气基流体钻井气液流量组合设计新方法及应用

欠平衡钻进时井底压力较高,会引起储层的伤害,而接单根时井底压力较低,将引起井眼的破坏,而井底压力可由气体和液体流量组合来控制。为了使欠平衡钻井中储层伤害和井眼失稳之间的矛盾最小化,给出了一套在给定地质、钻井条件下进行充气欠平衡钻井气液流量组合设计新方法,该方法利用欠平衡钻井井筒4相流体动力学模型,将已确定的井底压力安全窗口转换为地面气液体注入流量的安全窗口。此流量安全窗口中,地层孔隙压力限制了窗口曲线的上界,井眼坍塌压力为窗口曲线的下界,并由钻井液的携岩能力和井壁冲蚀曲线封闭而成。此设计方法采用电子表格软件绘制气液流量安全窗口,可直观地选择最优流量组合。使用该设计方法对新疆石南油田SN4003井的充氮气欠平衡钻井进行优化设计,并与钻井实效对比评价,证明了该方法较为可靠、实用。

New design approach on combination of liquid-gas flow rates of gas based fluid

During Underbalanced Drilling(UBD),the highest bottom hole pressure during normal drilling condition affects the degree of formation damage,the lowest bottom hole pressure during pipe connection controls severity of the wellbore damage.And bottom hole pressure is controlled by the combination of the liquid and gas flow rates on the ground.In order to minimize both the formation damage and wellbore damage problems,it is highly desirable to have an easy-to-use approach to generate balanced design of combinations of liquid and gas flow rates under given drilling conditions.Based on the four phases fluids dynimics model,the design method could convert security window of bottom hole pressure to the security window of combination of the liquid and gas flow rates on the ground.The method adopted Excel Sheet to protract the window,and could choose the optimum combination.In the liquid-gas rate window,formation fluid pressure limits the upper bound of the flowing bottom hole pressure and wellbore collapse pressure was the lower bound of the circulation-breaking bottom hole pressure.The window was closed by fluid's cutting carrying capacity and wellbore washout criteria.And to verify the new approach,an illustrative example(SN4003) was presented in this paper to demonstrate how to use the new design method.this successful UBD field case was reviewed and compared with the optimum design results.Good consistency was indicated.