Prediction Of Perforation Erosion During Multi-cluster Hydraulic Fractur-Ing In Horizontal Wells

Unconventional oil and gas resources,such as Shale Gas,Shale Oil,etc.,play an important role in China’s oil and gas production.Largescale hydraulic fracturing technology based on horizontal wells is the key to raise the shale gas and shale oil production.In the fracturing 2.0 process,limited entry perforation technique can significantly increase the fracture opening rate,but temporary plugging and steering process is the important process for the this technology.The temporary plugging ball always cannot be effectively plugged due to the perforation erosion resulting in the failure of the limited flow injection technique.Therefore,it is the key to investigate the erosion pattern of the injection perforation and the temporary plugging mechanism of the eroded perforation.Firstly,the evolution of the erosion process and the decay process of the frictional resistance of the perforation were obtained by using the Discrete Element Method(DEM)and CFD method for a single perforation on a 51/2in × 10.54mm P110 casing.In the hole shoulder erosion stage,the shoulder area of hole is transformed from a sharp edge to a smooth surface,thus making the eyelet friction decay dramatically.In the expansion erosion stage,the expansion of the diameter of the perforation leads to a sharp decrease of the flow velocity of the perforation,which leads to a decrease of the carrying capacity of the fluid to the temporary blocking ball.On this basis,a prediction model of perforation erosion considering the two main influencing factors of sand content and perforation flow velocity is established by experimental method.Secondly,combined with the validation by flow loop experiments,the flow inhomogeneity coefficient and sand discharge inhomogeneity coefficient with erosion time is proposed based on the geometric reconstruction after erosion for the single-cluster with six perforations casing.By using coating modeling and coating erosion experimental method,a multi-perforations erosion rate prediction model is established considering the inhomogeneity of single cluster multiperforations and erosion deviation.The prediction software was developed to predict the erosion expansion of multi perforation pores.The transport behavior of temporary plugging balls in the casing without perforation and the temporary plugging behavior in the single-cluster with six perforation casing were investigated by using the Macroscopic Particle Model(MPM)numerical simulation method combined with the flow-loop test.For 51/2in × 10.54mm casing,the temporary plugging balls can achieve temporary plugging by gravity when the displacement is 4m3/min.It is beneficial to the perforation plugging that increasing the displacement,When the fracture displacement is between 4 m3/min and 10 m3/min.When the fracture displacement is between 14 m3/min and 20 m3/min,increasing the displacement increases the waiting time for the balls,which is not beneficial to the perforation plugging.Changing the ball density and particle size will affect both the transport trajectory and sealing position as well as waiting time.It will help improve the overall sealing effect by choosing 1.3 times of the number of perforations for the number of balls,and two times for the number of segments.Finally,a numerical simulation study of the coupling between the temporary plugging pro cess and the erosion was carried out by using MPM with geometric reconstruction.The results show that the average frictional decay of the perforation is up to 10.30 MPa when the multiperforations is eroded for 1500s later.The transport and plugging behavior of the temporary plugging balls were investigated by reconstructing the computational domain after erosion.The results show that the temporary plugging with balls can effectively plug the dominant injection perforation and cause the casing pressure to increase.The casing pressure increase is 8.7 MPa when three perforations are plugged in a single cluster of six perforations.The perforation friction is restored from 3.67 MPa to 12 MPa,which is close to 13.97 MPa before the erosion.The temporary plugging technology can reduce the probability of failure of limited entry perforation technique.