欠平衡钻井期间地层流体流入规律研究

THE RESEARCH OF FEATURE OF FORMATION FLUID INFLUX DURING UNDERBALACED DRILLING

为了从理论上研究欠平衡钻井过程中的一些问题 ,以便更好的控制和发展欠平衡钻井。本文研究了地层流体流入井筒的规律 ,建立了欠平衡钻井期间井底流压计算方法 ,指出了假设油气层厚度不变下模拟欠平衡钻井期间地层流体流入井筒的理论有较大误差。给出了在欠平衡钻井期间 ,随着井眼不断加深 ,油气藏暴露面积不断加大 ,地层流体流入井眼的参数计算方法。在此基础上 ,提出了在欠平衡钻井期间 ,保持井底负压差钻井会因地层流体流入井筒过多而造成控制困难 ,而根据地层渗透率与钻速 ,采用恒地层进气量钻井将是安全的。

Underbalanced drilling has been more and more utilized to minimize problems associated with invasive formation damage which often greatly reduce the productivity of oil and gas reservoirs.However,in many underbalanced drilling operations,additional benefits are not seen due to the difficulty of safely controlling the bottom hole pressure difference.Damage due to poorly designed and/or executed underbalanced drilling programs can rival or even greatly exceed that which may occur using a well_designed conventional overbalanced drilling program.A method for calculating the bottom hole flowing pressure during underbalanced drilling has been developed which takes into account all important factors contributing to this process.This transient,one_dimensional multi_phase flow method is closer to the true than conventional ones which consider the constant formation thickness as an assumption during drilling.Taking into account the changes of the formation thickness in calculating the BHFP,in addition author put forward the original viewpoint that keeping constant gas invasive velocity is safer than the traditional one that keeps the constant bottom hole pressure.We can safely draw the conclusion that it is possible to calculate and control the volume of gas influx if the method discussed in this paper is used during underbalanced drilling.