【作者】 冯福平；

【导师】 艾池；

【作者基本信息】 东北石油大学 ， 石油与天然气工程， 2014， 博士

【摘要】 注水泥顶替界面边界描述了环空钻井液的滞留位置，顶替界面形状反映了迟流引起的两相流体掺混程度，钻井液的滞留和迟流都会造成环空封隔能力的降低，因此通过分析注水泥顶替界面的边界及形状优化顶替参数从而降低偏心环空钻井液的滞留和迟流程度是获得良好固井质量的关键。现有注水泥顶替理论无法描述偏心环空边壁附近顶替界面的位置，并且没有考虑两相流体的密度差产生的驱动力沿周向角和半径的变化对顶替界面形状的影响，针对这一问题本文进行了偏心环空注水泥顶替界面边界及顶替界面形状描述模型研究，主要研究内容包括：（1）选取赫巴流变模式作为钻井液和水泥浆流变模式的描述模型，分析了赫巴流体在偏心环空中的流动特征，得到了偏心环空赫巴流体区域整体滞留范围，建立了赫巴流体在偏心环空不同周向角和半径处的流速分布模型；（2）采用顶替界面微元力学分析的方法，建立了偏心环空注水泥顶替界面边界位置计算模型，阐明了偏心环空钻井液滞留机理，揭示了偏心环空套管和井壁处钻井液滞留的规律；建立了偏心环空井壁和套管处钻井液零滞留条件计算模型，为固井环空零滞留顶替钻井液、水泥浆性能以及顶替参数的调整提供了理论依据；（3）考虑了顶替界面上两相流体的密度差所产生的驱动力沿周向角和半径的变化，建立了考虑扩散效应时的顶替流体浓度分布模型和不考虑扩散效应时的动态顶替界面形状描述模型，反映了顶替流体沿环空轴向和周向的二维流动特性，能够准确描述不同时刻固井顶替界面在环空中的整体形态；（4）分析了环空周向流作用下固井稳定顶替界面的形成机理，根据稳定顶替时顶替界面上流函数的分布特征和流体运动方程建立了套管居中及偏心条件下稳定顶替界面形状描述模型，揭示了直井及斜井稳定顶替界面形状的变化规律，得出了套管偏心度、井斜角与顶替流体密度差之间的合理匹配关系，并通过数值模拟方法进行了验证。本文通过偏心环空注水泥顶替界面边界及顶替界面形状的研究揭示了环空钻井液的滞留机理和迟流规律，完善了固井二维顶替界面形状描述模型，丰富了注水泥顶替理论；得出了套管偏心度、井斜角与顶替流体密度差之间的合理匹配关系，为偏心环空注水泥顶替参数的优化设计提供了理论依据，有助于延长油气井的使用寿命，提高分层注采压裂等增产措施的实施效果。更多还原

【Abstract】 During cementing, the displacement interface boundary describes the retention positionof annular drilling fluid and the displacement interface shape reflects the intermixing extent oftwo-phase fluids caused by late-flow. There is no doubt that the retention and late-flow ofdrilling fluid can result in the decrease of annular isolation ability. Therefore, decreasing theretention and late-flow extent of drilling fluid by optimizing the displacing parameters on thebasis of analyzing displacement interaface boundary and shape is the premise to obtain goodcementing quality. Unfortunately, the present cementing theory can’t involve the study ofdisplacement interface position on the annular walls. Moreover, it can’t take the effect ofdriving force generated by density difference which changes with azimuthal angle and annularradius on the dispalcement interface shape into consideration. In order to solve the problem,this paper conducts a research on the calculation model of displacement interface boundaryand shape during cementing in eccentric annulus, which mainly includes that:(1) Herschel-Bulkely model is chosen to describe the rheological behavior of annularslurry and drilling fluid. Then the flow characteristics of Herschel-Bulkely fluid in theeccentric annulus is analyzed. Finally, the overall range of drilling fluid retention is obtainedand the distribution model for fluid flow rate in different azimuthal angle and annular radius isestablished.(2) A model for calculating the boundary position of drilling fluid retention layer isestablished with the method of mechanism analysis on displacement interface element, whichreveals the mechanism of drilling fluid retention during slurry displacing in eccentric annulus.On the basis of the model, the distribution in different azimuthal angle of drilling fluidretention on casing and well walls is obtained. In order to insure the drilling fluid to beadequately displaced, the non-retention model is established, which provides a theoreticalbasis for the adjustment of drilling fluid and slurry rheological parameters and displacingparameters that can achieve non-retention with no doubt.(3) By taking the change of driving force generated by the height difference betweentwo-phase fluids along annular azimuthal angle and radius, the calculation model includingdiffusion effect for displacing fluid concentration and the description model excluding diffusion effect for displacement interface shape are established respectively. Obviously, thetwo models indicates the flow behavior of displacing fluid in the azimuthal and axialdirections, therefore, which can the overall shape of displacement interface in the annulus atdifferent time.(4) The formation mechanism of steady displacement interface under the effect ofazimuthal flow is analyzed. Moreover, the description models for steady displacementinterface in concentric and eccentric annulus are established respectively. The two models canillustrate the change rule of steady displacement interface shape in the vertical and deviatedwells. Finally, the matching relationship between casing eccentricity, deviation angle anddensity difference is obtained. Besides, it is verified by the numerical simulation results.The retention mechanism and late-flow law of annular drilling fluid are revealed bystudying on the displacement interface boundary and shape during cementing in eccentricannulus. As a result, it improves the two-dimensional description model for displacementinterface shape and enriches the cementing theory to some extent. Furthermore, the matchingrelationship between casing eccentricity, derivation angle and density difference is obtained inthis paper, which provides a theory basis for the optimization design of displacing parameterswith no doubt. Obviously, the improvement of cementing quality is beneficial for prolongingthe oil and gas wells life-span and enhancing the implementation effect of zonal fracturing.更多还原