东营组硬脆性泥页岩井壁稳定性研究

硬脆性泥页岩地层的钻井过程中,井壁垮塌现象频发,严重影响了油气田的高效开发。为减少该类地层井壁失稳问题,本文通过室内试验对硬脆性泥页岩理化特性进行分析,并定量分析钻井液作用对泥页岩影响程度。基于室内试验结果,利用线弹性理论和单一弱面准则,建立了考虑弱面结构、温场作用、水化特性的井壁稳定模型。利用该模型对井壁稳定性影响因素进行分析,结果显示：弱面结构的存在使得坍塌压力明显升高。弱面产状变化,造成坍塌压力分布复杂,不再存在单调变化的井斜方位；随温差增大,造成地层坍塌压力上升,但上升幅度相对较小；钻井液作用会显著缩减安全钻井方位范围,提高井壁垮塌风险。现场实例分析结果表明：利用提出的井壁稳定模型可以准确地预测坍塌压力分布,从而指导现场钻井作业。

The research on wellbore stability in hard brittle shale in Dongying formation

For the drilling operation in hard brittle shale formation, wellbore collapse occurs frequently, highly restricting the development of oil and gas. In order to reduce wellbore instability, in this paper, we use experiment to analyze the physical and chemical properties of hard brittle shale, conduct quantitative investigation on the influence of drilling fluid on shale. Based on the experiment results, elastic theory and single weak plane criterion have been used to establish wellbore stability model, which considers influences of weak plane, formation temperature and hydration. We conduct investigation on influence factors of wellbore stability. Its results show that The existence of weak plane cause increment of collapse pressure. In particular, the distribution of collapse pressure is variable with changing occurrence of weak plane. The monotone change pattern disappears due to weak plane. With increasing temperature difference, collapse pressure rises. However, its increment is relatively smaller. Drilling fluid impact will shrink safe well trajectory, boosting risk of wellbore collapsing. Finally, the application indicates that this model in the paper is able to precisely predict collapse pressure, offering reference for drilling in oilfield.