深层低渗透砂砾岩油藏注CO_(2)吞吐提高采收率实验研究

Experimental Study on Enhanced Oil Recovery by CO_(2) Huff and Puff in Deep Low Permeability Glutenite Reservoir

深层低渗透砂砾岩油藏地层天然能量较低,压裂后产能递减较快,并且由于地层水敏性以及非均质性较强,采取注水开发的效果较差,采出程度较低。为进一步提高此类油藏的开发效率,开展了注CO_(2)吞吐提高采收率实验研究,分析了生产压力、焖井时间、吞吐周期以及岩心渗透率对吞吐采收率的影响,并结合核磁共振分析实验研究了CO_(2)吞吐微观孔隙动用特征。结果表明:生产压力越低、焖井时间越长,吞吐采收率越高;随着吞吐周期的增加,周期吞吐采收率和换油率均逐渐降低;岩心的渗透率越大,不同周期的吞吐采收率就越高;注CO_(2)吞吐的最佳生产压力为26 MPa,最佳焖井时间为8 h,最佳吞吐周期为5次。岩心的孔隙结构对CO_(2)吞吐过程中原油的微观动用特征影响较为明显,大孔隙发育较少、物性较差的岩心,吞吐初期主要动用大孔隙中的原油,而吞吐后期采收率的贡献主要来自小孔隙,此类岩心整体采出程度较低;而对于大孔隙发育较多、物性较好的岩心,大孔隙中原油的动用程度一直高于小孔隙,并且总体采出程度较高。S-1Y井实施注CO_(2)吞吐措施后,日产油量明显提升,含水率明显降低,取得了较好的增油效果。

The formation natural energy of deep low permeability glutenite reservoir is relatively low,and the productivity decreases rapidly after fracturing.Moreover,due to the strong formation water sensitivity and heterogeneity,the effect of water injection development is poor and the recovery degree is low.In order to further improve the development efficiency of this kind of reservoir,the experimental research on enhanced oil recovery by CO_(2)huff and puff was carried out.The effects of production pressure,soak time,huff and puff cycle and core permeability on huff and puff recovery were analyzed.Combined with NMR analysis experiment,the micro pore production characteristics of CO_(2)huff and puff were studied.The results show that the lower the production pressure and the longer the soak time,the higher the recovery efficiency of huff and puff.With the increase of huff and puff cycle,the recovery and oil change efficiency of cyclic huff and puff gradually decrease.The higher the permeability of the core,the higher the recovery of huff and puff in different cycles.The optimal production pressure of CO_(2)injection huff and puff is 26 MPa,the optimal soak time is 8 h,and the optimal huff and puff cycle is 5 times.The pore structure of the core has obvious influence on the micro production characteristics of crude oil during CO_(2)huff and puff,for the cores with less macro-pores and poor physical properties,the crude oil in macro-pores is mainly used in the initial stage of huff and puff,while the contribution of recovery factor in the later stage of huff and puff mainly comes from small pores,and the overall recovery degree of such cores is low.For the cores with more macro-pores and better physical properties,the production degree of crude oil in macro-pores is always higher than that in small pores,and the overall recovery degree is high.After the implementation of CO_(2)injection huff and puff measures in S-1Y well,the daily oil production has been significantly increased,the water cut has been significantly reduced,and a good oil increasing effect has been achieved.