应力干扰下煤层顶板水平井穿层分段压裂规律

穿层压裂是提高煤层顶板水平井产气量的关键技术,而应力干扰对煤层顶板水平井穿层分段压裂效果具有重要影响,为此,建立顶板水平井穿层分段压裂数值模型,研究应力干扰对穿层分段压裂裂缝扩展的影响规律。结果表明:煤层的岩石力学参数、压裂段间距和压裂施工方式是影响顶板水平井穿层压裂段间干扰的3个重要因素,随着煤层泊松比的降低,叠加应力逐渐增加,段间干扰程度增加;随着段间距离的增加,叠加应力逐渐减少、应力干扰逐渐减弱;顶板岩层内的叠加应力和应力干扰程度明显大于煤层;渗流扩散泄压施工产生的叠加应力明显低于连续压裂施工,段间干扰程度明显降低。研究得出连续施工的中硬煤层分段间距在90 m左右,软煤层分段间距在70~80 m较合理。扩散泄压压裂施工段间距相应降低,中硬煤层的分段间距在70 m左右、软煤层分段间距在60 m左右较合理。工程实践表明,顶板水平井分段压裂裂缝穿透了煤层,形成了较长裂缝,取得了较好的产气效果,实现对煤层的高效穿层压裂改造,研究结果为顶板水平井穿层压裂段间距优化提供了理论依据。

Layer-penetrating staged fracturing law of horizontal wells within roof of coal seams under stress interference

Layer-penetrating fracturing is the key link to improve production in horizontal well within roof, and stress interference has important influence on layer-penetrating segmental fracturing effect in the horizontal well within roof. Therefore, the layer-penetrating segmental fracturing numerical model of horizontal well within roof is set up, the influence law of fracture propagation on stress interference to layer-penetrating segmental fracturing is studied. The results show that:the rock mechanics parameters, the interval distance and the fracturing construction method are the three important factors affecting the intersegment disturbance of the horizontal well within roof. As the Poisson's ratio of the coal seam goes down, the superposition horizontal stress increases gradually and the intersegment disturbance degree increases. With the increase of the interval distance, the superimposed horizontal stress gradually decreases and the stress interference gradually weakens. The superposition stress in roof strata is obviously greater than that in coal seam, and the interference degree of stress in roof strata is stronger than that in coal seam. The superposition horizontal stress produced by seepage diffusion pressure relief fracturing is obviously lower than that of continuous fracturing, and the interference degree between sections is obviously reduced. The results show that it is reasonable to keep the interval about 90 m in the medium hard coal seam under continuous construction, the interval of soft coal seam is reasonable about 70~80 m. The interval by seepage diffusion pressure relief fracturing is reduced correspondingly, and the interval between the medium hard coal seams is reasonable at about 70 m. The interval of soft coal seam is reasonable about 60 m. The engineering practice shows that the fractures of fracturing penetrate the coal seam and form relatively longer fractures in horizontal well within roof, thus achieving better gas production effect and achieving the goal of efficient layer-penetrating segmental fracturing for horizontal well within roof. The research results provide theoretical basis for the research on segmental interval optimization of horizontal well within roof.