Cavitation-abrasion Behavior And Damage Mechanisms Of Typical Materials In Hydrajet Fracturing

Hydraulic fracturing technology is an effective measure to improve the low permeability reservoir and enhance oil recovery. The high-pressure and high-emission of the multiphase fracturing fluid can lead to a serious cavitation-abrasion damage of the fracturing facilities and casing steels in the process of fracturing operation. This can restrict the construction of safety fracturing operation, and also may be the key to the safe production problem for the oilfield.This paper investigated the cavitation-abrasion damage types and damaged parts features based on the actual fracturing conditions. The erosion and cavitation erosion were simulated by means of solid-liquid and gas-liquid two phase flow model. The erosion and cavitation erosion characterics outside surface of the bybass crossover sub and inside surface of the casing were obtained. The corrosion, erosion-corrosion and cavitation-erosion can be determined as the main damage during the fracturing process.The corrosion rules of the casing steels, bushing hard metals and AC-HVAF protective coatings were studied by means of electrochemical testing methods, and the stability of the passive film was also investigated. The corrosion behavior of materials is directly to the composition and structure of the passive film. The pitting and uniform corrosion resistance of P110 casing steel is higher than those of N80 and J55 casing steels. The uniform corrosion resistance of YG8 bushing hard metal is higher than that of YW2. The amorphous coating exhibits a more stable passivation behavior for the high content of Cr, Mo, Mn and low defect concentration in the passive film, which the pitting resistance higher than that of WC coating.The cavitation-eroison rulus of the casing steels, bushing hard metals and AC-HVAF protective coatings were studied by means of the ultrasonic cavitation and electrochemical testing methods. The leading role of the corrosion resistance and hardness during the cavitation was determined. The corrosion resistance is the first criteria of cavitation-erosion for the casing steels, and the P110 steel shows a better cavitation-erosion resistance. The cavitation-erosion resistance of hard metals and coatings is mainly dependant to the hardness, and the high hardness of the YW2 hard metal and WC coating exhibit excellent cavitation-erosion resistance. The different cavitation-erosion mechanisms were developed. The cavitation-erosion damage of casing steel originates from the ferrite phase and its boundaries, eventually extended to the pearlite phase. The bubbles collapse and impact the pores and defect areas, the hard phases strip off the surface and thus lead to the damage of the hard metals and coatings.The eroison-corrosion rulus of the casing steels, bushing hard metals and AC-HVAF protective coatings were studied by means of the jet impingement and electrochemical testing methods. The erosion-corrosion process was controlled by the mechanical damage resulting from erosion, which the high hardness of the casing N80, YW2 hard metals and WC coating exhibit enhanced erosion-corrosion resistance. The stability of the passive film exerts a certain role in restraining the erosion-corrosion when its velocity lower than the critical velocity. The interactions of erosion and corrosion were determined, and the dominant role of casing steel is the damage caused by mechanical factors. The damage caused by corrosion factors forms a large proportion of the hard metals and coatings. The different cavitation-erosion mechanisms were developed. The casing steel shows a typical ductility ploughing erosion tunnels, and eroded by a layered thinning way. The hard metal and coating exhibit a brittle erosion process, and mainly reflects in the crash and cutting erosion of the hard particles. The decreasing of porosity and increasing of the combining bonding strength is the key to increase the erosion-corrosion resistance of the AC-HVAF coatings.The basis for the materials selection serviced in the fracturing process was proposed. This paper can provide the theoretical basis for material screening and protective coatings during the hydrajet fracturing process, and also give technical guarantee for the safe service of fracturing tools and fracturing operation.