Effects Of Nanoparticle And Inhibitors On Hydrate Formation And Agglomeration And Evaluation Of Drilling Fluid Properties

Natural gas hydrate is an important potential alternative energy for conventional oil and gas.It is not only the focus of academia,government and enterprises,but also the strategic commanding point of global energy development in the future.Well drilling operations are integral to the exploration and development of natural gas hydrate.However,drilling fluid would invade reservoirs under certain conditions,which may lead to borehole instability and well-logging distortion.To eliminate the adverse effects,it is necessary to reduce drilling fluid invasion.Adding nanoparticles is one of the effective methods to improve the anti-filtration,pore or fracture plugging ability of drilling fluid and wellbore stability.In addition,it has been found that a certain concentration of hydrophilic nanoparticles can inhibit hydrate formation.However,the influence mechanism of nanoparticles on hydrate formation is not clear;The influence law and mechanism of nanoparticles on hydrate agglomeration are rarely reported;The effect of the compound of nanoparticles and hydrate inhibitors on the hydrate formation and agglomeration has not been revealed;Besides,the effect of nanoparticles on the performance of drilling fluid is not clear,especially the interaction between hydrate drilling fluid and hydrate reservoir.Therefore,in view of the above research deficiencies and based on our previous work（Effects of hydrophilic and hydrophobic nanoparticles on the macroscopic kinetics of hydrate formation）,this paper further used a variety of experimental methods to reveal the influence mechanism of hydrophilic and hydrophobic nanoparticles on hydrate formation;Besides,the effect of nanoparticles on hydrate formation and agglomeration in oil-water system was studied;The effects of the compound of nanoparticles and hydrate inhibitors on hydrate formation and agglomeration in different systems were also studied;Finally,a new nano-based hydrate drilling fluid was designed and evaluated,and the corresponding reservoir protection scheme was put forward.This study will have important theoretical and application values for the design of deepwater and hydrate drilling fluid system,logging identification and evaluation of hydrate reservoir,hydrate reservoir protection and wellbore stability evaluation,as well as the design and safe operation of multiphase mixed transportation（oil,gas and hydrate slurry）pipelines,and will provide some technical support for safe drilling and efficient production of gas hydrate.The main conclusions are as follows:（1）The influence mechanism of nanoparticles on hydrate formation in water phase.The hydroxyl（-OH）on the surface of nano-CaCO₃ makes the solid particles hydrophilic and the hydrophobicity of nano-CaCO₃ is determined by a certain amount of methyl（-CH₃）and methylene（-CH₂）.Hydrophilic and hydrophobic nanoparticles have certain effects on mass transfer.Hydrophilic nanoparticles slightly increase the diffusion coefficient of CH₄and the solubility of CH₄ in water,but have no obvious effect on the hydrate phase equilibrium conditions.On the contrary,they will increase the CH₄concentration difference between the hydrate-aqueous solution interface and gas-aqueous solution interface,which is conducive to the transportation of CH₄ from the gas phase to the hydrate surface;In addition,hydrophilic and hydrophobic nanoparticles have a significant effect on the state（activity）and the hydrogen bond network structure of H₂O molecules but different in degrees.Therefore,the main reason for the inhibition effect of hydrophilic nanoparticles on hydrate formation is that the hydrophilic surface changes the state of water molecules（from free water to bound water）and destroys hydrogen bond network structure of H₂O.This will affect the intrinsic kinetics of hydrate formation and is not conducive to the hydrate nucleation and growth.