井漏失返MWD无信号原因分析

Analysis of the Causes of MWD Signal Loss Due to Well Leakage and Return Flow

摘要: 在复杂地质条件下的油气勘探开发过程中，低压地层的钻探作业常面临严峻挑战，其中井漏和随钻测量(MWD)信号丢失是两大关键难题。当钻遇低压易漏地层时，钻井液大量漏失导致井筒内液柱压力下降，严重时发生“失返”现象，即循环系统无法建立有效循环，钻井液无法从井口返出。在此工况下，泥浆脉冲MWD系统往往出现信号传输中断或完全无信号，严重影响实时地质导向与工程决策。本文以实际钻井案例为基础，结合流体力学、信号传输理论及现场实践经验，系统分析了低压钻井发生井漏失返后MWD无信号的根本原因。研究指出，主要影响因素包括：井筒内有效循环通道丧失导致泥浆脉冲无法传播；环空液面大幅下降致使信号衰减加剧；钻具结构与井眼几何形态变化对声波/压力波传播路径的干扰；以及地面传感器因流体流量不足而无法捕捉微弱信号等。通过建立简化物理模型与数值模拟，验证了上述机理。最后，提出了针对性的应对策略，包括优化钻具组合设计、采用电磁MWD或正脉冲系统、强化堵漏技术、实施间歇式信号发送模式等。本研究成果对于提高复杂地层钻井安全性、保障随钻数据连续性具有重要指导意义。

Abstract: In the process of oil and gas exploration and development under complex geological conditions, drilling operations in low-pressure formations often encounter severe challenges, with well leakage and the loss of measurement-while-drilling (MWD) signals being two key problems. When encountering low-pressure and easily leaking formations, a large amount of drilling fluid leaks, causing a drop in the liquid column pressure in the wellbore. In severe cases, the “loss of return” phenomenon occurs, meaning that the circulation system cannot establish an effective circulation and the drilling fluid cannot return to the surface. Under such conditions, the mud pulse MWD system often experiences signal transmission interruption or complete loss of signal, seriously affecting real-time geological steering and engineering decision-making. Based on actual drilling cases, combined with fluid mechanics, signal transmission theory, and field practical experience, this paper systematically analyzes the fundamental reasons for the loss of MWD signals after well leakage and loss of return in low-pressure drilling. The research points out that the main influencing factors include: the loss of effective circulation channels in the wellbore, which prevents the propagation of mud pulses; the significant drop in the annular liquid level, which intensifies signal attenuation; the interference of the drill string structure and wellbore geometry changes on the propagation path of acoustic and pressure waves; and the inability of surface sensors to capture weak signals due to insufficient fluid flow. Through the establishment of a simplified physical model and numerical simulation, the above mechanisms were verified. Finally, targeted countermeasures were proposed, including optimizing the drill string assembly design, adopting electromagnetic MWD or positive pulse systems, strengthening well control technology, and implementing intermittent signal transmission modes. The research results have significant guiding significance for improving the safety of drilling in complex formations and ensuring the continuity of MWD data.