Maximising the Life of Corroding Tubing by Combining Accurate Multi- Finger Caliper Data with Corrosion Modelling

摘要

The purpose of this paper is to discuss the relationship and value brought by empirical field data measurement, extensive interpretation and analysis of that measured field data and powerful predictive modelling with the input of multiple production parameters, for the prediction of rate of corrosion in downhole completions. This paper involves studies conducted upon Tullow Oil’s Bangora Field in Block 9, Bangladesh. Compositional analysis of the gas produced from discovery well Bangora 1 identified CO2 as being present at a concentration of around 0.6 mol%. Initial corrosion modelling highlighted that carbon steel completions were not suitable for long term production in this environment, however carbon steel completions were installed for logistical reasons and a corrosion monitoring programme utilising multi-finger caliper surveys was put in place. These surveys identified extensive corrosion of production tubing within a short period of production. Accurately calibrated multi-finger sensor measurement was performed and repeated four times within a 2 year timeframe by Read Well Services. Intetech Ltd was engaged to carry out detailed corrosion modelling and prediction with input parameters including fluid production rates, well head and bottom hole pressures and temperatures and produced fluids composition. This modelling and direct measurement of the corrosion rates showed a good level of agreement and have given confidence to the life of the completion in relation to the rate of corrosion before expected failure. The technical benefit of this work has been that it has reduced the risk that a tubing leak arises, which would require the well to be shut-in resulting in significant deffered production and associated loss of revenue while waiting mobilization of workover equipment. Cost savings have arisen by being able to safely defer the time to workover of the wells in a location where workover equipment is not readily available and to reduce the frequency of caliper surveys. Tubing replacement is planned at as late a date as possible consistent with the modelling predictions, thus maximising the useful life of the string.