【作者】 程荣超；

【导师】 王瑞和；

【作者基本信息】 中国石油大学 ， 油气井工程， 2008， 博士

【摘要】 作为保护油气层、减少钻井风险、降低钻井成本和提高单井产量的一项重要技术,欠平衡及控压钻井技术已在全球范围之内引起石油公司的普遍兴趣。作为该技术的重要分支,水平井泡沫钻井技术作为当前和未来可以预见的用于提高油气藏勘探开发综合效益的有效手段,国外现场应用较多,而国内尚处于起步阶段。因此,开展有关泡沫流体水平井段流动特性的研究对于提高国内窄密度窗口安全钻进技术水平和推进科学化钻井进程具有十分重要的现实意义。论文在大量调研的基础上,应用流动相似理论和量纲分析方法,成功设计并研制了新型多功能井筒流动模拟实验架,可对可压或不可压的牛顿或非牛顿流体的环空流动性能进行可视化实验研究,能同时实现升温升压、恒速加砂、钻杆转动、偏心、倾斜及实验参数的实时控制与显示,形成了一套实验研究气基流体井筒流动特性的新方法。在此基础上,利用管式流变仪和环空实验段分别研究了泡沫流体的流变性能和携岩性能。基于Oldroyd-Jastrzebski滑移修正方法和体积当量原则,利用曲线拟合和非线性回归方法建立了考虑和不考虑壁面滑移时的幂律型泡沫流变参数预测关联式和滑移系数修正关系式,研究了聚合物浓度、温度和压力对流变参数的影响规律。利用定量岩屑床法和恒速同步加砂法实验研究了岩屑床的运移、破坏模式以及不同流动参数对泡沫携岩临界返速和环空岩屑浓度的影响规律。将泡沫流体处理为一类特殊的非牛顿两相可压流体,利用有限元和力学分析法建立了泡沫在钻杆和同心环空内的流动控制方程,对不同工况下水平钻杆与环空内的压降与流速的分布特征进行了计算与分析。利用恒定回压法和逆循环迭代法建立了水平井泡沫钻井过程中井筒循环压力的计算方法,开发了相应的应用程序。对一口水平井的模拟计算结果与现场实际吻合,验证了计算方法的正确性和可行性。利用分形几何理论建立了描述岩屑粒径分选性的颗粒级配模型,提出了相对沉没度随机变量和等效粒径的概念,通过滚动力矩平衡理论建立了考虑位置随机性和形状不规则性的岩屑床表面颗粒起动机制,在临界环空返速与颗粒起动标准之间建立了定量关联式。将临界返速预测值与实测值进行了对比,认为均匀颗粒临界起动速度对应的定量起动标准在40%左右比较合适,不均颗粒的临界起动速度存在分级性,细颗粒较同径均匀颗粒难起动,粗颗粒较同径均匀颗粒易起动。根据临界井斜角理论将水平井分为水平及近水平段、过渡段和垂直及近垂直段三段,基于守恒律和力学分析方法建立了适用于水平井全井筒的泡沫携岩一维稳态理论模型,以变步长推进迭代方法对模型进行了数值求解。此外,考虑层间质量传递和地层流体的侵入,建立了水平段泡沫携岩的一维瞬态双层流动模型,采用修正的SIMPLE算法对模型进行了数值求解,并通过多元非线性回归建立了水平井段临界返速(CFV)和最优气液流量的优化设计方法。数值模拟结果与本文的实验结果吻合较好,证明所建立的泡沫携岩理论模型正确可靠,从而为水平井泡沫钻井的井筒压力控制和井眼净化技术提供了理论依据。更多还原

【Abstract】 Because of the advantages in oil and gas reservoir protection, drilling risk diminution, drilling cost reduction and individual well production improvement,Underbalanced Drilling and Managed Pressure Drilling have been attracting more and more attention from oil companies all through the world. Foamed horizontal drilling, as an important branch of the technique, is proved to be one of the effective methods that can be predicted to improve the overall exploratory development benefit. Though UBD and MPD have been applied extensively in field abroad, related research is still on a preliminary stage in China. Therefore, research on the flow behavior of foam fluid in horizontal well section is of practical importance in improving the narrow-window safe drilling technology and promoting the scientific drilling proceeding in China.Based on extensive literature review, using flow similarity theory and dimensional analysis, a new multi-functional wellbore flow simulation loop was successfully designed and developed. The flow loop can be used to visually measure the flow behavior of compressible or incompressible Newtonian or non-Newtonian fluid. It simultaneously allows the temperature and pressure elevation, sand injection with constant speed, inner pipe rotation, eccentricity, inclination, and real-time control and indicating of experimental parameters. A new approach to studying the wellbore flow performance of gasified drilling fluid was finally obtained. Then the rheological property and cuttings transport capability of foam fluid were studied respectively using the pipe flow viscometer and annular test section of the flow loop. On the basis of Oldroyd-Jastrzebski slip correction method and volume equalized principle, the slip corrected and non-corrected correlations for rheological parameters of power low model of foam fluid were established by means of curve fitting and nonlinear regression, and the effects of polymer concentration, temperature and pressure on rheological parameters were studied. Meanwhile, using quantitative cuttings bed method and constant-speed synchronous sand injection method, the cuttings bed transport and erosion mode were observed, and the influence of different flow parameter on critical annular flow velocity and cuttings concentration were experimentally studied.Foam fluid was considered as a special non-Newtonian compressible fluid. The governing equations for foam flow in concentric annulus and drill pipe were derived by means of finite element and mechnical analysis, and the pressure gradient and flow velocity were calculated under different operational conditiond. The wellbore pressure calculation method in foamed horizontal drilling was then proposed using constant back prssure and reversal circulation iteration, and relevant application program was developed. Simulation results on a in-situ horizontal well agree well with field practice, hence the proposed calculation method was proved to be correct and reliable.A particle grading model for cuttings size distribution was established using fractal geometry theory. The concepts of relative submergence and equivalent diameter were proposed. Taking the location randomness and geometry irregularity into consideration, the particle starting mechanism on the cuttings bed surface was studied in the light of rolling moment balance, and relevant correlation between critical flow velocity and particle starting criterion was obtained. Comparison between theoretical predictions and test results shows that the quantitative starting criterion is proved to be about 40% that is appropriate for correspondent critical starting velocity for uniform particles. For non-uniform particles with starting velocity gradation, compared with uniform particles of the same diameter, it is more difficult for fine particles to start moving but easier for the coarse particles.According to the concept of critical inclination angles, the horizontal well was divided into three segments, i.e. the horizontal and near horizontal section, vertical and near vertical section and transitional section. A one-dimensional stable theoretical model for cuttings transport with foam, appropriate for the entire horizontal wellbore, was established based on the conservation law and mechanical analysis. The progradational iteration method with variable step length was used for numerical calculation for the proposed model. Meanwhile, considering the interlayer mass transmission and formation fluid infiltration, a one- dimensional transient two-layer flow model was proposed for cuttings transport with foam in horizontal section. The model was numerically calculated with the corrected SIMPLE algorithm. Then, an optimized design method for critical flow velocity (CFV) and optimum gas/liquid flow rate in horizontal well section was established by multivariate nonlinear regression. Theoretical predictions by numerical simulation agree well with the experimental results in this dissertation, which validates the correctness and reliability of the proposed models for cuttings transport with foam fluid. Research results offer theoretical foundations for wellbore pressure control and hole cleaning technology in foamed horizontal drilling.更多还原