刚性颗粒封堵裂缝地层漏失机制数值模拟

Numerical simulation on the mechanism for rigid particle plugging of leakage in fracture formations

漏失裂缝封堵机理至今未得到全面地认识,以致于漏失裂缝封堵问题一直困扰着钻井工程界。为了提高对漏失裂缝堵漏的效率,基于CFD-DEM数值理论,利用Fluent-EDEM软件建立了漏失裂缝封堵模型,研究了堵漏颗粒粒径、浓度、粒度级配以及裂缝形态等参数对漏失裂缝封堵效率的影响规律,揭示了漏失裂缝封堵机理。研究结果表明:①“桥堵”效率是决定漏失裂缝封堵效率的根本因素,恰当地利用堵漏颗粒摩擦系数、尺寸及级配关系有助于提高漏失裂缝封堵效率,摩擦系数越大越有利于颗粒在漏失裂缝中形成桥堵,裂缝中弯折角会增加颗粒在漏失裂缝中搭桥的概率;②在一定程度上,漏失裂缝的弯曲度会影响堵漏颗粒在漏失裂缝中的运移特征及“桥堵效率”;③封堵漏失裂缝的堵漏颗粒浓度存在着一个“桥堵窗口”,低于“桥堵窗口”下限,堵漏颗粒不能在裂缝内形成有效的桥堵,而高于“桥堵窗口”上限则堵漏颗粒浓度对桥堵效率影响不大。结论认为,除了颗粒浓度和颗粒级配外,裂缝和颗粒特征参数对颗粒在漏失裂缝中建立高效桥堵的过程是不可忽略的影响因素。

So far,the plugging mechanism of leakage fractures has not been fully understood,so the plugging of leakage fractures has always been a difficulty in the circle of drilling engineering.In order to improve the plugging efficiency of leakage fracture,this paper establishes a leakage fracture plugging model by using the Fluent-EDEM software based on the CFD-DEM numerical theory.Then,the influence laws of plugging particle size,concentration and size distribution and fracture morphology on the plugging efficiency of leakage fractures are studied and the plugging mechanisms of leakage fractures are revealed.And the following research results are obtained.First,"bridging"efficiency is the fundamental factor to determine the plugging efficiency of leakage fractures.The proper use of the friction coefficient,size and size distribution of plugging particles is conducive to improving the plugging efficiency of leakage fractures.The higher the friction coefficient is,the easier it is for particles to form bridging in leakage fractures.The bending angle in fractures can increase the probability of particle bridging in leakage fractures.Second,to a certain extent,the curvature of leakage fractures can impact the migration characteristics and"bridging efficiency"of plugging materials in leakage fractures.Third,the concentration of the leakage fracture plugging particles has a"bridging window".Below the lower limit of the"bridging window",the plugging particles cannot form effective bridging in fractures;and above the upper limit,the plugging particles have little effect on bridging efficiency.In conclusion,besides particle concentration and particle size distribution,the characteristic parameters of fractures and plugging materials are the influence factors that shall not be neglected in the building process of efficient bridging from particles in leakage fractures.