小间隙井注水泥环空流动计算方法与应用

A calculation method of annular flow pressure for small clearance cementing and its application

非常规井身结构中小间隙与小井眼段的注水泥环空流动与常规井眼有很大出入,采用常规流动计算方法来分析小间隙流动,则会造成很大的误差,影响到作业安全。为此,分析了小间隙对环空流态、流动阻力的影响,从理论上系统研究了小间隙注水泥流动的流态判别、偏心效应系数、摩阻系数等关键参数的计算方法,并提出了相应的修正方法:小间隙环空的水泥浆流变参数计算,应使用旋转黏度计600转和300转的读值进行流变参数计算,进而综合考虑流态、偏心、环空尺寸等影响因素,将环空进行分段,建立了深井固井环空流动摩阻计算模型。在中国西部地区应用了5口小间隙井,固井套管下入深度达到6 000m,小间隙井段长度达到2 000m,采用该修正方法计算的压力值和实际施工压力值的误差控制在1.5MPa以内,很好地满足了生产要求。

The cementing annular flow pressure of small clearance and slimhole sections in an unconventional well is greatly different from that in a conventional borehole.If the regular calculation method of annular flow pressure for conventional borehole is used to analyze the flow of small clearance,the resulted big error will bring about a negative effect on the safety of cementing.Therefore,this paper first analyzed the impact of small clearance on the flow regime and flow resistance of annular fluid,then systematically studied the calculation method of key parameters such as the determination of flow regime,eccentric effect coefficient,friction resist ance coefficient,and finally proposed a corresponding modified approach.In detail,the parameters of small clearance annular flow-pressure cement flow regime were calculated by a rotating viscometer with the reading value of 600 and 300 revolutions respectively.In addition,taking the impacts of flow regime,eccentricity and annular size into account,we established the friction resistance calculation model for the deep well cementing annular flow pressure by segmenting the annular flow pressure.In a few pilot tests of five small clearance wells selected from the western fields in China,and with a cementing casing run into small clearance well sections of 6000 m deep and 2000 m long,the errors between the pressure calculated with this modified approach and the actual measured pressure values were controlled within 1.5 MPa,which totally met the production requirements.