异常高压致密油藏CO_(2)吞吐参数优化及微观孔隙动用特征--以准噶尔盆地吉木萨尔凹陷芦草沟组为例

Optimization of CO_(2) huff⁃puff parameters and micro⁃pore producing characteristics of the tight oil reservoirs with abnormal high pressure:Taking Lucaogou Formation in Junggar⁃Basin Jimsar Sag as an example

为改善吉木萨尔凹陷芦草沟组致密油藏在衰竭开发中产量递减快、采收率低的现象,提高储层动用程度,选取3种不同孔隙类型岩心,开展一系列CO_(2)吞吐岩心实验,在明确生产压力、吞吐次数和闷井时间对吞吐效果影响的基础上,引入核磁共振分析技术,定量评价了不同孔隙结构岩心中不同孔径孔隙的原油动用程度。研究表明:目标储层3类孔隙结构岩心的吞吐采收率随生产压力、吞吐次数和闷井时间的变化规律基本相似,最佳生产压力为21 MPa,最佳吞吐次数控制在5次以内,最佳闷井时间为12 h;吞吐过程中岩心孔隙结构差异会形成不同类型的动用特征,储层物性较好的岩心,大孔隙的原油采出程度始终高于小孔隙,是总采收率的主要“贡献者”,而储层物性差的岩心在吞吐初期大孔隙的原油采出程度高于小孔隙,但在后续吞吐中小孔隙的原油采出程度迅速增加,在累计吞吐采收率中占比达到53%以上。研究成果为吉木萨尔凹陷异常高压致密油藏顺利开展CO_(2)吞吐提供了重要依据。

In order to improve the phenomena of the rapid production decline,low recovery and high remained oil saturation in the depletion development of Lucaogou⁃Formation tight oil reservoirs in Jimsar Sag,and moreover to enhance the developed degree of the reservoir,three different pore types of the cores were selected.Through a se⁃ries of the core experiments of CO_(2)huff and puff,on the basis of clarifying the influences of the production pres⁃sure,huff⁃puff times and soak time on the huff and puff effects,with the help of the introduced nuclear magnetic resonance(NMR)analyzing technique,the crude⁃oil developed characteristics in different⁃pore⁃structure cores with different sizes were quantitatively evaluated.The study results show that the varied laws of the recovery with the production pressure,huff⁃puff times and soak time of three different⁃type cores are generally similar,the optimal production pressure is 21 MPa,the optimal huff and puff times are controlled within 5 times,and the optimal soak time is 12 h.In the process of the huff and puff,the difference of the pore structure can form different types of the production characteristics,for the cores with much better physical properties,the oil recovery degree of the macro⁃pore is always higher than that of the small one,the former is the main“contributor”of the total recovery.Howev⁃er,for the core with poorer physical properties,although in the initial stage,the oil recovery degree of the large pores is as the same as that of the much better core,the recovery degree increases rapidly in the subsequent huff and puff,which accounts for more than 53%of the accumulative huff⁃puff recovery.The research results have pro⁃vided the evidences for the smooth operation of the CO_(2)huff and puff in the abnormal high⁃pressure tight oil reser⁃voirs of Jimsar Sag.