注水泥顶替环空钻井液滞留角度优化计算

OPTIMAL CALCULATION ON DRILLING FLUID RETENTION ANGLE IN ECCENTRIC ANNULUS DURING CEMENTING DISPLACEMENT

在油气井固井注水泥过程中,由于套管偏心,井眼环空各间隙处钻井液被水泥浆顶替的情况不同,窄间隙处的钻井液受到较大的阻力而容易滞留。为了保证固井质量,从流体受力分析出发,研究了水泥浆与钻井液密度差以及流体流变性能等因素对注水泥顶替效率的影响规律,建立了偏心环空内的钻井液滞留角度范围模型。采用"高斯数值积分结合弦割法"对该模型进行了数值求解,结合现场实际情况,计算了不同固井工况下的截面顶替效率,进而定量求得钻井液零滞留时的驱动压力梯度。对于直井和大斜度井,通过增大水泥浆与钻井液的密度差、降低钻井液静切力以及提高水泥浆动切力均有利于改善大斜度井和水平井内的注水泥顶替效率。

In process of cementing,the displacement condition in each annular gap is different due to casing eccentricity,drilling fluid retention in the narrowest gap. In order to guarantee cementing quality,the influence of factors,such as density difference between drilling fluid and cement slurry and fluid rheological properties on cementing displacement efficiency were analyzed. The retention angle range model about drilling mud in the eccentric annulus was founded. Gauss numerical integration method combined with chord secant method were used to solve the model. By use of practical data,the displacement efficiency aiming at different cementing condition was calculated and the proper pressure gradient when drilling fluid left in the annulus was got. The study results showed that increasing density difference and cementing slurry dynamic shear force,decreasing drilling fluid yield stress were beneficial to improve displacement efficiency in highly- deviated well and vertical well.