水驱油藏乳液中盐水对沥青质沉淀的影响

Effect of Brine on Asphaltene Precipitation in Emulsions of Water Flooding Reservoirs

油藏注水开发中极易形成油包水乳液,而盐水对乳液中沥青质沉淀的影响机理尚不明确。针对上述问题,在自制实验用油及油包水乳液的基础上,采用分光光度法和油水共注法,分别开展了静态离心实验和动态驱替实验,研究了乳液中含水量、盐类型及盐质量浓度对沥青质沉淀的影响,揭示了盐水作用下沥青质沉淀机理。研究表明:当乳液中含水量由10%增至50%时,沥青质的不稳定性增加,沉淀质量分数由4.5%增至10.6%,但沉淀强度却在减弱。低芳香度的沥青质更容易在水-油界面处沉淀,主要是被界面处水分子表面的杂原子吸附而沉淀。沥青质沉淀量随盐质量浓度的增加呈先增大后降低趋势,当盐质量浓度达到40 000 mg/L时,沥青质沉淀量达到最大。MgCl2、CaCl2、NaCl和KCl对沥青质沉淀量的影响程度依次减弱。驱替过程中40.0%质量分数蒸馏水的乳液的渗透率下降幅度最大,其次为20.0%质量分数MgCl2乳液,而20.0%蒸馏水和20.0%NaCl乳液的渗透率下降幅度最小。动态驱替中盐水对沥青质沉淀的影响小于静态实验,但含水量的增加会增大沥青质沉淀,降低岩心渗透率。研究成果对提高沥青质油藏注水开发效果有重要意义。

Water-in-oil emulsions are very easy to form in reservoir water injection development,and the mechanism of the effect of brine on asphaltene precipitation in emulsions is not clear.To address the above problems,based on the self-made experimental oil and water-in-oil emulsions,static centrifugal experiments and dynamic displacement experiments were carried out by spectrophotometry and simultaneous oil-water injection method,respectively,to study the effects of water cut,salt type,and salt mass concentration on asphaltene precipitation in emulsions,and reveal the mechanism of asphaltene precipitation under the action of salt water.Research shows that when the water cut in emulsion increases from 10%to 50%,the asphaltene instability increases and the mass fraction of precipitation increases from 4.5%to 10.6%,but the precipitation intensity weakens.Asphaltenes with low aromaticity are more likely to precipitate at the water/oil interfaces mainly because of adsorption by heteroatoms on the water surfaces at the interface.Asphaltene precipitation tends to increase and decrease with the increase of salt mass concentration,reaching the maximum when the salt mass concentration reaches 40000 mg/L.MgCl 2,CaCl 2,NaCl,and KCl affect the amount of asphaltene precipitation from high to low.The emulsion with a 40%volumetric concentration of distilled water shows the most significant decrease in permeability during the flooding,followed by a 20%mass concentration of MgCl 2 emulsion,while the 20%distilled water and 20%NaCl emulsions show the smallest decrease in permeability.The effect of brine on asphaltene precipitation in the dynamic displacement is smaller than that in the static experiment.Still,the increase in water cut increases asphaltene precipitation and decreases core permeability.The research results are significant in improving the development effect of water injection in asphaltene reservoirs.