钾离子稳定井壁作用机理研究

Mechanism study on the potassium ion stabilizing wellbore.

研究了钙蒙脱土、钠蒙脱土和钾蒙脱土在清水和7%KCl溶液中的水化膨胀,用X射线衍射仪测定了3种蒙脱土在清水和7%KCl溶液中浸泡后的层间距,结合粘土膨胀机理的最新研究结果,对K+抑制粘土水化膨胀的作用机理进行了探讨。在粘土膨胀实验中发现,KCl溶液在岩心中的渗透速度较清水快,使得在实验前期,岩心在7%KCl溶液中的膨胀高度大于在清水中的膨胀高度,这种现象对井壁稳定是不利的,有必要进行更深入的研究。研究结果表明,在粘土的晶层膨胀阶段,层间阳离子受束缚而不能进行离子交换,因此K+不能有效抑制钠蒙脱土和钙蒙脱土的晶层膨胀;在粘土的渗透膨胀阶段以及完全分散的粘土中,层间阳离子能进行离子交换,K+能有效抑制粘土的渗透膨胀和分散,控制地层造浆。与渗透膨胀相比,粘土的晶层膨胀量低但膨胀压力大,晶层膨胀引起的近井壁地层应力变化对井壁稳定有重要影响。

In this paper,the hydration swelling properties of Calcium montmorillonite,Sodium montmorillonite and Potassium montmorillonite presented in fresh water and 7%KCl solution were studied.The interlayer spacing of each montmorillonite exposed to water and 7%KCl solution were measured respectively with X-ray diffractometer.On the basis of update research findings on clay swelling mechanism,clay stability mechanism of potassium ion was discussed. It was observed in the swelling experiments that the 7% KCl solution invaded into core faster than water so that the initial swelling height of clay exposed to 7%KCl solution was more than that exposed to fresh water.This is adverse to wellbore stability and should be further studied.It was found that cations in intercrystallines was bound and ionic exchange can not occure at the stage of crystal layer swelling of clay.So the potassium ion can not effectively prevent the clay layers from swelling.In the process of clay osmotic swelling or in completely dispersing clay,ionic exchange of the cation in intercrystallines can occur so that the potassium ion can effectively prevent the clay crystal layers from osmotically swelling and dispersing and enhance inhibiting effect of fluid.Comparing with osmotic swelling,the swelling pressure of clay is higher and swelling height is smaller and near wellbore formation stress change induced by crystal swelling has significant effect on wellbore stability.