分子模拟无机盐抑制蒙脱石水化机理  

Molecular simulation for inorganic salts inhibition mechanism on montmorillonite hydration

作　　者：徐加放 孙泽宁 刘洪军 付显威[2] 孙中富 李小迪 

机构地区：[1]中国石油大学石油工程学院,山东青岛266580 [2]中国石油化工股份有限公司胜利油田分公司石油开发中心,山东东营257060

出　　处：《石油学报》2014年第2期377-384,共8页Acta Petrolei Sinica

基　　金：国家自然科学基金项目(No.41072094);山东省自然科学基金项目(ZR2012EEM020);教育部创新团队项目(IRT1086)资助

摘　　要：井壁不稳定是油气勘探开发过程中最为复杂的技术难题之一,而井壁的稳定性在很大程度上取决于岩石中黏土矿物的含量特性,尤其是蒙脱石的水化膨胀特性。为深入了解无机盐稳定井壁的微观作用机理,利用分子模拟软件Material Studio(MS)建立Na-蒙脱石的晶体模型,并对其水化过程、水化机理以及水化造成的强度参数变化进行了动力学模拟研究。模拟结果表明,Na-蒙脱:晶体层间距随晶体表面吸附水分子个数的增多而逐级增大,当水分子数达到48、72、96时,分别形成1、2、3层饱和水合层;加入无机后,蒙脱石晶体的力学参数有一定程度的提高;KCl和CaCl_2具有较其他无机盐更好的提高Na一蒙脱石晶体弹性模量、减小膨胀的果。通过KCl、NaCl和CaCl_23种无机盐在不同质量分数条件下对Na-蒙脱石晶体弹性力学性质影响的研究,给出了Na-蒙脱石晶体到最佳稳定状态性时3种无机盐的质量分数范围。膨胀实验结果很好地证明了蒙脱石具有一定盐敏特性,在高质量分数无机盐条下,膨胀率反而增加。该结果对于强水敏性地层防塌机理研究和抑制性钻井液体系的研究开发具有重要的理论指导意义。Instable borehole wall is one of the most complex technical problems for oil and gas exploration and development. The stability of borehole walls depends on the composition and properties of clay minerals in rocks, particularly the hydration expansion characteristics of montmorillonite. For the sake of thorough understanding the micro effect mechanism for inorganic salts to stabilize borehole wall, a Na-montmorillonite crystal model is established using the molecular simulation software Material Studio （MS）, then the hydration process, hydration mechanism and the resulting strength parameter changes are studied by molecular dynamic simulation. Results show that： （1） The spacing of layers of Na-montmorillonite crystal is gradually increased with a growing number of water molecules adsorbed on crystal surface, and the first, second and third saturated hydration layers are formed when the number of absorbed water molecules reaches 48, 72 and 96 respectively; （2） Mechanical parameters of Na-montmorillonite crystal are optimized to a degree after adding inorganic salts; and （3） Compared with other inorganic salts, KCl and CaCl2 have better performances in improving and reducing the elastic modulus and expansion of Na-montmorillonite crystal respectively. Through studying the effect of KCl, NaCl and CaCl2 solutions under different concentrations on the elastic mechanical properties of Na-montmorillonite crystal, their optimum concentration ranges in which Na-montmorillonite crystal has the best stable condition are obtained. The swelling experiment results demonstrate that montmorillonite has a degree of salt sensitivity; when it is put in highly concentrated inorganic salts solutions, its expansion rate will increase. Therefore, this result provides a theoretical guidance for the research of anti-sloughing mechanism of the strong water-sensitive formation as well as the research and development of inhibitive drilling fluid system.

关 键 词：井壁 蒙脱石 分子动力学模拟 弹性模量 无机盐 膨胀 

分 类 号：TE256[石油与天然气工程—油气井工程]