不规则井眼固井环空流动压降变化规律

Change law of annulus flow pressure drop in irregular borehole cementing

在窄密度窗口地层固井作业中,经常出现井漏、地层流体侵入井筒等复杂情况,因此,针对固井环空压力剖面的精细计算与控制十分重要,有助于促进固井施工安全。在实际钻井过程中,受地层纵向非均质性的影响,井径扩大不均匀容易形成“大肚子”等不规则井眼,其直接影响固井流场及环空压力剖面,目前针对这种不规则井眼的固井环空流动压降计算方法较少。针对井径此类不规则井眼,通过建立不规则井眼条件下的流动压降方程分析了流动压降构成,建立了环空流体流动控制方程,确定了求解方法,并开发软件进行了计算分析,得到了不同井径扩大率条件下不规则井眼的固井环空流动压降变化规律,并运用Fluent数值模拟软件进行了验证。研究结果表明,在同等井径扩大率条件下,流体排量越大,不规则井眼段流动压降越大;在常见的井眼扩径范围内,“大肚子”井眼段流动压降小于正常井眼段流动压降,软件计算结果与数值模拟结果偏差在工程允许误差范围内。该方法可以为精细计算固井环空压力剖面提供技术手段。

In the cementing operation for formation with narrow density window,complex situations such as lost circulation and formation fluid intrusion into wellbore often occur.Therefore,it is very important to calculate and control the annular pressure profile of cementing accurately,which helps to promote the safety of cementing operation.In the actual drilling process,due to the influence of longitudinal heterogeneity of formation,uneven diameter expansion tends to form the irregular boreholes such as“big belly”,which directly affects the flow field and annular pressure profile.At present,there are few methods to calculate the pressure drop of annular flow for such irregular boreholes.Aiming at such irregular boreholes,the composition of flow pressure drop was analyzed by establishing the flow pressure drop equation under the condition of“big belly”holes,the annulus fluid flow control equation was established,and the solution method was determined;Then the software was developed for calculation and analysis,the change law of annulus flow pressure drop in irregular boreholes with different hole diameter enlargement rates was obtained,and the results were verified by the numerical simulation software,Fluent.The results show that the larger the flow displacement is,the greater the flow pressure drop is in the irregular borehole under the condition of the same diameter enlargement rate;The flow pressure drop of the“big belly”borehole is less than that in normal boreholes within the scope of common hole enlargement rates;The offset between software calculation results and numerical simulation results is within the allowable error range of engineering.This method can provide a technical means for calculating the annular pressure profile of cementing.