Study On The Technology Of The Prevention And Control Of Hydrates In Deepwater Drilling Fluid

Deepwater oil and gas exploration and development are faced with many complicated technical problems,among which natural gas hydrate is a common problem in deepwater drilling fluid.The formation of gas hydrate will block up the upper annulus,BOP and pipelines,etc.,and limit the drill string activity,resulting in the decline of drilling fluid performance or the occurrence of serious well control accidents.Therefore,it is urgent to explore the mechanism of hydrate formation and inhibition in deepwater drilling fluid,and establish effective prevention and control methods,and optimize the formulation of deepwater drilling fluid system with better hydrate inhibition to meet the drilling development needs of deepwater oil and gas resources.Based on laboratory experiments,the formation and decomposition of methane hydrate in different inhibitors were studied respectively,and the decomposition process of methane hydrate in deepwater drilling fluid was studied by ultrasonic testing technology.First,the hydrate formation experimental facility was used to simulate the dynamic environment of deepwater drilling.The formation rule of methane hydrate in the presence of commonly used hydrate inhibitors in deep water drilling fluid was obtained through experiments.The experimental results showed that the thermodynamic inhibitor could inhibit the formation of hydrates by changing the thermodynamic equilibrium conditions between the water and the methane molecules,and the inhibition effect was obvious.The mechanism of kinetic inhibitors was complex,and its inhibitory effect was far less than that of thermodynamic inhibitors,but it could extend the induction time of nucleation or change the process of crystal aggregation.And with the increase of the amount of kinetic inhibitor,the inhibition effect was more obvious.Secondly,the depressurization process of methane hydrate in three typical inorganic salts?sodium chloride,potassium chloride and calcium chloride?was studied.The results showed that,the reduction of pressure and the injection of inorganic salts could effectively promote the dissociation of methane hydrate.The greater the depressurization,the stronger the driving force of methane hydrate dissociation and the faster the dissociation rate of methane hydrate.The greater the mass concentration of the inorganic salt solution on the whole,the faster the dissociation rate of methane hydrate.This rule was particularly obvious at low pressure lowering amplitude,but when the amplitude of depressurization was large,pressure became the main factor affecting the dissociation of methane hydrate.In the range of the mass concentration of the inorganic salt solution in the range of 5%³0%,the size of the three kinds of inorganic salts to promote the dissociation ability of methane hydrate was NaCl>KCl>CaCl₂.And with the increase of mass concentration,the advantage of NaCl on the dissociation of methane hydrate gradually decreased,and the dissociation rate of methane hydrate in three kinds of inorganic salt solution was gradually consistent.Based on the Kim-Bishnoi model,combining the experimental data of methane hydrate dissociation in NaCl solution,derived a model with three parameters A,B and C of methane hydrate dissociation,and calculated the parameters of the model in different concentrations of NaCl solution.When drilling fluid is used to remove hydrate blockage in the field of deep water drilling,the model is of guiding significance to the selection of NaCl.Finally,the decomposition process of methane hydrate in deep water drilling fluid was studied by ultrasonic testing technology.The results showed that adding hydrate inhibitor in drilling fluid promoted the decomposition of hydrate.With the increase of inhibitor dosage,the experimental time and hydrate dissociation speed increased,and the drilling fluid system suitable for deepwater drilling was selected.The prevention and control of hydrates in deepwater drilling fluid have been realized.