Sampling and analysis of sour gas is hazardous and can lead to fatality if appropriate safety precautions are not taken. Similarly if improper technique or instrument is used for measurement, it might lead to high error and the results will be unreliable for process control. The prime objective of this paper is to develop safe sampling and lab analysis procedure and adapt right analytical technique and instruments for accurate measurement of chemical composition of sour natural gas.
Sour gas contains hydrocarbons ranging from C1 up to C9+, carbon dioxide, oxygen, hydrogen sulfide etc. and its composition depends on the source, operating conditions etc. A novel technique of sample collection with strict safety regulations and adequate protective equipment's are implemented to avoid exposure to toxic H2S gas. Right configuration of sampling point connected to flare system with control valves and tools help us to extract a representative sample without any leak into atmosphere. An extended training in handling such toxic gas is provided to the staff performing sample collection and analysis. The conventional method for analysis of sour gas composition is GPA 2261 using gas chromatograph which is inadequate and the gas composition is incorrect due to fractionation or condensation of heavier fractions.
We have changed the configuration of the gas chromatograph adapted a modern technique of sample stabilization using a temperature controlled oven and enable automatic injection of several samples through programmed sequential operation. The results show good repeatability and high sensitivity for heavier fractions and other components. The equipment is calibrated before testing the sample with a primary standard of known composition. The results of both detectors (TCD for inert and permanent gases and FID for hydrocarbons) are combined using i-pentane and n-pentane as bridge compounds and calculated the relative response factors for each component and the gas composition. Applying the novel techniques of designing proper sample points, using right tools and modern instrumentation, we could ensure that the sample is homogenous and representative of the bulk supply in plant. We could completely eliminate exposure to toxic H2S gas by using personnel protective equipments and avoid any leak in to atmosphere by connecting it to flare. Changes in the configuration of gas chromatograph, test conditions and parameters helped us to improve the accuracy and precision of measurement. These simple methods of sampling and analysis of sour feed gases is applicable to all oil and gas industries and sharing these safety guidelines and right approach for accurate analysis will help the operations team. This is an effort towards our commitment to safety of personnel and operational excellence.