Research And Application Of Multistage Fracturing Technology In Full-bore Immobile String

The efficient exploitation of unconventional oil and gas resources has become the principal part of increasing oil and gas production in various countries.And one of the core technologies that support the recovery of these particular reservoirs is hydraulic fracturing.The multiple fracturing technology of immobile string was widely used in oil fields at home and abroad,and it generally adopts the sliding sleeve with progressively reduced diameter.This technique makes it difficult to meet the requirements of multi-stage,high-flow fracturing wells due to the limited fracturing stages and displacement.Therefore,through the research and development of full-bore sliding sleeve tools,as well as related supporting tools and technology research,this paper forms a new multistage fracturing technology in full-bore immobile string,to achieve the improvement of fracturing stage and displacement.The design concept of"circumferential grading"was put forward,and a falcon-groove sliding sleeve tool with full-bore was developed.Based on the computational fluid dynamics method,the influence of the working state and the complex boundary of the inner wall of the sliding sleeve was considered,and the numerical model of the fluid domain inside the sliding sleeve of the falcon groove was established.The erosion effect of the sand-containing fluid inside the sliding sleeve of the falcon groove on the inner wall was analyzed.By reducing the eddy field,the structural parameters of the falco groove sliding sleeve were optimized,the erosion resistance of the falco groove sliding sleeve tool was enhanced,and the sand flow rate of the multistage fracturing string was increased.Through the numerical simulation study of the special flow channel structure such as the umbrella key position on nozzle seat,the sand jet closing and opening position,and the position of the sand jet without sliding sleeve,the calculation formula of pressure loss of the fracturing fluid with sand is obtained,which is suitable for the special flow channel structure.So that the hydraulic calculation of full-bore multistage fracturing immobile string is convenient for engineering application.Through the hydraulic calculation of typical immobile string structure and process parameters,when sand ratio is 0-35 and the construction flow rate is 4-8 m~3/min,the pressure loss of the string in vertical,bending and horizontal sections above the clamping distance,the pressure loss of the string in the clamping distance,the hydraulic anchor pressure loss,the pressure loss of K344-116HD packer,the pressure loss of the bridge sandblasting packer in the closed and open state and the pressure loss without sliding sleeve were obtained.It provides the method and basis for hydraulic calculation of fracturing string.According to the structural characteristics and load characteristics of the full-bore multistage immobile string and packer,the rubber tube,the rubber tube seat,the central pipe,the tubing and the casing were selected as the research object,and the dynamic model of the string and packer in the clamping distance was established.The convergence criterion of sliding contact boundary was given.Based on the condition establishment of rubber tube substrate strength,bond strength of fiber interface,pressure seal and string of axial moving,a safety evaluation method for packer seating and sealing was proposed.Through the dynamic calculation and analysis of string and packer in 10-90m clamping distance under different pressure and fluctuation conditions,the variation rules of the contact stress of the rubber tube,shear stress of the substrate,shear stress of the fiber interface and axial displacement were obtained,and the packer seating and sealing security is the highest when the packer was 30m clamping distance,which provides the calculation method and theoretical basis for failure and control of the packer in multistage fracturing.The developed multistage fracturing technology in full-bore immobile string adopts the same outer diameter falcon-wing switch at the wellhead,which can realize multistage stratification reconstruction.Through field experiments in Gao 182-151 well and Gao127-Geng 44 well,the reliability of falcon-groove sliding sleeve,the calculation method of pressure loss and the safety evaluation method of seating and sealing security were verified.And a total of 386 Wells have been used in Daqing oilfield.It can meet the requirements of fracturing technology of vertical well fracture network with construction displacement of8.5m~3/min and a seating and sealing of more than 8 layers,and provides a new technology for multistage fracturing with the full-bore immobile string.