Study of brittleness of tight reservoir and its effect on natural fractures is of great significance to quantitative prediction of natural fractures in tight reservoirs.This paper summarized more than 20 brittleness testing methods

focusing on the development and application of brittleness evaluation methods for unconventional oil and gas reservoirs.Moreover

it also evaluated the brittleness characteristics of tight reservoir and its effect on natural fractures in the Chang 7 tight reservoir in Longdong area of Ordos Basin.The results show that several groups of high angle structural fractures are developed widely in intervals of various lighologies in the Chang 7 reservoir in Longdong area.Sandstones show the highest brittleness

followed by shaly sandstones

and mudstones has the lowest brittleness.The brittleness decreases with the increase of shale content.On the specific paleo-structure stress background

rock brittleness controls the development characteristics and development degree of natural fractures.There is a brittleness threshold

above which high angle fractures are more likely to develop

while below which it is likely to develop low angle fractures.Brittleness also controls rock fracturing ability.When brittleness index is large

rock is easier to fracture under the structure stress

resulting in more fractures.In contrast

when it is low

rock deforms instead of fracturing

thus fractures are poorly developed and even not developed.