At the final stage of gas field development, the reservoir pressure and the volume of produced gas are decreasing. At the same time, the moisture content of reservoir gas and the amount of produced formation water are increasing. It leads to the appearance of additional operation problems affecting on the stable operation of gas gathering and gas treatment systems. In particular, in the winter season there is primary risk of ice depositing in-field pipelines. In comparison, at the initial stage of field development the hydrate formation in-field pipelines took place. In any cases methanol is used both to ice and hydrate control.
The analysis of the current operation parameters of the complex gas treatment plants (CGTP) of the Cenomanian deposit of the Yamburgskoye field shows that at dehydration units’ methanol vapors in addition to water vapors are extracted from the natural gas. This worsens the performance of CGTP. So, it is necessary to optimize the technological parameters of the absorption process to provide both the dew point specification and amount of extracted methanol vapors.
To achieve the purpose under consideration, a technological model of absorption units is developed taking into account the extraction of methanol vapors from the gas. Model was adapted from the field data (by the analysis of water content in lean and rich diethylene glycol (DEG) as well as in reflux). Based on the results of the simulation the influence of the key parameters on dried gas dew point is estimated.
Recommendations are proposed for adjusting the operating modes of the CGTP, taking into account the maximum possible reduction in operating costs. In particular, a significant reduction of the irrevocable losses of methanol is ensured. The specific rate of the lean DEG fed to the absorber is used as a regulated parameter for the operating mode of the CGTP. The centralization of production facilities takes place at the latest stage of gas field development. So, the possibility of preliminary gas dehydration before transportation to mother CGTP is considered.
A criterion for reducing the operational costs for dehydration process is proposed. It allows to determine the optimal parameters of the operating modes of the absorption and to regulate the water dew point of the dried natural gas at the entrance to the main gas pipeline by changing the dehydrating depth for each of the CGTP. In case of centralization of production facilities, the stage of preliminary gas dehydration reduces the risks of ice deposit in the inter-field pipelines. As a result, the specific consumption of methanol is reduced.