| Coiled tubing volume fracturing technology is one of the main fracturing technologies for horizontal well development,which can increase the contact area between fractures and reservoirs and raise the oil production of single well with ultra-low permeability reservoir by improving the reservoirs exploitation longitudinally and realizing high strength laterally.At the same time,the technology has the advantages of high rig efficiency,safety health environment,and low cost.According to the current application of the technology in Daqing Oilfield and combined with the composition and characteristics of the technical pipe string,the paper adopts the theoretical and experimental methods to design the structure of key tools,optimize the parameters,and improve the material and performance.The above research work is as follows:When applying the conventional dual-packer multi-stage fracturing technology by pulling up the string stage by stage for the new or old wells,some problems,such as serious tool abrasion,frac string broken accident and heavy lifting workload after fracturing,were tend to happen during the volume fracturing operation with large displacement and large sand loading volume.For K344-110 packer with small diameter,the steel structure,sand filter and pressure-transmitting channel and erosion resistant structure of inner channel were designed and the material was optimized.The shoulder of the rubber packing element vulnerable to failure was designed as circular arc transition structure by using the finite element method,so the stress concentration could be reduced by 14%.The cord angle was optimized to be 15°by adopting the experimental method.The shape of the sand blaster was optimized as porous structure,and pore diameter and pore spacing were calculated by using the computational fluid dynamics method.The structure of the pressure-transmitting channel was improved based on the principle of separate design.The sealing and position limiting structure of hydraulic hold-down button was designed,and the structural parameters,material and carburizing process of the anchor claw were improved as well.So the inner diameter of the hydraulic hold-down button could be increased from?46mm to?60mm.The pressure adjustable mechanism controlled by tubing and casing differential pressure and the double sealing structure composed of central valve plate and torsion spring were designed to solve the problem of tubing blowout prevention.Through the improvement of the key tools and the technology,the coiled tubing dual-packer fracturing technology by pulling up the string stage by stage rated up to differential pressure of 80MPa at 120°C was developed,which has been applied to 546 sections of 62 wells in the field test of Daqing Oilfield.It provides more reliable tools and technology for the new wells with 5 1/2?casing cementing completion or repeated multi-stage fracturing in the old wells.When applying the coiled tubing hydraulic jet and annulus sand fracturing technology for the new wells,there were some problems existed in the packers,such as difficult setting,easy sand-sticking,hard releasing and easy to damage the rubber packing element,etc.A type III sealed single rubber packing element was designed with composite sealing mode and shoulder protection mechanism,which rated up to differential pressure of 80MPa under 20k N setting force at 150°C.The structural parameters and material of the slip were optimized by the finite element method.By using the numerical simulation of the jet flow in the nozzle,the curve radius of the nozzle inlet,the length of the straight line,the diameter of the outlet and the distance between the nozzles were optimized.Both the connection structure of the spray gun outer shell,and the limiting and fixing mode of the gun body and the outer shell were improved.The whole salt furnace quenching process was changed to the local heat treatment process.The structure of single flow valve was designed by the combination of round table metal valve seal and L-type rubber seal.High-conductivity friction adjustable positioner,balance valve,safety release sub,centralizer and other tools were equipped.Through the improvement and equipment of these tools,the coiled tubing volume fracturing string and technology were greatly improved,which has been applied to 972 section of 84 wells in the field with the maximum operation pressure of 69MPa and displacement of 16.5 m3/min.It meets the requirement of high-efficiency volume fracturing for new wells with 5 1/2?casing cementing completion in low-permeability tight reservoirs.The research improves the performance of key tools in the coiled tubing volume fracturing and promotes the progress of the coiled tubing volume fracturing technology in Daqing Oilfield,which provides guidance and reference for the development of other fracturing technologies in China. |
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