（2）The effect of hydrate formation and dissociation on the stability of oil-water interface and the effect of anti-agglomerants（AAs）on hydrate formation.When hydrate nucleates and grows rapidly near the oil-water interface,the interface will be destroyed,which is mainly caused by the concentration gradient of CH₄ and Marangoni effect.When the hydrate is dissociated by heating up,the system reaches equilibrium again and a new stable oil-water interface appears.The CH₄ diffusion behavior induced by chemical potential gradient during hydrate formation and dissociation affects the stability of emulsion.Therefore,a new hydrate induced instability model is proposed for different types of oil-water emulsions.In addition,it is found that AAs can promote hydrate formation in pure water（100%）and high water cut system（95%）.In the system with relatively low water cut（20%and 60%）,AAs will slow down or even completely prevent the hydrate nucleation and growth,which may be mainly due to the steric effect of AAs for mass transfer.（3）The effect of nanoparticles on hydrate formation in oil-water systems.Without the addition of nano-CaCO₃,hydrate is very easy to form and aggregate in oil-water system whether with high or low water cuts,which will have an adverse impact on flow assurance and actual production.When different concentrations of hydrophilic nano-CaCO₃ are added to the oil-water system,hydrate formation is inhibited in most cases,and hydrate formation is completely prevented in some cases（such as40%OW+1.0 wt%）.It is further found that hydrophilic nano-CaCO₃ have a better inhibition effect on hydrate formation at high water cut;Similarly,hydrophobic nano-CaCO₃ particles can also inhibit hydrate formation under some conditions,and the inhibition effect is better when the water cut is low.The concentration has a certain influence on the experimental results,but it shows no obvious regularity.Therefore,we can select suitable nanoparticles according to the actual situation（high and low water cut）to inhibit the hydrate formation and agglomeration.（4）The effect of the compound of nanoparticles and hydrate inhibitors on hydrate formation.PVCap,Na Cl and PKO are selected to further compound with nanoparticles after comparative analysis.Compared with nano-CaCO₃ aqueous solution,the combination of hydrophilic nano-CaCO₃ with thermodynamic inhibitor（THI）and kinetic inhibitor（KHI）inhibits the hydrate nucleation and growth,and the compound with KHI completely prevents the hydrate formation;However,the compound with salt has no synergistic inhibition effect,and the inhibition effect of the compound is not as good as that of Na Cl alone.The compound of nano-CaCO₃ and AA weakens the inhibition effect of nano-CaCO₃ itself,which is antagonistic.In addition,the combinations of hydrophilic and hydrophobic nano-CaCO₃ particles with Span80 in40%oil-water system completely prevent the hydrate formation under the experimental conditions.The addition of Span80 reduces the solubility of CH₄ in the system,which is helpful to prevent hydrate formation and agglomeration.（5）The effect of nanoparticles on hydrate agglomeration.The addition of nanoparticles will change the morphology of THF hydrate.The surface of pure THF hydrate is smoother,while the addition of nanoparticles makes the appearance of aggregates on the hydrate surface,especially for hydrophobic particles.There are many circular aggregates on the sample surface of THF hydrate+hydrophobic CaCO₃.Compared with THF pure hydrate samples,the addition of hydrophilic nanoparticles reduces the adhesion of the samples,while hydrophobic ones increase the adhesion of the samples.The results also show that hydrophilic nano-CaCO₃ is more suitable as an additive for hydrate drilling fluid system than hydrophobic particles.（6）Performance evaluation of new nano-based hydrate drilling fluid.The colloid ratio of the designed nano-based hydrate drilling fluid system is more than 97%;The density is between 1.08-1.10 g/cm³,which satisfies the requirements of safe mud density window for drilling in marine hydrate bearing sediments;The apparent viscosity（36-79.5 m Pa·s）,the plastic viscosity（27-42 m Pa·s）,and the dynamic shear force（8.176-38.325 Pa）are in line with the design values,which show that the drilling fluid has good rheological property.In addition,the concentration of nanoparticles has an obvious effect on rheological property,so the added amount of nanoparticles can be adjusted according to the actual drilling requirements;The p H value is about 7,which can be adjusted by adding alkaline substances.Besides,with increasing the concentration of nanoparticle,the filtration of drilling fluid gradually decreases,which will greatly improve plugging performance of drilling fluid and weaken the invasion of drilling fluid into the reservoir.Therefore,the designed drilling fluid system will be helpful for protecting reservoir,and be suitable for drilling in marine hydrate bearing sediments.