INTRODUCTION
Integrity assessment in ageing exploration and production infrastructure like gathering and flow lines is fast becoming an area of concern owing to the gas fields producing beyond their designed life. The progressive reduction in production flow rate with time magnifies the internal corrosion problems due to bacterial activity and under deposit attack seriously impacts the pipeline integrity. Thus the challenge in integrity management of gathering and flow lines is to accurately predict the internal corrosion rate, detect, size and locate areas of potential internal corrosion and pitting and carry out fitness for service to help enable adequate remediation for safe operation thereby helping to maximize the life cycle performance.
This paper demonstrates a comprehensive methodology for integrity management of ageing gas production lines. The methods involve integration of internal corrosion predictions with intelligent pig data and fitness for service assessment. The remediation strategies are devised based on safety considerations and business needs and they involve a combination of corrosion inhibition, strategic repairs and line maintenance. The method is demonstrated through a case study on a 30 year old 16 Gas gathering line, where strategic repair/remediation allowed continued operation of the asset without curtailing production.
Integrity management of mature and ageing exploration and production pipeline infrastructure is fast becoming an area of concern. E & P (Exploration and Production) systems, especially the pipeline?s pose unique challenges from an integrity standpoint. The pipeline infrastructure is designed to serve the production system, which has a definite and finite life cycle. This life cycle is in the 20-30 year range. As a result, asset integrity programs for E&P pipelines have not been as robust as those in place for the long run transmission pipeline infrastructure. In comparison, it is not uncommon to find transmission pipelines that are in service for over 50 years, whereas E&P lines are 20 or 30 years old.
However, the present operating and business environment has pushed asset integrity of ageing pipelines into the forefront, due to a variety of reasons.
Quite a few E&P pipelines currently are operating beyond their design life cycle. This is primarily driven by newer wells that come on line in existing fields and the prevailing business climate. This phenomenon carries with it various challenges. Pipelines are designed for the initial rate of product, and as the production rate decreases with time, low flow conditions are set up, and these in turn accelerate the corrosion potential in the line. Fluctuations in operating conditions (flow rate, CO2 %, temperature, pressure) and limited understanding in the past of CO2 corrosion and MIC (microbial induced corrosion). mechanism have added to the observed corrosion. Also, owing to the finite life cycle assumed at start of production, many of these lines do not have provisions for internal corrosion inspection or internal cleaning-i.e. absence of pig launchers and receivers, short radius bends etc. Even in lines with such provisions, internal inspection using intelligent pigs, and cleaning are not carried out at the desired frequencies.
E&P pipelines systems have some form of corrosion monitoring (probes, water and stream analysis) and control (inhibitor program). The efficacy of such programs is sometimes questionable due to the lack of internal cleanliness and thus inhibitor availability. This is compounded by intermittent inhibition treatment (due to cost reduction and machine reliability) or in some cases, not enough corrosion monitoring in place (due to the la
