Study On Anti-Gas-Hydrate-Decomposition Water Based Drilling Fluid

Gas hydrate is an important alternative energy,improve the drilling efficiency of gas hydrate formation is the basic premise of industrialization exploitation of gas hydrate.Natural gas hydrate exists in deep water and permafrost regions.The natural environment of drilling natural gas hydrate is bad,coupled with the existence of hydrates,which greatly increases the difficulty of drilling technology.The decomposition of natural gas hydrate in hydrate formation(or phase transformation)is very likely to cause serious accidents such as borehole instability during drilling.In view of the problem of wellbore stability in the drilling process of natural hydrate formation,this paper holds that the influence of hydrate decomposition on the stability of the wellbore should be paid full attention to in addition to the traditional hydration and expansion of shale shales.On the one hand,it is necessary to prevent the formation of gas hydrate in the wellbore.On the other hand,we should seek a way to slow down the hydrate decomposition from the chemical means.In order to achieve safe and rapid drilling under the condition of stabilizing hydrate,it is more convenient and economical.The adsorption characteristics of Lecithin molecules on the surface of natural gas hydrate crystals and the decomposition characteristics of natural hydrates are studied by molecular dynamics simulation.The results show that the Lecithin molecules are adsorbed on the surface of gas hydrate,and the choline group and the phosphoric acid group will connect with other adjacent Lecithin molecules in the form of hydrogen bonds.The distortion of the Lecithin molecules may form a network structure,and the decomposition rate of natural gas hydrate will be lower than that of direct contact with liquid water.The rate of decomposition at the time.The adsorption layer formed by Lecithin will restrict the dissolved water molecules and methane molecules on the surface of the hydrate crystal,which can lead to the memory effect of gas hydrate more easily,and further reduce the rate of hydrate decomposition.The inhibition effect of several common chain bisexual molecules is simulated.The results show that the non polar chain length of the molecules,the number of carbon chains connected by polar end connections and the strong or weak intermolecular interaction are the key factors to influence the inhibition effect of the hydrate decomposition.Lecithin>two(twelve acyl)phospholipid ethanolamine>eighteen alkanic acid>twelve alkanoate>water.Among them,the adsorption of Lecithin and two(twelve acyl)phosphatidyl ethanolamine molecules on the surface of the hydrate can lead to the"memory effect of hydrate",which effectively inhibits the decomposition of hydrates.The natural gas hydrate decomposition process at the well wall under the condition of drilling fluid scouring is simulated with the natural gas hydrate comprehensive experimental system.The results show that the inhibition time of hydrate decomposition in Lecithin solution can reach 520min,the best effect and the best use concentration are 0.5%.Three acetate is the best complex of several inhibitors,and the recommended concentration is 0.1%;0.5%Lecithin+0.1%three acetate,in artificial seawater with a salinity of 3.5%,the inhibition time of hydrate decomposition can be up to 598min.Combined with the above research results,the water based drilling fluid system of natural gas hydrate decomposition inhibition type was obtained.The pressure drop of the reaction kettle of 20MPa,4 and 1200min was 1.19MPa,the inhibition time of hydrate decomposition was 297min,and the two kinds of hydrate related properties were greatly improved.The formulation of the drilling fluid is as follows:3%Sea water slurry+0.2%Na₂CO₃+0.2%Na OH+0.2%HEC+0.1%XC+0.3%Largeamine+1%YZFS+1.0%FLO+1.5%TEX+1%LUBE+20%Na Cl+0.5%Lecithin+0.1%Triacetin+0.2%PVP+Barite...