Gas Hydrate Prediction Model And Its Applications

Gas hydrate formation during exploitation and transportation is a well recognized operational hazard. It can impose serious accidents such as the choke's plugging, the gas well's off production. In order to avoid gas hydrate plugging the equipment, general gas hydrate forecast model is needed. Accounting for the environmental fact of gas hydrate formation such as temperature and pressure of gas flow through pipeline and choke, inhibitor and inhibitor's concentration, general gas hydrate forecast model is established, which supplies a more reliable technical support for the technical design of gas hydrate prevention. Based on energy conservation theory and van der Waals's mixed rule, a mathematical model considering phase equilibrium with Peng-Robinson equation is deduced to describe gas flow through choke and temperature drop through choke. A series of data points are acquired from the Brown enthalpy-entropy diagram to calculate by this model. At relative wide range, the results acquired from the model match well with the values from the Brown enthalpy-entropy diagram.Applying the gas hydrate forecast model of Du and Guo, combining their improved Peng-Robinson equation, calculation equation of water's activity coefficient is educed based on the consider of the infection to the system's equilibrium from alcohols and mathematical model is extended to the system containing alcohols. Combining the new gas hydrate thermodynamics model put forward by Zuo and Guo with improved Patel-Teja phase equation from Zuo, the mathematical model is expanded to the system containing salts. The general gas hydrate forecast thermodynamics model has merits such as wide adaptability and good convenience.The software of predicting the temperature and pressure of gas flow through pipeline and choke, the gas hydrate forecast is programmed in Visual Basic language, which supplies technical design means for preventing the gas hydrate formation. Also, for methods preventing gas hydrate from formation such as heating, reducing pressure, dehydration and injecting inhibitor, the gas's maximalallowed water content and the minimum amount of inhibitor injection for avoiding hydrate formation are computed especially.The case calculation is done with field data. The paper makes the predictions which include temperature, pressure, the maximal allowed water content, gas hydrate formation condition of the gas between gas wellhead and jacket heater, and analyzes such influence facts as gas relative density, propane content and water content on the formation of gas hydrate, also makes carefully calculation and analysis to the system containing thermodynamics inhibitor.