深井超深井裂缝性地层致密承压封堵实验研究

深井超深井裂缝性地层钻井过程中极易发生钻井液漏失，桥接堵漏材料形成的裂缝封堵层在高温、高压、高地应力等复杂环境下失稳破坏加剧，导致堵漏成功率和裂缝封堵效果难达预期。基于多级多粒桥接堵漏的思路，以川西地区双鱼石区块超深井钻井常用的WNDK-1型架桥材料和耐高温橡胶颗粒为研究对象，系统开展了高温老化环境下堵漏材料性能评价与裂缝封堵模拟实验。实验结果表明，在150℃钻井液中老化24 h后，WNDK-1型刚性材料的粒度分布未产生明显变化，摩擦系数最高降低1.89%，抗压强度降低1.15%；橡胶颗粒的粒度分布D₉₀值增加3.55%，摩擦系数增加1.59%，抗压强度保持不变；将刚性材料、弹性材料和纤维材料以适当浓度与钻井液复配并进行裂缝封堵，形成的封堵层承压能力普遍高于13 MPa，且封堵层具有低孔低渗特征；观察封堵失稳后裂缝内封堵层结构形态可知，高温老化环境下多级多粒桥接堵漏形成的封堵层主要发生摩擦/复合失稳和剪切错位失稳。

An Experimental Investigation on Pressure Bearing and Tight Plugging of Fractured Formations in Deep and Ultra-deep Wells

Lost circulation is extremely easy to occur during drilling in deep and ultra-deep fractured formations. The failure of plugging zone formed by lost circulation materials (LCMs) may be aggravated under the complex environment of high temperature, high pressure and high in-situ stresses, which results in failure to reach the plugging rate and the fracture plugging effect expectation. Based on the idea of multi-stage and multi-grain bridge plugging, WNDK-1 rigid LCM and high-temperature resistant rubber particles often used in Shuangyushi block located in western Sichuan are selected to conduct LCMs performance evaluation and fracture plugging simulation experiment under high temperature aging environment. The experimental results show that after aging in 150℃ drilling fluid for 24 h, the particle size distribution of WNDK-1 does not change significantly. The maximum friction coefficient and compressive strength of WNDK-1 rigid material decrease by 1.89% and 1.15%. The particle size distribution D₉₀ value of rubber particles increase by 3.55%, the friction coefficient increases by 1.59%, and the compressive strength remains the same. If rigid materials, elastic materials and fibrous materials are mixed with drilling fluid at appropriate concentrations to plug the fractures, the pressure-bearing capacities of the formed plugging zone are generally higher than 13 MPa. Besides, the plugging zone has the characteristics of low porosity and low permeability. The observation of structure and morphology inside fractures after the plugs failure demonstrates that friction/comprehensive failure and shear instability in the plugging zone formed by multi-stage and multi-grain bridge plugging under high temperature aging environment.