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Abstract Fracture toughness of rock is one of the most important factors for evaluating the fracability of shale reservoir quantitatively. Based on straight seam grooving Brazilian disc test(SNBD)，fourteen shale pieces taken from Longmaxi Formation have been tested to measure fracture toughness of both type I and II. And by using the above results，combining with the logging data where the cores locate，the paper makes a regression of the shale fracture toughness with the data of density，acoustic time and GR logging. Comparing previous prediction model based on tensile strength，a direct relationship between fracture toughness and geophysical logging data was established in this paper. According to the prediction model，fracture toughness of organic-rich shale is proportional to the density and interval transit time of rock，while inversely proportional to its shale content. The more total organic carbon(TOC) or clay mineral is， the smaller fracture toughness is，it is more easily to extend forward after crack initiation. The results indicate that the fracture toughness of predication model has a pretty good correlation with that measured by SNBD. This paper can provide important theoretical basis for engineering design process to identify“Sweet Spots”.
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2015, Vol. 34 
