The Dynamic Laws of Overflow Intrusion in Fractured Formations
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摘要: 在裂缝性地层钻井过程中，钻遇高压裂缝会出现比较严重的溢流，现有溢流机理模型多根据渗透性地层渗流理论建立，不适用于裂缝性地层，需要对自然条件下气体从裂缝流动至井筒的过程进行研究。分别基于赫兹弹性接触理论和二项式渗流理论，建立了裂缝微观闭合模型和裂缝气体流动模型，并以裂缝压力为结合点对两个模型进行了耦合，联立形成了考虑裂缝闭合条件的单条裂缝欠平衡溢流侵入模型。采用有限差分法对模型进行了数值求解，得到了考虑/不考虑闭合情况下裂缝几何形态（开度、半径）及压差对溢流规律的影响。模拟结果显示，相较于未考虑裂缝闭合情况的模型，由考虑裂缝闭合情况的模型得到的裂缝压降明显减缓，溢流持续时间变长，溢流速率变快，溢流总量更多。研究结果表明，相比于传统渗透性地层，裂缝性地层的溢流更加剧烈。Abstract: When a high pressure zone is encountered while drilling a fractured formation,a serious well kick will occur as overpressured formation fluids flow into the borehole.Most of the existing overflow mechanism models are based on the seepage theory of permeable formations,but they are snot applicable to fractured formations.Therefore,it is necessary to study the process of gas flowing into wellbore from the fractures under normal conditions.Based on the Hertz elastic contact theory and the binomial seepage theory,both the fracture microscopic closure model and the fracture gas flow model were established.The two models were coupled by taking the fracture pressure as the node.Then a single fracture underbalanced overflow intrusion model was established simultaneously by considering the fracture closure conditions.The finite difference method was used to find the numerical solution of the model.Then influences of fracture geometry(opening,radius)and pressure difference on the overflow laws were obtained under the conditions with/without considering the closure conditions.The simulation results showed that the fracture pressure drop clearly slowed down compared with the model without considering fracture closure,and in this case,the overflow duration lasted longer.So,the overflow rate increased,and the total volume of overflow was greater.The research results indicated that the overflow in fractured formations was more severe than that in conventional permeable formations.
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Keywords:
- fractured formation /
- drilling /
- overflow /
- fracture opening /
- intrusion law
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