针对致密油藏水平井自然渗吸采收率低和长期衰竭开发后期地层能量如何补充的难题,在储层基本特征、致密油藏注水吞吐采油机理的基础上,提出了大排量水平井注水吞吐.以鄂尔多斯盆地长7段致密油藏为研究对象,选取天然岩心和人造岩心相结合方式,利用核磁共振等方法,通过室内注水吞吐实验研究了自然渗吸和不同注水速度下吞吐动态渗吸的作用范围和微观孔隙动用特征,分析了排量对孔隙动用情况的影响,并开展了焖井时间影响实验,最后利用数值模拟方法对压裂水平井注水吞吐开发的注水量、焖井时间参数进行优化.研究表明:小排量时,注水吞吐主要动用的是大孔隙,中小孔隙动用较低;大排量时,注水吞吐不仅动用了大孔隙,且中小孔隙动用明显提高,使得整体的采收率出现较大增加.随着焖井时间的延长,油水置换作用越充分,使得注水吞吐采出程度越高,但其提高的程度逐渐稳定.对A9井进行数值模拟优化,得到最佳日注水量为900 m3,最佳焖井时间为24 d,在矿场试验取得成功,初期日增油2.11 t,有效期365 d,累计增油770 t.
Huff-n-puff technology and parameter optimization of large displacement water injection in tight oil reservoir
To address the issue of low natural imbibition recovery in horizontal wells within tight reservoirs and the challenge of replenishing formation energy during extended depletion phases,a strategy involving water injection huff and puff in large displacement horizontal wells was proposed.This approach builds on the fundamental characteristics of reservoirs and the established mechanisms of water injection huff and puff oil production in tight reservoirs.The research focused on the Chang-7 tight reservoir in Ordos Basin,employing a combination of natural and artificial cores.This study explored the range of natural imbibition and the dynamics of water injection and huff and puff across various displacements.Methods like nuclear magnetic resonance were used to analyze the characteristics of microscopic pore production,the impact of displacement on pore productivity,and the effects of soaking time.The findings reveal that with smaller displacements,mainly large pores are utilized for water injection,resulting in minimal engagement of small and medium pores.Conversely,higher water injections significantly enhance the involvement of small and medium-sized pores,thus substantially boosting the overall recovery rate.Additionally,as the simmering time is extended,the oil-water displacement effect increases,enhancing the degree of recovery through water injection huff and puff,though the rate of improvement eventually stabilizes.Numerical simulation was used to optimize the parameters for water injection huff and puff development in fracturing horizontal wells.For Well-A9,the optimal parameters were identified as a daily water injection rate of 900 m3 and a simmering time of 24 days.The field test confirmed the effectiveness of these parameters,with an initial daily oil increase of 2.11 tons,an effective period of 365 days,and a cumulative oil increase of 770 tons.
large displacement water injectiontight oil reservoirhorizontal wellnuclear magnetic resonancenumerical simulation
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