Fracture Morphology Evaluation Method Based On Microseismic Interpretation

As one of the effective methods to explain the shape of artificial fracture(fracture length,fracture width,fracture height)and the process of fracture propagation,the accuracy of fracturing fracture interpretation by microseismic monitoring method is affected by whether the monitoring event points are effective or not.Consequently,the hydraulic result evaluation and fracture propagation behavior research will be adversely affected.Aiming at the tight sandstone reservoirs of Qie-6 block,Qinghai oilfield and shale reservoirs in Jiaoshiba,this paper studies the correction method for improving the interpretation accuracy of microseismic monitoring technology combined with the physical simulation of fracture morphology in laboratory.The main work includes the following parts:Considering the difficulty of depicting the hydraulic fractures morphology accurately using microseismic monitoring alone,this paper proposes a fracture communication mode classification method based on the principal component theory analysis and deduces the correction coefficient(fracture length,fracture height and fracture volume)of fracture geometric parameters,which could be used for correcting the fracture parameters interpreted by microseismic commercial software and portraying fracture surface after fracturing accurately.Taking well(section)in Qie-6 and Jiaoshiba as example,the analysis results show that the fracture correction coefficient increases with the increase of fracture complexity in both sandstone and shale reservoirs,and the high efficiency of fracture making in the same category of Qie-6 can be found out and the fracturing parameters can be analyzed to provide guidance for the subsequent optimization of fracture construction.By comparing the characteristics of the physical simulation pump injection curve and the field pressure drop curve of shale gas reservoir,the correlation between the fluctuation response of the field pressure drop curve and the fracture shape is mastered,and the discrimination method of fracture shape interpretation by the fracture curve is established.The results show that the mechanical properties,dimensions and internal discontinuities of the test piece will affect the shape of the indoor fracturing;most of the fractures corresponding to the stable pump pressure curve are artificial fractures with open bedding fractures,and the cross fractures connecting the bedding planes mode corresponding to the pump pressure curve with low start and gradually increase,while the cross fractures corresponds to the pump pressure curve type of high start decreasing gradually,U-shaped and middle pressure lifting;the hydraulic pressure corresponding to the pump pressure curves with low start and gradually increase and stable pump pressure curve The fracture propagation is blocked in the longitudinal direction,which results in pressure holding in the fracture.The above identification method reveals the dynamic response mechanism of fracture propagation.Based on the shortest distance method,the effective points of microseismic are identified and the volume of SRV is calculated by using the improved octree algorithm theory.Taking SRV as the optimization target,the correlation degree between the controllable construction parameters and the post fracturing effect is calculated by using the grey correlation analysis,and the main control factors of the fracturing effect are evaluated,which can provide the basis and guidance for the field fracturing parameter optimization.The result of noise removal of Jiaoshiba shows that the calculation accuracy of SRV can be greatly improved by using the shortest distance method to identify the microseismic event points;For Jiaoshiba,the average sand ratio,fracturing fluid displacement and perforation cluster number are the main control factors affecting the field fracturing results,while the hydraulic fracturing site of Qinghai Oilfield can optimize the type and performance of fracturing fluid by focusing on adjusting the amount of preflush and the average sand ratio,optimizing the type and performance of fracturing fluid to improve hydraulic fractuing effect.