Experimental study on the mobility of Junggar Basin's Jimsar shale oil by CO2 huff and puff under different temperatures and pressures
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摘要: 准噶尔盆地吉木萨尔页岩油储集层主要发育微纳尺度孔喉裂隙系统,同时油质黏稠,动用难度大,注CO2吞吐是提高采收率的重要技术。为了认清吉木萨尔页岩油储层注CO2吞吐下的可动性规律,对该区芦草沟组45块岩心进行了研究。储层岩性为云屑砂岩、砂屑云岩和岩屑砂岩;储层覆压孔隙度介于2.0%~22.7%之间,平均为11%,覆压渗透率平均为0.01×10-3 μm2,小于0.1×10-3 μm2的样品占比达90%以上。根据岩心物性分类,选取20块岩样开展核磁实验,对页岩油低场核磁共振实验测量的6个关建参数进行了优化;通过将页岩油压汞实验数据和低场核磁共振实验数据对比,在对数坐标下建立了页岩岩心的T2值与孔隙半径之间的线性关系,通过T2谱定量获得了页岩的孔隙半径分布。在此基础上,在不同温压条件下开展9种CO2吞吐实验,结合采收率、动用程度等指标分析得知,半径小于300 nm的小孔隙中页岩油难以动用,300~1 000 nm的中孔隙和大于1 000 nm的大孔隙中页岩油动用程度相对较高,且随着温度和压力的提高而增大。Abstract: Micro- and nano-scale pore-throat fissure systems were mainly developed in the Jimsar shale oil reservoir of the Junggar Basin with the oil of viscous and difficult to be produced.CO2 huff-and-puff is an important technology to enhance the oil recovery. To understand the mobility law of Jimsar shale oil reservoir under CO2 huff and puff, 45 cores of the Lucaogou Formation in this area were studied in this study.The cores was classified into dolomitic sandstone, doloarenite and lithic sandstone. The overburden porosity of the reservoir is 2.0%-22.7%, and the average value is only 11.0%. The average overburden permeability is 0.01×10-3 μm2, and more than 90% of the samples have permeability lower than 0.1×10-3 μm2. According to physical property classification, 20 rock samples were further selected and 6 key parameters for low-field NMR measurement were optimized. By comparing the experimental data of shale oil mercury injection with those of low-field NMR, the linear relationship between T2 value and pore radius of shale core was established in logarithmic coordinates.The pore radius distribution of shale was obtained quantitatively according to the T2 spectrum. 9 kinds of CO2 huff and puff experiments were carried out under different temperatures and pressures. The analyses of recovery rate, utilization degree and other indicators show that shale oil in small pores(r < 300 nm) is difficult to produce, and the utilization degree of shale oil in medium pores (300 nm < r < 1 000 nm) and large pores(r>1 000 nm) is relatively higher, and increases with the increase of temperature and pressure.
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Key words:
- low-field NMR /
- CO2 huff and puff /
- mobility /
- shale oil /
- Jimsar Sag /
- Junggar Basin
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表 1 准噶尔盆地吉木萨尔页岩油岩心物性统计分析
Table 1. Physical property of Jimsar shale oil cores in Junggar Basin
序号 岩性 孔隙度/% 渗透率/10-3 μm2 序号 岩性 孔隙度/% 渗透率/10-3 μm2 1 砂屑云岩 9.7 0.011 24 云屑砂岩 20.8 0.486 2 砂屑云岩 7.9 0.016 25 云屑砂岩 22.7 0.594 3 砂屑云岩 14.0 0.282 26 云屑砂岩 10.2 0.007 4 砂屑云岩 9.0 0.014 27 云屑砂岩 11.0 0.045 5 砂屑云岩 17.3 0.712 28 云屑砂岩 7.5 0.947 6 砂屑云岩 9.7 0.016 29 云屑砂岩 2.0 0.012 7 砂屑云岩 11.8 0.093 30 云屑砂岩 14.3 0.023 8 砂屑云岩 11.7 0.045 31 云屑砂岩 9.9 0.016 9 砂屑云岩 15.4 0.041 32 云屑砂岩 9.1 0.020 10 砂屑云岩 7.2 0.028 33 云屑砂岩 7.1 0.028 11 砂屑云岩 2.5 0.154 34 云屑砂岩 7.0 0.015 12 砂屑云岩 9.2 0.020 35 砂屑云岩 10.8 0.402 13 砂屑云岩 10.2 0.056 36 云屑砂岩 9.3 0.017 14 砂屑云岩 4.7 0.031 37 岩屑砂岩 12.9 0.149 15 砂屑云岩 7.7 0.016 38 岩屑砂岩 14.5 0.250 16 砂屑云岩 8.0 0.013 39 岩屑砂岩 15.0 0.234 17 砂屑云岩 4.9 0.015 40 岩屑砂岩 11.8 0.057 18 砂屑云岩 4.9 0.014 41 岩屑砂岩 15.2 0.298 19 砂屑云岩 6.8 0.018 42 岩屑砂岩 16.1 0.298 20 砂屑云岩 13.0 0.018 43 岩屑砂岩 16.0 0.565 21 云屑砂岩 13.9 0.023 44 岩屑砂岩 17.1 0.157 22 砂屑云岩 16.0 0.065 45 岩屑砂岩 16.0 0.991 23 砂屑云岩 16.5 0.089 表 2 准噶尔盆地吉木萨尔页岩油岩心核磁共振实验测量参数优化
Table 2. Parameter optimization of NMR experiment for Jimsar shale oil cores in Junggar Basin
参数 数值 优化原则 Tau值 70 μs 为了防止机器过热,扫描次数大于2 000时,适当增加Tau值,一般大于70 μs 回波数目 1 500 回波数目×2Tau≈3T1 扫描次数 3 500 保证信噪比>100 等待时间 200 ms 3T1~5T1 相位循环 8 保证信噪比>100 回波点数 1 增加回波点数可观察弛豫信号细节,一般为1 表 3 不同温压条件下准噶尔盆地吉木萨尔页岩油岩心CO2吞吐实验方案
Table 3. Experimental scheme of CO2 huff-and-puff in Jimsar shale oil cores of Junggar Basin under different temperatures and pressures
实验类别 岩心物性及实验条件 孔隙度/% 渗透率/10-3μm2 小圆柱尺寸(D×L)/mm 岩性 温度/℃ 压力/MPa 同岩性同温不同压 7.92 0.028 25.30×68.76 云屑砂岩 50 5 9.03 0.020 25.46×49.02 云屑砂岩 50 10 7.16 0.023 25.70×61.58 云屑砂岩 50 15 5.67 0.018 25.46×46.12 云屑砂岩 50 20 同岩性同压不同温 7.67 0.030 25.70×41.20 云屑砂岩 30 10 5.94 0.031 25.56×52.14 云屑砂岩 70 10 7.50 0.023 25.02×70.10 云屑砂岩 90 10 同温同压不同岩性 14.50 0.250 25.14×60.30 砂屑云岩 50 10 11.40 0.038 25.18×67.00 岩屑砂岩 50 10 -
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