ASSESSMENT OF CO_2 CORROSION DAMAGE DISTRIBUTION IN OILWELLS BY DETERMINISTIC AND STOCHASTICAL MODELLING

摘要

In the present paper, an a priori corrosion damage distribution assessment methodology is implemented to study the production casing failures observed in oilwells operating within a mature oilfield (Oritupano A, Venezuela). The methodology developed aims at the assessment of corrosion damage and subsequent probability of failure. The study approach is based on the mechanistic modelling of CO_2 corrosion coupled with a stochastical simulation for the associated corrosion damage distributionThe stochastical model developed for the assessment of the corrosion related damage distribution was based on the simulation of the CO_2 corrosion mechanisms. The results obtained from the evaluation of the model proposed shows that it can quantitatively indicate the transition from uniform damage distribution to localized forms of CO_2 corrosion attack.The modelling methodology proposed was used to calculate the survival probability curves for the production casing, exposed to the produced fluids from the Oritupano A field, in both vertical and deviated wells. The results obtained indicate that the deviated wells can experience a casing failure event every 6 years of service time; in contrast, the vertical wells show a much higher failure time interval. These results were validated with the actual workover information from the field.