Study On Sulfate Scale Model Based On Thermodynamics And Kinetics Theory

Injecting water is a very important method for maintaining the formation pressure and enhancing the oil recovery,but it is often accompanied by scaling in the process of water injection.It will produce sulfate scale,blocking the pores of the reservoir and the throat,the serious reservoir damage,when the injected water is mixed with the formation water.This is caused by the change of the thermodynamic conditions or the incompatibility of the SO42-in the injected water with the Ca2+ Ba2+ Sr2+ and other scale cations in the formation water.Therefore,establishing a reasonable mathematical model to accurately predict the scaling of sulfate and evaluating the effect of scaling on infectivity index of water injection wells are very important for ensuring a reasonable water injection plan.Firstly,the scaling mechanism,scaling characteristics,influencing factors and the relationship between the scale and the well productivity were analyzed in this paper.Secondly,the improved Oddo-Tomson thermodynamic model,one-dimensional core node sulfate chemical kinetic model,the one-dimensional prediction model of barium sulfate scale in the near-well area of the injection well and the formation of the two dimensional scale ion distribution model were studied respectively.Finally,the injectivity index of water injection wells and the influence of various factors on injectivity index are predicted.Specific results are as follows:(1)The program of the improved Oddo-Tomson thermodynamic model is compiled with Visual Basic 6.0,the scaling of four injection wells in CQ oilfield is predicted and the results are verified by X-diffraction.(2)The three important parameters,the diffusion coefficient,the reaction rate constant and the formation damage coefficient of one-dimensional core node sulfate chemical kinetic model are calculated by the core transient displacement experiment,then the numerical solution of the model is obtained,the dimensionless Ba2+ concentration distribution,the distribution of barium sulfate scale and the change of core permeability damage rate when displacing to a different pore volume multiple are obtained.(3)The one-dimensional barium sulfate scaling prediction model of water injection well was solved.The change of scaling ion concentration near the injection well and the change of the scale of barium sulfate were simulated.(4)The formation of two dimensional scaling ion distribution model of the point source well is solved and the distribution of SO42-in the formation after a period of water injection is simulated.(5)The influence of dimensionless reaction rate constant,reservoir damage radius,formation damage coefficient and scale ion concentration on injectivity index were studied based on the one-dimensional barium sulfate scaling prediction model.