmenting demand of energy resources?conventional oil recovery is increasingly difficult,and the new technology in geophysical prospecting makes extracting oil and gas in shale significant in researchers' eyes.Shale is tight with low porosity and permeability which means that effective hydraulic fracture method is needed to change the seepage property for satisfying the standard of commercial exploitation.Researches shows that brittleness of the reservoir rock directly related to its compressibility.Therefore,great efforts were paid on the evaluation of rock brittleness,as it is an indispensable procedure before hydraulic fracture of the reservoir bed.Many theories to characterize rock brittleness have been put forward mostly based on rock strength,full stress-strain experiment and rock hardness.However,those theories are stem from different disciplines,a unanimous standard to evaluate rock brittleness has not been obtained and the applicability of some of those theories lacks further test.Richman method which is the most common description of rock brittleness by using elastic moduli for characterization.In order to measure elastic moduli of the rock including Young's moduli and Poisson ratio more accurately,fiber grating sensor was introduced into the experiment and realized the selection of optimum size of the samples.Through four rock samples simultaneously uniaxial compression test and ultrasound speed test to achieve static and dynamic measured ratio versus with theory ratio,and verified fiber grating also has high-precision in the rock strain test.Based on the number of tight oil shale properties,mechanical characteristics,mineral composition and other parameters of the test,and brought them into existing brittle formula,then analysised formula applicability and discussed the parameters relationship with others,finally proposed a full evaluation of the brittle new formula,which containing the mineral composition,the elastic parameters and parameters characteristics post-failure.