页岩气多裂缝通道中的沉降特性研究

The Study on the Transport and Deposition Characteristics of Shale Gas in Multi-fracture Channels

水力压裂是页岩气增产的核心技术,使页岩气流形成高导流能力的裂缝通道,支撑剂在裂缝中沉积并形成具有较好流通性能的砂堤,这对页岩气高效开采具有重要的影响。针对压裂液中支撑剂在多裂缝通道中的输送特性展开分析研究。在一定假设基础上建立起简化的多通道裂缝模型,采用欧拉-拉格朗日两相流数值仿真方法对支撑剂在裂缝内的输送分布规律进行了计算分析,讨论了支撑剂密度和粒径改变时对支撑剂在不同截面上浓度、速度分布以及携砂率的影响。计算结果表明,水平井段内支撑剂密度越高,粒径越大,井中下部沉积的数量越多,水平方向平均速度越小;支撑剂密度越高,粒径越大,水平井段内携砂率逐渐减小。不同支撑剂密度条件下,下游裂缝出口沿缝宽方向颗粒浓度分布比上游均匀。在不同支撑剂粒径条件下,小颗粒在下游裂缝出口沿缝宽方向颗粒浓度分布比上游均匀,而大颗粒表现则相反;在裂缝通道内,支撑剂密度越低,粒径越小,沿缝宽方向分布越均匀,垂直方向平均速度越小。研究结果可为工程实际中支撑剂的选取提供科学依据。

Hydraulic fracturing is the main technology to increase the production of shale gas, whose purpose is to form fracture channels with high diversion ability. Both deposition characteristics of proppant in fractures and the for- mation of sand embankment have an important impact on the efficient exploitation of shale gas. Thus this paper in- tends to analyze the transport properties of proppant in fractures. Based on reasonable hypothesis, this article estab- lished a simplified multi-fracture model, employed Euler-Lagrange two-phase numerical method to study the trans- port distribution of proppant in fractures and discussed the influence of changes of proppant density and diameter on distribution characteristics of velocity and concentration at different sections. The results show that with the increase of proppant density and diameter, the deposition number at the bottom of wells rises and the horizontal average veloci- ty decreases in horizontal sections; The larger the proppant density and diameter, the greater the cutting-carrying a- bility in horizontal sections; In fracture channels at the conditions of different proppant densities, the.c^ncentrati^n distribution of particles in downstream outlets is more uniform along the width than in upstream. Under the conditions of different proppant diameters, the concentration distribution of small particles in downstream outlets is more uniform along the width than the upstream, however, the condition is contrary for big particles; In multi-fracture channels, with the decrease of proppant density and diameter, particles distribute more uniformly along the width and the verti- cal average flow rate decreases. The results provide a scientific basis for engineering to select proppant.