Summary Sea lines transporting gas toward the north (Iran) and south (Qatar and Saudi Arabia) and originating from fields located in the central parts of the Persian Gulf exhibit different thermal regimes. The lowest reported arrival temperatures of the gas were 18 and 11°C for the sea lines transporting gas to the northern and southern shores, respectively. The difference between the two is significant and could radically alter the hydrate-mitigation strategy and the associated economics. Metocean data reported in this study and from previous studies (Appendix A) show that the northern part of the Persian Gulf, which is also deeper, attains a well-mixed state during winter months. During this phase, the arrival temperature of the gas for South Pars (SP) sea lines decreases steadily and goes through a minimum at approximately the middle of February every year. In the southern region, the sea is shallow and water is more saline. Sinking of saline water when exposed to cool and dry ambient winter conditions is probably responsible for the reported abrupt decrease in arrival temperatures in the case of the Karan gas line. The immediate recovery of the same may be caused by the local wind/tide conditions. The likely origins of the observed lowest temperatures in the north and south regions are Arctic winds of short duration and desert winds of fairly long duration, respectively. This study summarizes hydrate-inhibition practices for these sea lines, and indicates a possibility of using the sea lines as “indirect thermometers” to provide important physical oceanographic data for long terms in a limited but economical way with fewer interruptions.

The sour gas after H2S removal, sub cooling and dehydration is routed to the dew pointing and mercaptans removal unit that was designed with objective of separating light mercaptans with C3 and C4 and removal of heavier mercaptans with C7 + (lean oil). Blockage in lean oil stream resulted to plant operational problems, such as off spec result in export gas, feed gas reduction and high methanol injection. In this paper hydrate, wax, ice formation and TEG freezing are evaluated by QCM and GC as potential causes for this blockage. Test results appeared that the solids are not heavier hydrocarbons crystallizing. None of the chemical treatments aimed at removing/reducing problems associated with the crystallization of hydrocarbon solids were effective for the solids formed in the fluids tested in this work. It also indicated that the melting point of the solids, ice, as measured by the QCM is related to the solubility of the water in the sample. The effect of TEG must be very small, as the solid formation problem was almost eliminated after drying by calcium chloride. Finally, the preceding findings suggest that ice is the cause of the solids formation at low temperature and methanol injection at a rate of over 400 ppm by mass can prevent the formation of solids.