为了改善径向水平井水力破岩和携砂效果，以多相流理论为基础，借鉴欠平衡钻井基本原理，把欠平衡技术引入到径向水平井设计和施工中，研究了径向水平井施工中压力控制问题，建立了径向水平井施工的物理模型和气混两相流动模型，并对径向水平井施工中注气量对井内压力的影响关系和规律进行了计算和分析。结果表明，氮气的注入可以有效降低井底压力，同时利用充氮气钻井液可同步携带岩屑返出地面；井底压力与注气速度和钻井液排量有关，注气速度越大，钻井液排量越小，井底压力降低幅度越大；环空岩屑只有当钻井液排量达到一定时，配合适当的注气速度才能被安全携带出地面。研究结果为进行径向水平井欠平衡施工的设计提供了理论依据。%In order to improve the hydraulic breaking rock ability and sand carrying effect in radial horizontal well, based on the multiphase flow theory, underbalanced drilling technology was introduced into the design and drilling of new type radial horizontal well by using the basic principle of underbalanced drilling. Research on the pressure control during construction was conducted, and physical model and two phase (gas-liquid)flow model were established to calculate and analyze the relationships and rules of the amount of gas injection and wellbore pressure of radial horizontal well In the process of construction. As conclusion, nitrogen injecting can effectively decrease bottom hole pressure (BHP), and drilling fluid mixed nitrogen could help carrying rock fragments flow back to ground; BHP not only related with gas injection speed but also related with the flow rate of base fluid, which means that higher gas injection speed and smaller fluid rate greatly reduce BHP; annular cuttings with appropriate gas injection rate will carry out of the ground only if the drilling fluid volume reaches a certain value. This conclusion will provide a theoretical basis for construction design of new type radial horizontal well.
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