| The fracturing fluid for shale reservoir hydraulic fracturing contains little proppant,thus most of the cracks don't form the effective support,and the flow conductivity of fracture network relies mainly on the shear slippage of the fracture.But at the moment the fracture type of nature fracture in hydraulic fracturing cannot be recognized.The formation and extension of micro cracks in material can be continually monitored by Acoustic emission technology in real-time.It is one of the effective methods to analyze failure mechanism of rock.The thesis focus on the rock failure mechanism of shale in hydraulic fracturing by acoustic emission technique.Several parts of work has been done as follows:Firstly,relevant theories of acoustic emission technology and the identification methods of rock failure mechanism based on the acoustic emission technology has been researched.Besides,the advantages/disadvantages and applicability of various methods has been compared.Secondly,type II fracture experiment and Brazil experiment has been carried out in laboratory with monitoring and collecting the acoustic emission signal parameters during the loading process through acoustic emission instrument.Based on the average frequency and RA value judging methods,the rock failure mechanism has been analyzed and the results fit well with the destruction form of samples.Thus the feasibility of the method based on average frequency and RA values is verified.Lastly,large size true triaxial experiment of four shale outcrop has been carried out in laboratory.The experiment data has been analyzed by the average frequency and RA value judging methods.The result shows that natural fracture not only affect the extension of hydraulic fracture,but also cause the change of shale failure mechanism during the process of hydraulic fracturing.When hydraulic fracture diverts and connects natural fractures thus forming complex fracture network,many shear acoustic emission events will occur. |
PDF Full Text Request