APPLICATION OF PRESTACK INVERSION METHOD IN THE PREDICTION OF TIGHT SANDSTONE GAS RESERVOIR
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摘要: 以鄂尔多斯东缘A区块为例,通过岩石物理正演分析,论证了储层岩石物理参数的敏感性,确定利用纵波阻抗与纵横波速度比参数进行储层的识别。在此基础上进行正演模拟,研究了地震的极限分辨率及不同厚度砂体的地震响应特征,确定了运用叠前地质统计学反演为核心的储层预测技术对该研究区太原组进行储层预测研究,以解决该区储层薄、横向变化快、单一岩石物理参数无法区分岩性等问题。地质统计学反演结果表明,该方法能有效的预测厚度大于3 m的储层。对比研究区内11口测井解释厚度与储层反演厚度表明,储层反演预测厚度平均误差为7.5%,其中5口盲井的平均误差为10.2%,一口新钻井的砂体厚度预测误差为1.73%,为该区的井位部署提供了可靠的资料参考。Abstract: Taking A block of eastern Ordos Basin as an example, reservoir petrophysical sensitive parameters are demonstrated though the work of petrophysical analysis which shows that the single impedance parameter can't be applied to identify the reservoir and the parameter Vp/Vs must be used for the identification. Though the analysis of seismic simulation, the seismic resolution and the seismic-response characteristics of different sand thicknesses are studied. Based on the study of seismic simulation, in order to solve the problems of tiny thickness reservoir, rapid lateral variation and reservoir recognition difficulty, the pre-stack geostatistical inversion is chosen as the research method. Comparison of the thickness of well log interpretation and reservoir inversion in 11 wells shows that pre-stack geostatistical inversion can effectively identify reservoir with thickness more than 3m. The results of inversion are considered achieving a high accuracy prediction of reservoir with a thickness average error rate of 7.5%, the average error of five blind wells is 10.2% and the new well is 1.73% which provides a strong reference for well placement.
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表 1 正演模型参数表
Table 1. Forward model parameters
编号 厚度/m 纵波阻抗/g·cm-3·m·s-1 纵横波速度比 密度/g·cm-3 1号砂体 3.2 10220 1.71 2.52 2号砂体 12 9855 1.69 2.50 3号砂体 4.1 10060 1.70 2.51 泥岩 12600 1.90 2.69 表 2 研究区太原组各岩性弹性参数X、Y、Z方向变程
Table 2. X/Y/Z direction variable range of different lithologies of Taiyuan formation
岩性 X/m Y/m Z/ms 砂岩 1200 1200 1 泥岩 1600 1600 2 煤 1000 1000 4 表 3 A-6井太原组砂体预测精度对比
Table 3. Sand body prediction accuracy comparison in Taiyuan formation of A-6 well
砂体编号 测井厚度/m 反演厚度/m 误差/% 备注 1 4.26 3.2 24.8 含0.4 m泥岩夹层 2 2.2 0 3 5.0 4.3 14 4 2.8 0 5 1.4 0 6 1.3 0 7 5.0 5.6 12 含0.1 m泥岩夹层 8 1.5 0 9 1.5 0 表 4 叠前地质统计学反演误差统计表
Table 4. Error statistics of pre-stack geostatistical inversion
井名 层位 钻井砂厚/m 预测砂厚/m 误差率/% A-4 T2 23.20 21.66 6.64 A-5 T2 6.40 6.37 0.50 A-6 T2 15.00 14.85 1.02 A-8 T2 3.80 4.86 27.95 A-15 T2 4.10 4.31 5.18 A-16 T2 3.40 3.11 8.50 A-20 T2 20.70 20.40 1.46 A-26 T2 9.90 9.81 0.94 A-28 T2 24.00 22.46 6.40 A-101 T2 22.40 22.01 1.73 A-105 T2 13.40 15.45 15.29 误差均值: 7.5 注:A-8、A-15、A-26、A-101、A-105井均未参与反演约束 -
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