Computer simulation of technological parameters and methods for preventing hydrate formation

Abstract

Relevance. Like many deposits of Western and Central Siberia, the Sakhalin Island deposits (the considered Vostochno-Lugovskoe gas field) faced the problem of gas hydrate formation in wellbores, well plumes and equipment integrated into the technological chain. Hydrate formations clog wells, pipelines and gas pipelines, reducing their working cross-section area. This leads to decrease in flow rate or a complete stop of equipment operation. The operation of valves, measuring instruments, separators and fittings is also disrupted. All this leads to significant economic losses and reduces the efficiency of the field development and operation. The fields that are at the late stages of operation are subject to the greatest influence due to the impossibility of ensuring a hydrate-free operation of wells. From the point of view of the development rationality, it is more profitable to prevent the formation of hydrates than to deal with already formed deposits. It is also worth noting the expediency of transferring the location of hydrate deposition from the well to the surface, where it is much easier and more cost-effective to deal with this complication than in the well. This can be achieved by influencing the parameters of the deposit formation, from which it is impossible to influence the gas composition. Shifting the equilibrium conditions for the formation of hydrates by increasing salinity is also inefficient, since the risk of salt deposition and corrosion increases. Thus, it remains possible to regulate thermobaric parameters by changing a well technological mode of operation, thermal insulation or coating the inside of the tubing with materials, as well as downhole electric heaters, which exclude the possibility of deposit formation. Aim. To substantiate the technology for increasing the efficiency of production wells in the conditions of hydrate formation. Objects. Gas wells operating in the conditions of hydrate formation, as well as the relationship and dependence of the operating parameters of the well and other technological parameters on the potential for the formation of hydrates. Methods. Analysis of the geological and physical conditions and the state of development of the Vostochno-Lugovskoe gas field; computer and mathematical modeling of well operation in the field under conditions of hydrate formation; analysis of ways to prevent the formation of hydrates and the choice of technological solutions. Results. The problem of hydrate formation is widespread in gas fields. Hydrates can partially or completely block the working section of production wells, reducing or completely stopping production. As a result production wells are idle for an average of 18 hours per month. This entails economic losses and interferes with the stable operation of the well. It is shown that due to the specifics of the operation of wells of the Vostochno-Lugovskoe gas field, changing the technological regime to hydrate-free at the moment is impossible. According to the results of well operation simulation, the main temperature losses occur due to heat removal through the tubing. Among the ways to prevent the formation of hydrates, thermal insulation of tubing, partial silicate-enamel coating, the use of a heating cable and methanol are considered. Based on the results of the evaluation of economic and technological efficiency, a heating cable technology was selected with the installation of a turbo-expander to compensate the cost of electricity, as well as the descent of the second row of tubing to the depth of the potential place of hydrate formation in order to increase the heating efficiency and injection coolant or inhibitor directly into the hydrate formation interval.