出砂水平井近井塑性区出砂半径预测研究

基于地层岩石弹塑性变形理论,建立出砂水平井近井塑性区应力分布模型.根据弹性区与塑性区边界应力连续的原理,提出水平井弹塑性区边界即塑性出砂半径的预测模型与方法,分析了出砂水平井近井塑性区应力分布规律及出砂半径的敏感性因素.结果表明:水平井塑性应力分布及出砂半径与原始主应力关系、井周角、井斜方位角、流压等参数有直接关系;塑性出砂半径随井周角的变化规律与原始垂向主应力和最大水平主应力的大小关系有关,当最大水平主应力较大时,井周铅垂方向的出砂半径大于水平方向的出砂半径,即铅垂方向更容易出砂,当垂向主应力较大时则相反;随着井斜方位角变化出砂半径呈周期性变化,在原始水平最大主应力σH大于垂向主应力σv的情况下,井斜方位角为0°和180°时,水平方向出砂半径较大,更容易出砂;井斜方位角为90°和270°时,铅垂方向更容易出砂;由于岩石力学参数及地应力的非均质性分布,水平井出砂半径沿着井身轨迹方向也表现出明显的非均质性.

Distribution of plastic stress near wellbore and prediction of sanding radius for sanding horizontal wells

Based on the rock elastic and plastic deformation mechanisms,a systematic formation stress distribution model was evolved to study the plastic zone in sanding horizontal wells.According to the principle that the stress keeps continuous at the boundary between the elastic and plastic zones,a new model for the plastic sanding radius,which is the real boundary of elastic and plastic zones,for sanding horizontal wells was proposed.Using this model,the factors affecting the distribution of stress in plastic zone near a sanding horizontal well and the corresponding sanding radius were analyzed.The results show that in a sanding horizontal well,the plastic stress distribution and sanding radius are related to the prime principal stress,circumferential angle,drift azimuth and bottom hole flowing pressure.The relationship between plastic sanding radius and circumferential angle is directly affected by the relative magnitudes of the prime maximum horizontal principal stress and vertical principal stress.In case of high horizontal principal stress,the sanding radius in vertical direction is higher than that in horizontal direction,which means more severe sanding in vertical direction.In the case of high vertical principal stress,the law reverses correspondingly.The sanding radius varies periodically with drift azimuth.In a horizontal well with drift azimuth of 0°and 180°,the sanding radius keeps higher in horizontal direction than vertical,which means more severe sanding tendency.In case of 90°and 270° drift azimuth,the sand will be produced more seriously from vertical direction.Additionally,due to the heterogeneity distribution of rock property along wellbore trajectory,the distribution of stress and sanding radius reveal the same heterogeneity distribution characteristics.