Author(s)

S. Al Rawahi & J. Al Harthi

Abstract

This study was carried out because of concern about the hydrogen sulphide (H2S) concentration level in one of the oil fields and its impact on the operation and maintenance teams at the sites. The H2S level rose with the level varying across different wells but the HSE impact was not known. The objective of the study was to determine H2S risk classifications for the off-plot and on-plot facilities based on the design for sour service specification and on physical effects modelling. UniSIM Design R390 software was used to provide process modelling under the operating conditions and it was also deployed in the study to find out: Fluid compositions for different water cut and H2S concentrations, the mass flow rate for the multi-phase streams and gas streams (kg/h). The Shell FRED 6.0 model was used to find out the flow rate of the flashed flow in Kg/s. The fraction of the dispersed gas was calculated by dividing the two values of mass flow rate of the multiphase and flashed gas. The flow rate of flashed gas was calculated by multiplying the fraction of the flashed gas by the mass flow rate of the multiphase. Having the composition of the flashed gas from UniSIM model and the calculated flow rate, Shell FRED was used to calculate the H2S dispersion contour. The outcome of the study was a simple monograph to be used by the operation and maintenance team at the site to classify the off-plot facilities. The on-plot facilities were colour coded to determine the H2S risk in the plant. The classifications determined the minimum requirements for personal protection. Keywords: H2S, hydrogen sulphide, classifications.

Keywords

H2S, hydrogen sulphide, classifications.