气体吸附对煤层安全钻井液密度的影响

发布时间：2019-02-08 19:37

【摘要】：煤岩中割理极为发育,导致煤层非均质性极强,在煤层钻井过程中井壁极易垮塌,掩埋钻具,钻井过程中配置合理的钻井液用以保持井壁稳定具有重要的意义。现阶段主要是运用经典连续介质理论模型进行钻井过程中安全钻井液密度窗口预测,导致现场实际效果较差。实际煤层不仅割理发育并且大量CH4以吸附态赋存于煤层中,将弱化煤岩力学强度,使原本就易失稳的井壁越加不稳定。因此,针对煤层为非连续介质的特殊性,基于非连续介质力学构建的离散元模型分析钻井过程中煤层井壁稳定性,并结合连续介质强度分析法在考虑气体吸附对煤岩力学强度弱化影响的情况下,用以确定煤层最佳防塌钻井液。最后,根据山西省宁武盆地的煤岩数据及现场钻井液资料,利用上述理论进行实例计算,指出研究区煤层防塌需保证钻井液密度大于1.009 g/cm3,并且需在钻井液中添加暂堵剂以提高其封堵能力。
[Abstract]:The cleat in coal and rock is very developed, which leads to the strong heterogeneity of coal seam. It is of great significance that the borehole lining is easy to collapse in the process of coal seam drilling, the drilling tool is buried, and the reasonable drilling fluid is allocated during drilling to maintain the stability of the well wall. At the present stage, the classical continuum theory model is mainly used to predict the density of safe drilling fluid in drilling process, which results in poor actual effect on the spot. The actual coal seam is not only cleat development but also a large amount of CH4 exists in the coal bed as adsorption state, which will weaken the mechanical strength of coal and rock and make the shaft wall which is easy to be unstable become more unstable. Therefore, according to the particularity of discontinuous medium, the discrete element model based on discontinuous medium mechanics is used to analyze the stability of coal seam wall during drilling. Considering the influence of gas adsorption on the weakening of mechanical strength of coal and rock, the continuous medium strength analysis method is used to determine the best sloughing prevention drilling fluid in coal seam. Finally, according to the data of coal and rock and field drilling fluid data in Ningwu Basin, Shanxi Province, and using the above theory to carry out practical calculation, it is pointed out that the density of drilling fluid must be greater than 1.009 g / cm ~ 3 in order to prevent coal seam sloughing in the study area. And the temporary plugging agent should be added to the drilling fluid to improve its plugging ability.
【作者单位】：中国石油塔里木油田分公司油气工程研究院;西南石油大学油气藏地质及开发工程国家重点实验室;
【分类号】：TE254.2

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