Micropore structure and movable fluid distribution characteristics of tight sandstone reservoirs: Taking the He 8 reservoir in the Shenmu area of the eastern Ordos Basin as an example
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摘要:
致密砂岩复杂的孔喉结构导致多变的可动流体分布, 而微观孔隙结构和可动流体分布又是研究致密砂岩储层的重点。基于核磁共振可动流体测试原理, 采用离心试验、高压压汞、扫描电镜、X射线衍射及铸体薄片等方法, 建立了神木地区盒8段储层孔隙结构分类标准, 明确了3类岩石孔隙结构参数及孔隙、喉道类型, 提出了适用于目标储层转换系数的新方法, 并定量评价了3类岩石可动流体分布特征。研究结果表明, 目标储层中Ⅰ、Ⅱ类岩石孔隙以孔径大于10 μm的残余粒间孔和孔径大于1 μm的溶蚀孔为主, 喉道以缩小型和弯片状喉道为主, 孔隙结构参数较好, 大孔隙发育程度高、孔喉间连通性好、可动流体赋存量大, 大部分可动流体赋存于
T 2谱右峰对应的大孔隙中, 而左峰对应的小孔隙中可动流体含量低。Ⅲ类岩石孔隙结构参数差、可动流体百分比低、孔喉以晶间孔和管束状喉道为主。目标储层平均转换系数为0.029 μm/ms, 但Ⅰ、Ⅱ类岩石转换系数小于Ⅲ类, 转换后的Ⅰ、Ⅱ类岩石T 2谱的右峰与压汞孔隙半径分布的主峰相对应, 而Ⅲ类岩石T 2谱的左峰与压汞孔隙半径分布的主峰相对应。Ⅰ、Ⅱ类岩石孔径大于1 μm的孔隙中可动流体百分比高, 是未来勘探开发的主要方向。研究成果为提高致密油藏采收率提供了参考和借鉴。Abstract:Objective The complex pore throat structure of tight sandstone leads to variable distribution of movable fluid, and the micropore structure and distribution characteristics of movable fluid are the focus of the study of tight sandstone reservoirs.
Methods Based on the principle of the nuclear magnetic resonance (NMR) movable fluid test, the classification standard of pore structure of the He 8 reservoir in the Shenmu area was established using centrifugal test, high-pressure mercury injection, scanning electron microscope, X-ray diffraction and casting thin section. The pore structure parameters and pore throat types of the three types of rocks are defined, and a new method for measuring the conversion coefficient suitable for tight sandstone reservoirs was proposed. The distribution characteristics of movable fluid of three types of rocks were also quantitatively evaluated.
Results The results reveal that the type Ⅰ and Ⅱ rock pores in the target reservoir are mainly residual intergranular pores with pore diameters greater than 10 μm and dissolution pores with pore diameters greater than 1 μm. The throats are mainly reduced and curved flaky throats, with good pore structure parameters, a high development degree of large pore space, good connectivity between pore throats, and a large amount of movable fluid.Most of the movable fluid occurs in the macropores corresponding to the right peak of the
T 2 spectrum, while the content of the movable fluid in the small pores corresponding to the left peak is low. The pore structure parameters of type Ⅲ rocks are poor, the percentage of movable fluid is low, and the pore throats are mainly intergranular pores and tube bundle throats. The average conversion coefficient of the target reservoir is 0.029 μm/ms, but the conversion coefficients of type Ⅰ and Ⅱ rocks are less than that of type Ⅲ rocks. The right peak of theT 2 spectrum of type Ⅰ and Ⅱ rocks after conversion corresponds to the main peak of the mercury porosimetry pore radius distribution, while the left peak of theT 2 spectrum of type Ⅲ rocks corresponds to the main peak of the distribution of mercury porosimetry pore radius. The percentage of movable fluid in the pores of type Ⅰ and type Ⅱ rocks with pore diameters greater than 1 μm is high, which is the main direction of exploration and development in the future.Conclusion The results provide a reference for improving the recovery of tight reservoirs.
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表 1 6块岩心不同离心力离心前后含水饱和度变化
Table 1. Changes in the water saturation of 6 cores before and after centrifugation with different centrifugal forces
样品数 施加[0.69, 2.09) MPa离心力 施加[2.09, 2.76) MPa离心力 施加[2.76, 4.14] MPa离心力 含水饱和度减少量/% 平均减少量/% 含水饱和度减少量/% 平均减少量/% 含水饱和度减少量/% 平均减少量/% 6 22.14~34.27 19.28 4.31~11.28 7.17 0.66~1.13 0.81 表 2 实验岩心基本物性参数及转换系数
Table 2. Basic physical parameters and conversion coefficient of the experimental core
储层类型 岩心编号 储层物性 可动流体参数 压汞参数 最佳离心力下孔隙动用下限对应T2值/ms 压汞与NMR之间转换系数/(μm·ms-1) 孔隙度/% 渗透率/10-3μm2 可动流体百分比/% 可动流体孔隙度/% 阈值压力/MPa 中值压力/MPa 中值半径/μm 平均孔喉半径/μm 分选系数 最大进汞饱和度/% Ⅰ类 1 9.82 0.086 56.25 5.51 0.97 6.66 0.177 0.258 2.68 93.52 2.28 0.023 2 6.43 0.045 48.07 3.09 1.55 10.27 0.145 0.495 1.85 94.65 2.76 0.019 3 8.81 0.076 54.66 4.82 2.24 5.06 0.160 0.210 2.81 72.56 2.82 0.019 4 6.35 0.067 38.75 2.46 3.96 12.31 0.066 0.117 2.86 68.99 1.98 0.027 5 9.42 0.206 63.30 5.95 0.81 2.71 0.299 0.482 2.27 100.00 3.17 0.017 平均 8.17 0.096 52.21 4.37 1.91 7.40 0.170 0.310 2.49 85.94 2.60 0.021 Ⅱ类 6 9.01 0.150 59.30 5.34 0.43 10.26 0.118 0.194 2.12 71.78 1.68 0.032 7 6.89 0.082 40.59 2.80 0.51 5.97 0.135 0.282 3.51 99.45 3.53 0.015 8 7.64 0.036 37.47 2.86 4.88 9.40 0.086 0.102 2.27 72.68 3.88 0.014 9 7.25 0.020 28.34 2.05 6.30 18.38 0.044 0.059 3.06 73.9 4.26 0.012 10 10.68 0.127 43.31 4.63 0.91 4.58 0.237 0.400 3.08 90.56 4.68 0.011 平均 8.29 0.083 41.80 3.54 2.61 9.72 0.120 0.210 2.81 81.67 3.61 0.017 Ⅲ类 11 5.78 0.007 17.57 1.01 13.11 79.73 0.011 0.046 3.52 70.05 1.13 0.047 12 5.11 0.005 26.63 1.36 21.90 137.76 0.006 0.034 3.25 52.20 1.08 0.049 13 9.06 0.014 23.01 2.08 3.22 21.23 0.038 0.043 4.06 80.79 0.84 0.063 14 9.69 0.030 14.75 1.43 2.05 18.66 0.043 0.116 3.69 98.90 1.32 0.040 15 7.16 0.014 11.54 0.83 1.67 42.57 0.019 0.207 2.42 94.31 0.96 0.055 平均 7.36 0.014 18.70 1.34 8.39 59.99 0.020 0.090 3.39 79.25 1.07 0.051 -
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