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The corrosion behaviour and the remaining safe service life of tubing in simulating production well of polymer flooding in Xinjiang oilfield which located in China was investigated using weight loss measurement and surface characterisation. The results showed that as the chloride ion concentration, temperature and H2S content increased, the corrosion rate of N80 steel gradually increased in the hydrolysis of anionic polyacrylamide (HPAM)/H2S/CO2 environment. The tubing of production well met the requirements of oilfield in polymer flooding. The corrosion scales had two layers: the outer O-rich layer and the inner S-rich layer. The chloride ion concentration and temperature affected the location and the thickness of the S-rich layer. The corrosion scales of N80 steel were composed of FeS, FeS2, FeCO3. Polyacrylamide adsorbed on the surface of steel to form a network film blocked the contact between metal and solution and then inhibited the anodic dissolution of metal. [ABSTRACT FROM AUTHOR]

Flexible composite pipes have the advantages of light weight, corrosion resistance, scale resistance, and low cost compared to carbon steel pipes, and have attracted much attention in the application of onshore oil and gas gathering and transportation systems. Understanding the relationship between the pressure-bearing mechanical properties of composite pipes and their structural characteristics is crucial for guiding their process application. To investigate the mechanical behavior of flexible composite pipes under internal pressure loads, discrete and combined finite element models were established to analyze the stress-strain characteristics of flexible composite pipes. The bursting strength was predicted, and the influence of winding angle and number of reinforcement layers on the pressure-bearing capacity of flexible composite pipes was revealed. The applicability of the two models in the analysis of internal pressure resistance of flexible composite pipes was evaluated using whole pipe strain testing and instantaneous hydrostatic burst experiments. The results showed that the reinforcement layer is the main pressure-bearing layer of flexible composite pipes, and the innermost reinforcement layer bears the highest pressure. The pressure-bearing capacity of flexible composite pipes significantly increases when the winding angle is greater than 53°, and the increase in pressure-bearing capacity slows down when the number of reinforcement layers exceeds 3. Under the combination model, the strain and bursting strength of flexible composite pipes were closer to the experimental results. The study clearly defines the stress-strain characteristics of flexible composite pipes under internal pressure load and the impact of process parameters, providing a basis for the optimization design of single well oil transmission pipelines in Xinjiang oilfield. • The burst strength of flexible composite pipes was predicted. • The applicability of the mechanical properties analysis models of flexible composite pipes was evaluated. • The effect of structural parameters on the internal pressure resistance of flexible composite pipes was elucidated. [ABSTRACT FROM AUTHOR]

Major corrosion influence factors in the production well of CO 2 flooding in Xinjiang oilfield were investigated, and corresponding anticorrosion measures (relating to corrosion inhibitors and corrosion-resistant alloys) had been contrasted in order to select a most suitable scheme to solve the tubing corrosion issue. The results showed that the corrosion of N80 steel in liquid phase was mainly affected by temperature, while in gas phase by temperature and CO 2 partial pressure. As to the corrosion of 3Cr steel, in liquid phase, the influencing factors were temperature and chloride concentration, and in gas phase, it was mainly affected by temperature. The safe service life of N80 and P110 steel in liquid phase were less than 8 years, whereas that of 9Cr and 13Cr steel both exceeded 30 years. In gas phase, the safe service life of N80 and P110 steel were 11.65 years and 16.55 years respectively, while that of 3Cr, 9Cr and 13Cr steel were more than 30 years. Suitable for production well in CO 2 flooding, No.6 corrosion inhibitor was selected. The corrosion rate of tubing could be controlled within 0.076 mm/y by adding 1000 ppm corrosion inhibitor. 9Cr steel was recommended to be used as the tubing of new production wells for CO 2 flooding, and, for old wells, the method of continuous filling corrosion inhibitor was recommended to resist corrosion. • Calculation formula of main factors of tubing corrosion was established. • A rapid evaluation and optimization method for corrosion inhibitors was proposed. • An economical selection model of corrosion protection measures (corrosion inhibitor and corrosion-resistant alloy tubing) was established. [ABSTRACT FROM AUTHOR]