水平井多裂缝尖端应力干扰现象分析

Analysis of Stress Interference Phenomenon in Multi-fracture Tips of Horizontal Well

致密砂岩储层具有低孔低渗的特征,水平井多裂缝压裂是致密砂岩储层油气增产的重要手段,合理预测裂缝扩展趋势是进行水力压裂开采的关键.为了准确认识水平井多裂缝压裂过程中尖端应力场变化,综合考虑地应力分布、井筒内压等因素,建立二维均质流固耦合有限元数值分析模型.模拟了致密砂岩储层不同裂缝半长、不同裂缝条数、不同裂缝间距及不同裂缝位置的应力场,进一步分析裂缝尖端应力干扰情况.结果表明,裂缝尖端附近存在明显的应力干扰现象,多裂缝同时压裂时,裂缝半长越长,裂缝条数越多,裂缝间距越小,应力干扰现象越明显.中间位置裂缝应力受附近裂缝的应力干扰,裂缝尖端应力集中值明显降低,不利于裂缝延伸和扩展,两侧裂缝尖端的应力集中有所增加.该研究深入认识水平井多裂缝压裂裂缝起裂和延伸机制,对制定压裂方案具有一定的指导意义.

Tight sandstone reservoirs have the characteristics of low porosity and low permeability.Multi-fracture in horizontal wells is an important way to increase oil and gas production in tight sandstone reservoirs.Reasonable prediction of fracture initiation and propagation is the key to the design of hydraulic fracturing.In order to understand the variation of tip stress field in multi-fracture fracturing process of horizontal wells accurately,a two-dimensional homogeneous fluid-solid coupled finite element numerical analysis model was established with considering comprehensive factors such as in-stiu stress distribution and wellbore internal pressure.The stress fields of different fracture lengths,number of fractures,spacing of fractures and location of fractures in tight sandstone reservoirs were simulated,and the stress interference at fracture tip was analyzed.The results show that there is an obvious stress interference phenomenon near the crack tip.When multiple fractures initiate and propagate simultaneously,the longer the half-length of fractures,the more the number of fractures,the smaller the spacing between the fractures,and the more obvious the stress interference phenomenon is.Due to the stress interference of nearby fractures,the stress value of the fracture tip in the middle position is reduced obviously,which is not conducive to the propagation of fractures,and the stress concentration at the fracture tips on both sides is increased.The initiation and propagation mechanism of multi-fracture in horizontal wells was deeply studied in this paper,which is of certain guiding significance for the design of hydraulic fracture.