Study On Gas Hydrate Formation Mechanism And Precaution In Wellbore Of Deep Water Drilling

When natural gas reservoir is broached, gas hydrate is easy to assemble on throttle fill up line, marine riser, blowout preventer and well head in sea floor etc., which bring great affection to petroleum exploration drilling in deep water. For this reason, study on the generation mechanism of hydrate in annular of deep water drilling pit shaft, and advisable prevention bring important and profound sense to deepwater exploration drilling in future.Basing on the principle of conservation of mass, principle of conservation of momentum, principle of conservation of energy and the theory of thermal conduction study, the paper establishes computational model of annular pressure and temperature distribution in wellbore of drilling process, and solves it. The computational solution indicates that, it should take precautions against the temperature in marine riser too low which can formate gas hydrate, so the insulating layer of marine riser should be well and the circulation delivery volume should be broadened to the full during the circulating drilling term. When stopping circulation, with the increase of close time, the fluid temperature in wellbore will be close to the outside environment temperature inch by inch, and this make the gas hydrate formation possible.Basing on phase equilibrium theory, applying statistics thermodynamics, the paper builds molecular thermodynamics pure model of gas hydrate. By amending the formula of fugacity coefficient, the paper achieves the gas hydrate forecasting model of electrolyte system. Using UNIQUAC model to get activity of water in wealthy aqueous of non-electrolyte inhibitor, then the paper obtains gas hydrate forecasting model of alcohol system.The paper designs experiment scheme of hydrate formation and dissociation in-house, successively proceeds hydrate experiment of pure hydrate system, inorganic salt additive, alcohol additive, organic polymer mud additive and commercial polyalcohol, then obtains hydrate generation and dissociation curve of different additive with different quality percent. The paper gets hydrate prediction phase curves of different additives after the fit and regression to the laboratory findings. By the method of comparing super-cooling degree, the paper judges the effect of inhibitting hydrate generation of different additive, and then provide a drilling fluid composition. On the base of laboratory datum, the paper inducts relative activity K_A, a new model parameter, and proposes a new hydrate prediction means, which is verified feasible by the inorganic salt laboratory findings.The paper draws up forecasting software of gas hydrate formation on the bases of theory and experiment studies. In view of adding inhibitor of different concentration with different concentration and different natural gas component, the software can provide the forecasting calculation of hydrate formation temperature and pressure.Combining with the research mentioned above, according to the formation mechanism of gas hydrate, the paper introduces effectively well control measure of inhibitting gas hydrate through temperature ascension, pressure release and additive. Moreover, in view of some special gas well operation, the paper also introduces the measure of steam exch and throttling step by step to inhibit hydrate.