注空心球多梯度钻井气侵快速识别分析

为研究注空心球多梯度钻井中分离器位置等关键参数对气侵识别时间的影响，文章考虑多梯度钻井参数、井筒与地层间能量交换对井筒内混合流体的物性参数、气液两相流的瞬态传热过程与流动规律的影响，建立了多梯度钻井瞬态气液两相流新模型，研究了不同多梯度参数对气侵识别时间和井底压力的影响规律，并对在不同影响因素条件下的气侵时间进行了无量纲对比分析。结果表明：在不同空心球体积分数、密度或分离器级数条件下，溢流量和井底压力变化包括“线性分布”和“指数分布”2个阶段；在不同分离器位置条件下，溢流量和井底压力变化包括2个“线性分布”阶段和1个“指数分布”阶段；指数阶段中钻井液池递增速率显著增大可以作为气侵识别的早期信号；0.8 m³溢流量作为气侵监测的阈值时，空心球体积分数的影响最为显著，其溢流量变化规律作为气侵早期监测的依据会更准确；分离器数量的影响程度最小。该研究成果可以为注空心球多梯度钻井的早期气侵监测提供理论参考，对下一步的井筒压力有效干预提供重要依据。

Analysis of Fast Identification for Gas Invasion in Multi-gradient Drilling by Hollow Glass Sphere Injection

In order to study the influence of key parameters on gas invasion identification time under the condition of gas invasion based on multi-gradient drilling by hollow glass spheres (HGS) injection, a new transient gas-liquid two-phase flow model for multi-gradient drilling is established in this paper, by considering the physical parameters of the mixed fluid in the wellbore, the transient heat transfer process and flow rules of gas-liquid two-phase flow under the multi-gradient parameters and the energy exchange between the wellbore and the formation. The implicit finite difference method and double-cycle iteration method are used to analyze the model based on the same overflow threshold condition, the effects of different multi-gradient parameters on gas invasion identification time and bottom hole pressure are studied. Finally, the principle of variation coefficient weighting method is introduced to conduct a dimensionless comparative analysis of gas invasion time under different influence factors. The results show that under the conditions of different HGS density, volume fraction or separator stage, the change of overflow and bottom hole pressure includes two stages:“linear distribution” and “exponential distribution”. Under the conditions of different separator positions, the change of overflow and bottom hole pressure includes three stages: “2-stage linear distribution” and “ exponential distribution”; In the exponential change stage, the increasing rate of mud pit increment will increase significantly, which can be used as an early signal for gas invasion identification. According to the results of dimensionless analysis, taking 0. 8 m 3 overflow as the gas invasion monitoring threshold,the HGS volume fraction has the most significant impact, and the number of separators has the least impact. Therefore, the change rule of the former overflow will be more accurate as the basis for early gas invasion monitoring. The research results can provide a theoretical reference for the early gas invasion monitoring of multi-gradient drilling by HGS injection, and also provide an important basis for the early detection of gas invasion anomalies and effective intervention of the next wellbore pressure.