页岩气层钻井压力穿透效应研究

页岩段井壁稳定问题是钻井工程中的难点之一,国内外许多学者在研究钻井液与页岩之间的化学势差和水化膨胀作用方面作了大量工作,但对于压力穿透方面的研究工作则相对较少。为此,通过在压力容器中充满钻井液,模拟近井壁过平衡钻井所导致的压力穿透环境,测量压力对垂直于页岩层理和平行于页岩层理方向应变的影响。结果表明,垂直于层理方向的应变随压力增大呈现出显著的阶梯式变化,同一压力作用时页岩压力穿透效应具有时间延迟效应和各向异性。通过理论分析发现,在页岩有效孔隙度一定的条件下,页岩压力穿透效应主要受滤饼渗透率、钻井液液柱压力与地层孔隙流体压力之间的压差、页岩与钻井液接触时间以及钻井液黏度的综合作用。页岩压力穿透效应对研究页岩段钻井过程中井壁稳定与控制具有重要意义。

Research for the mechanism of pressure penetration effectduring the drilling in shale gas formation

One of the most difficult problems in drilling engineering is shale wellbore stability. Many scholars home and abroad have done a lot of work in the chemical potential difference and hydration expansion between drilling fluid and shale, but relatively done few work for pressure penetration. Therefore a pressure vessel filled with drilling fluids is developed in this paper to simulate the shale pressure penetration environment near-wellbore due to the overbalance drilling. And then test the strain that perpendicular and parallel separately to the shale bedding. The result shows that the strain perpendicular to the shale bedding has a significantly large step change as pressure increasing. And pressure penetration shows a significant time delay effect and aeolotropism under the same pressure environment. Theoretical analysis shows that shale pressure penetration is mainly affected by the permeability of mud cake, pressure between the drilling fluids and the formation pore fluids, contact time of shale and drilling fluids, as well as drilling fluid viscosity when the effective porosity in shale is a constant. Shale pressure penetration effect is significant to the study of wellbore stability and controlling in shale drilling process.