The Internal Corrosion Rule Research And Application Of Shale Gas Well Casings

The casing has a certain value useful and construction costs in the process of oil and gas development.The damaged casing will have a serious impact on the normal production of oil and gas fields.However,the casing corrosion is the most important factor.Therefore,it is necessary to study the casing corrosion of oil and gas wells.In this paper,the main research is the casing corrosion of shale gas well at the exploitation of shale gas exploitation area in the southwest of China.The main analysis is the casing CO₂ simulation and application of corrosion law.The main contents of the study include: the use of field hanging test study on the mechanism of casing corrosion in production wells under the environment;combination of theoretical analysis and indoor hanging experiment study the rule of CO₂ corrosion of casing steel under different influence factors;the CO₂ corrosion rate prediction model is established which can be used in the casing of the shale gas field by using the combination method of corrosion rate prediction model and indoor experiment.The main contents of this paper include:?1?In order to provide the basis for the design and implementation of the experiment,analyzed the shale gas composition,the produced water,the well depth structure,the casing material,the pressure and the temperature of the casing production well in the Jiao Shi dam area.Analysis shows that: shale gas components have different contents of CO₂ and does not contain H2 S or other toxic and harmful gases.The CO₂ is one of the important factors leading to casing corrosion.The ions?Ca2+,Mg2+,Cl-,HCO3-,SO42-?in the produced water can influence the corrosion of the casing.?2?In this part,designed a reasonable and feasible experiment of hanging film corrosion to study on corrosion mechanism of gas well casing.The experiment of hanging film corrosion was carried out to study the 1HF,5-1HF and 5-2HF wells in the Jiao Shi dam area.Experimental results show that: the average corrosion rate of 1HF,5-1HF,5-2HF.The mechanism of casing corrosion in the gas field is mainly the result of the combined effect of CO₂ and salt ions in produced water analyzed by SEM and EDS.?3?The influence of different factors on the corrosion rate of CO₂ was studied in laboratory combined with the engineering practice.Indoor hanging film corrosion test analysis the main factors of temperature,CO₂ partial pressure,flow rate,Cl-concentration,HCO3-concentration and other factors of CO₂ corrosion.Experimental results show that: the main factors affecting the dynamic CO₂ corrosion rate.?4?The prediction model of CO₂ corrosion rate was established on the basis of theoretical analysis and experimental study.The prediction model of the effect of flow rate and Cl-concentration on the corrosion rate of CO₂ was established on the basis of laboratory experiments.The corrosion rate of casing in different well depth was simulated by indoor hanging corrosion experiment.Based on the DWM corrosion rate prediction model,the DWM model was modified by indoor experiment data.The CO₂ corrosion rate prediction model is obtained by using the experimental data in the field.