【作者】 周照明；

【导师】 艾池；

【作者基本信息】 大庆石油学院 ， 油气井工程， 2010， 博士

【摘要】 维持稳定的欠压值是欠平衡钻井的核心,气层中采用欠平衡钻进时由于地层气体的侵入,井底欠压值会急剧增大不利于井壁稳定,甚至引起井涌井喷等严重事故,通过加重钻井液密度或井口加回压处理气侵问题时又容易造成井底过平衡,不能达到欠平衡钻井的目的。因此,气层中欠平衡钻进时准确的计算气体侵入量以及气泡在环空中的运移规律是设计并维持安全合理欠压值的关键。本文考虑了地层条件和钻井参数对气体侵入规律的影响,建立了不同地层中的气泡形成尺寸计算模型,根据气泡动力学理论分析了环空中气泡的运移形态及运移规律,从而为气侵过程中合理欠压值的设计及调整提供准确的依据。首先,根据气体在地层中的不稳定渗流机理,考虑了地层条件和机械钻速对气体侵入的影响,建立了欠平衡随钻气侵量计算模型,分析了复合钻速对随钻气侵量的影响,为气泡形成尺寸计算以及运移规律研究提供了必要的参数。其次,通过对气泡形成过程进行受力分析,将气泡形成分为膨胀和脱离两个阶段,建立环空气泡形成模型。针对瞬时气侵量对气泡形成的影响,根据孔口气泡聚并的条件建立临界气侵量计算模型,考虑地层条件和钻井参数等多因素建立气泡形成尺寸计算模型,确定了不同孔隙半径下气泡的脱离频率,根据环空内不同流体的流动规律,考虑了气泡尺寸的影响建立环空中气泡上升速度模型,得出气泡上升速度与气泡生成直径之间的关系,从而为气侵条件下井底欠压值的计算打下基础。再次,应用湍流计算模型以及欧拉多相流计算模型,对单个气泡在环空流场中的变形规律进行了计算分析了钻井液特性对气泡变形的影响。同时,从气泡动力学的角度分析气泡融合的机理,给出了环空气泡融合的条件以及融合速度,从而真实的反映气泡在环空中运移时的形态,为环空气侵钻井液的流型划分提供依据。最后,考虑了不同机械钻速下的岩屑含量以及气侵钻井液的流动规律建立了井底压力计算模型。根据建立的随钻气侵量计算模型、环空气泡生成直径计算模型、气泡融合速度计算模型以及气侵过程中井底压力计算模型,对大庆地区某井欠平衡钻进过程进行了实例计算。采用本文模型所得到的气侵量及井口回压变化规律与实际吻合较好,说明本研究所建立的随钻气侵模型以及气泡形成运移变形模型可以为欠平衡气侵阶段欠压值的合理设计与维持提供必要的依据,具有重要的理论意义和应用价值。更多还原

【Abstract】 Maintain stable voltage value was underbalance pressure drilling′s core, in gas underbalance drill, bottom-hole pressure value would be sharp increased, which against borehole stability, even aroused well blowout and well kick, because the formation gas. Through the mud density or aggravate add back pressure gas handling problems, cannot achieve purpose of underbalance pressure drilling. So accurate calculation gas invasion and air bubbles in the ring of migration rule was the key to the rational and safety underbalance pressure. The reservoir conditions and drilling parameters on the influence of the gas invasion were considered, computational model of bubbles formed dimensions in different formation were established, the migration and rule of bubble rings air were analysed, according to the bubble dynamics theory, and therefore accurate scientific basis for the design of reasonable underbalance pressure in air cushioning were provided.First, according to unstablefiltration theory, the reservoir condition and the penetration rate had a strong effect on gas invasion were considered, calculating model underbalance with drilling were established, drilling rate had impacts on gas drilling were analysed, the requisite parameters were provided for bubbles formed dimensions and the moving rule.Second, model of bubble formation were established, bubble formation was divided into two phases of inflation and departure during bubble formation on force analysis. According to the influence of the instantaneous gas bubbles formation, the calculating model of critical gas were established by bubble coalescence conditions, the geological conditions and drilling parameters were considered, computational model of bubbles formed dimensions were established, bubbles from frequency of the different pore body radius had be determined. Model of the rising velocity of small bubble were established, the bubble size and flow rules were considered, the relations of the rising velocity of bubble and air bubble diameter was obtained, which laied a sound foundation in calculation of bottom underbalance pressure for air cushioning.Again, turbulence modeling and Euler multiphase model were applied, dynamics rule of the single bubble were calculated, and the effects of the drilling fluid propertiesthe on the bubble deformation were analysed. At the same time, the fusion mechanism of bubbles from bubble dynamics were analyed, bubbles in the ring together with the condition and fusion rate, which reflected in the air bubbles during migration, and therefore accurate scientific basis for fluid type of compartmentalizing were provided.Finally, the debris content and flow pattern of gas cut drilling fluid were considered. A bottom hole pressure calculation model was established. According to the established calculation model of gas invaded volume while drilling, the calculation model of gemerated diameter for central air bubble, the speed calculation model of bubble fusion and the calculation model of bottom hole pressure during gas cut, an example of calculation for a well under balanced drilling process was carried out in Daqing area. The gas quantity and well backpressure variation by the present model were well agreed with the actual defects, the model of gascut-while-drilling and the model of bubbles formation, migration and deformation could be provides necessary basis for the rational design of underbalance pressure in gas underbalance stage, the theory was of great theoretical and practical importance.更多还原