Study On The Mechanism Simulation And Synthesis Of Swelled-Clay-Shrinking Agent

At present,the high argillaceous oil reservoir of Shengli Oilfield has abundant reserves but is facing the status quo of low mining efficiency and frequent borehole wall instability.The general shale stabilization methods are not efficient enough and the action time is short,which seriously affects the development of the domestic petroleum industry.In order to solve this problem,the paper first analyzes the mechanism of montmorillonite crystal swelling by water absorption from the molecular point of view,and proposes two swelled-clay-shrinking ideas based on the current theoretical research:first,the combination of ion exchange mechanism and multi-point adsorption mechanism;second,the cohesive force of acrylic materials is used to narrow the distance between the crystal layers,and the correctness of the ideas is verified in simulations and experiments respectively.For the clay minerals in shale,we choose montmorillonite crystals as the research object,obtain the relevant unit cell parameters from the inorganic crystallography database,and construct and expand the super unit cell as the basic unit of simulation research.Firstly,water molecules are gradually added to the unit cell for molecular dynamics simulation to simulate the changes in the properties of clay minerals under different degrees of hydration.The simulation data shows that as the hydration stratification deepens,a total of three hydration layers are formed in the montmorillonite crystal,the mechanical properties of the entire crystal structure are weakened,and the free volume decreases.And at any degree of hydration,water molecules are uniformly dispersed around Na⁺,which proves that the hydration cations can adsorb water molecules,and the binding energy of the second hydration layer is weak.According to the conceived shrinkage and expansion mechanism,eight common cations were added to the hydrated montmorillonite crystals for molecular dynamics simulation,and it was found that the hydration ability NH₄⁺<Al³⁺=Ca²⁺<K⁺<Cu²⁺<Mg²⁺<Fe³⁺<Li⁺.In the experiment,NH₄⁺was selected as the replacement cation,N,N-dimethyl dodecyl tertiary amine,1,3-dichloroethane were selected,and ethanol was used as a solvent to synthesize bimolecular quaternary ammonium salt,and then N,N-dimethyl Dodecyl tertiary amine,epichlorohydrin,using azobisisobutyronitrile as initiator to synthesize long-chain quaternary ammonium salt,n（1,3-dibromopropane）:n（epichloropropane）=5:1.When the mass fraction of initiator azobisisobutyronitrile is 0.15%,the mass fraction of solvent is 40%,the reaction temperature is 80℃,and the product mass fraction is 2%,the shrinkage expansion rate is 26.89%.The clay particles treated with quaternary ammonium salt cations were photographed under an optical microscope at 100 times.It was found that the shrinkage agent can make the particles dispersed in the water agglomerate into agglomerates.The contact angle test also showed the contact of the clay particles treated with the shrinkage agent.The angle is greater than 90°,which further verifies the good performance of the shrink-expansion agent.For the second idea,we first simulate the diffusion properties of acrylic acid molecules,and build a polymerization script of acrylic acid molecules,and complete the molecular dynamics simulation of the polymerization of acrylic acid molecules in montmorillonite crystals.The change of the interlayer spacing data indicates that this method can play a certain role in theoretical calculations.The decrease of free volume and the decrease of the abscissa of the peak value of the radial distribution function all indicate that the tensile force of the polymerization reaction can compress the crystal volume.The molecular dynamics simulation of the polymerization of different numbers of acrylic acid molecules in montmorillonite shows that the higher the number,the expansion of montmorillonite will be accelerated.Because the number of molecules has a significant impact on the shrinkage and expansion effect,the experiment started from a low concentration,the acrylic acid concentration was 3%,and the shrinkage and expansion rate reached 16.33%.