Casing Wear: Analysis of Field Experience and Current Models
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Accurate casing wear prediction is important for well integrity evaluations.Some advanced well constructions have the casing exposed to reservoir fluidsand these casings are often in chrome material for corrosion resistance. Experiencein the oil industry shows that chrome materials are more prone towear than regular carbon-steel casings.Two main sources have been consulted to understand the nature of the tasks:Leading specialists in the oil industry and research/scientific work performedon casing wear. Investigating the background for existing casing wear models,scientists and specialists have made themselves available to support thework in this report. The tasks were approached by three categories: Laboratorytests, logged casing wear in a well and modeling the wear.Laboratory tests: In the planning phase of Field Y, extensive casing wear testswere performed to develop an understanding of potential wear problems tobe expected under the specific field conditions. In this thesis, the data setfrom these laboratory tests were analyzed for two casing grades - SM125Sand SM13CrS110 - and used as input in a casing wear model to understandthe correlation between theory and actual wear.Logged casing wear: Multiple caliper logs were run in well X at Field Y tomonitor the wear evolution and to calibrate the wear simulations for wellX. These logs have been analyzed in this report to identify the actual wearextent.Modeling wear: Real operational parameters were fed into DrillNET CasingWearto simulate the wear extent in well X, enabling correlation betweenfield and laboratory results.For the chrome casing, the correlation between laboratory and field is poor.Looking into the background of the wear model it was identified that it is notvalid for chrome materials. Analysis of the tests performed in the laboratorysupported this as the chrome steel showed a linear wear trend - indicating alow or no contact pressure threshold.Today, the industry use the casing wear model also for chrome casing, bendingone of the key input parameter in the expression for wear; the wear factor.In this practice, the wear factor often varies greatly because it is sensitiveto the many parameters involved in wear prediction and to differences fromtheory to real conditions.For the carbon steel casing, the correlation between laboratory and field resultsis good. The wear model was developed to correct for the non-linearwear pattern for carbon steel.In the work of analyzing logged wear it was found that the industry often usesthe reported wall loss without considering the insecurity of the measurements.The following issues were found to be the main tasks to improve:? Add insecurity of logged results in final well integrity evaluations.? Establish a standard procedure for wear modeling.? Develop a wear model for chrome materials, based on extensive laboratorywear testing.