Study On Rock Brittleness Characterization And Fracture Complexity Based On Acoustic Emission

The material basis for network fracturing is that the reservoir has brittleness characteristics.In this paper,the brittleness characteristics of rock fracture are studied by triaxial compression-acoustic emission test.The new brittleness index is redefined by the cumulative energy of acoustic emission,and the sensitivity is much higher to evaluate the rock brittleness by using this brittle index.The local brittleness characteristics that the rock bursts are determined according to acoustic emission location.Based on the damage mechanics point of view,the local damage index is defined,and local brittleness index is defined by the cumulative energy of local acoustic emission.The fracture complexity index is defined by complex network theory to characterize the complexity of fracture network.The topological structure of fractured fracture network is obtained according to hydraulic fracturing and acoustic emission location test,and the relationship between the brittleness of the rock and the complexity of fracture network is studied.The results are of great significance for the postfracture response evaluation and the fracturing construction optimization.The main contents of this paper are as follows:Firstly,the brittleness characteristics of rock fracture are studied by triaxial compression-acoustic emission test.It is concluded when the rock brittleness is strong,the fracture form tends to be burst fracture.While the rock brittleness is weak,the fracture form is more inclined to the progressive fracture.Secondly,the brittleness characteristic of rock is studied by acoustic emission cumulative energy.It is concluded that the stronger the rock brittleness is,the greater the maximum energy of acoustic emission is.The new brittleness index is redefined to evaluate the rock brittleness by the cumulative energy of acoustic emission,and the local brittleness characteristics that the rock bursts are determined according to acoustic emission location.Based on the damage mechanics point of view,the local damage index is defined by cumulative energy coefficient of local acoustic emission and the local brittleness index is established to evaluate the local rock brittleness.Once more,the application condition of complex network theory is analyzed,and it is found that it can be used to evaluate the hydraulic fracturing network.The fracture complexity index which represents the complexity of fracture network is established by applying the overall efficiency and agglomeration coefficient of fracture network.Finally,RFPA2 D finite element software is used to determine the optimum conditions of natural fracture and horizontal stress differences to generate fracture network,and hydraulic fracturing tests and acoustic emission location tests for different brittle rocks are carried out based on the research results.The topological structure of fractured network is obtained according to the test results,and the complexity of fracture network is evaluated by the topology structure and the fracture complexity index.Finally,the conclusions are as follows:(1)The stronger the rock brittleness is,the more complex the fracture network is.(2)The fracture network is divided into 3 categories: simple fracture network,semi connected fracture network and full connected fracture network.(3)The relationship between the local brittleness index and the local mean degree value is studied by partitioning the rock.