裂缝性页岩气储层三维多簇水力裂缝竞争扩展数值模拟

NUMERICAL SIMULATION OF 3D MULTI-CLUSTER HYDRAULIC FRACTURE COMPETITIVE PROPAGATION IN FRACTURED SHALE GAS RESERVOIR

页岩气水平井多簇水力裂缝延伸效率是影响压裂效果的关键,现场监测发现大量射孔簇无法进液、多簇非均匀起裂扩展问题突出,深入认识三维空间中天然裂缝对多簇水力裂缝竞争扩展的影响规律具有重要意义。为此,基于离散格子方法建立三维全耦合随机裂缝性页岩储层三簇压裂数值模型,精细刻画多簇水力裂缝竞争起裂、扩展以及天然裂缝相互作用的全过程演化规律,研究地应力差、簇间距、压裂液黏度及排量等参数影响下多簇水力裂缝扩展行为,提出多簇延伸效率的施工对策。结果表明:水力裂缝与天然裂缝相遇时表现为穿透、转向、分叉等单一或多种复合模式;天然裂缝网络会加剧多簇裂缝竞争扩展时的应力阴影效应,中间受到抑制的射孔簇容易沿天然裂缝转向或者分叉并与其他射孔簇发生融合,降低整体改造面积;地应力差越小、簇间距越小,缝间应力干扰越明显,裂缝延伸规模越小;增大压裂液黏度或排量,中间簇水力裂缝受应力干扰程度减弱,延伸距离更远,建议现场在前置液阶段适当提高压裂液黏度、在主压裂阶段增大排量,以提高多簇水力裂缝的延伸效率。研究成果可为页岩气储层射孔分段以及压裂参数优化设计提供指导。

The extension efficiency of multi-cluster hydraulic fractures is key to the fracturing effect of shale gas horizontal wells.Field monitoring has found that many perforating clusters fail to feed fluid,and issues with non-uniform initiation and propagation of multi-cluster fractures are prominent.It is crucial to deeply understand the influence of the natural fractures'spatial distribution on the competitive expansion of multi-cluster hydraulic fractures.Therefore,a three-dimensional fully coupled numerical model for three-cluster fracturing in randomly fractured shale reservoirs is established based on the discrete lattice method.This model accurately describes the entire process and evolution of multi-cluster hydraulic fracture competition,propagation,and interaction with natural fractures.The study investigates the behavior of multi-cluster hydraulic fracture propagation under the influence of in-situ stress differences,cluster spacing,fracturing fluid viscosity,and injection rate.Construction measures to enhance the efficiency of multi-cluster extension are proposed.The results indicate that when hydraulic fractures encounter natural fractures,they exhibit single or multiple composite modes such as penetration,turning,and bifurcation.The natural fracture network intensifies the stress shadow effect during the competitive expansion of multiple fracture clusters,causing inhibited perforating clusters to easily turn or bifurcate along natural fractures and fuse with other perforating clusters,thereby reducing the fracture extension scale.The smaller the stress difference and cluster spacing,the more pronounced the stress interference between fractures and the smaller the fracture extension scale.Increasing fracturing fluid viscosity or injection rate reduces the degree of stress disturbance of intermediate cluster hydraulic fractures,resulting in longer extension distances.It is recommended to increase fracturing fluid viscosity appropriately during the pre-fluid stage and displacement during the main fracturing stage to improve the extension efficiency of multi-cluster hydraulic fractures.The research findings can guide the segmentation of shale gas reservoir perforations and the optimization of fracturing parameters.