A Case Study on Enhancement of Separation Capacity at an Offshore Process Complex

Abstract

In one of the offshore complex of ONGC, Carryover of liquid have been observed leading to tripping of gas compressors resulting a loss of significant amount of production. It was established that separation capacity of existing separators even at present operating conditions were not sufficient to process present production. Further an increase of 60% of present gas production is envisaged as per long term production profile. Hence, handling the present and envisaged increased production in the existing separators was explored. To handle the envisaged enhanced production rate and to avoid carryover issue in existing separators, options such as feed nozzles enhancement and installation of inlet device was explored. Changing feed nozzles is a tedious job, require hot job and longer shut down period and requires complete integrity test of separators as recommended by ASME SEC-VIII, pressure vessel guidelines followed by R-stamping. Therefore modifications in separator internal was suggested which will enhance the separation capacity and can accommodate in the present and envisaged increase of future production. The analysis revealed that even though the diameter and length of the separators are adequate to handle the load, it was established that the inlet nozzle of the separators are not adequate. Hence, considering many factors such as minimum pressure drop, ensuring good gas distribution, suppression of re-entrainment, momentum reduction and erosion velocity ratio of less than one, modifications in separator internal was suggested which will enhance the separation capacity and can accommodate the present and future envisaged increase of production of more than 60%. It was established in the study that this options of installation of inlet device can be done with minimum modifications and require minimum shutdown period. This option has been recommended and is under field implementation. Hence this work will provide a significant help to oil and gas personal to accommodate higher than design feed quantities in existing separators with minimum modifications and minimum shutdown period.