An improved LSTM-based shear wave prediction method: A case study of fracture-cavity reservoirs in Tahe Oilfield
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摘要:
横波速度是表征岩土介质物理、力学性质的关键参数,在油气勘探开发中作用突出。碳酸盐岩缝洞储层结构复杂、非均质性极强,传统岩石物理模型与经验公式预测横波速度精度偏低。以塔河油田超深层缝洞储层为研究对象,提出基于降维技术与储集体类型划分的长短期记忆神经网络(long short-term memory,简称LSTM)横波速度方法先校正失真测井曲线,采用主成分分析法(principal components analysis,简称PCA)将声波时差、密度测井以及中子测井等11项测井参数降维为 5 个主成分;结合成像测井与电性特征,利用支持向量机(support vector machine,简称SVM)将储层划分为溶孔、裂缝、基岩、未充填溶洞、充填砂泥质溶洞、充填角砾溶洞6类,再构建LSTM深度学习模型开展分类型横波速度预测。结果表明,本方法对缝洞储层的横波预测精度达到91%,相对于传统经验公式具备显著提升。本研究提出的 PCA-SVM-LSTM 组合预测方法,可有效刻画塔河油田超深层缝洞型储层的强非均质特征,预测结果与实测数据吻合度高,可为同类碳酸盐岩储层横波速度预测提供高效可行的技术思路。
Abstract:ObjectiveShear wave velocity is a critical parameter that characterizes the physical and mechanical properties of subsurface media, and it plays an indispensable role in the exploration and development of oil and gas resources. In carbonate fracture-cavity reservoirs, complex lithologic assemblages and strong reservoir heterogeneity bring great challenges to shear wave velocity acquisition. Traditional rock physics models and empirical formulas are difficult to adapt to such complex geological conditions, resulting in low prediction accuracy and poor applicability.
MethodsTaking the ultra-deep fracture-cavity reservoirs in Tahe Oilfield as the research target, this study proposed a shear wave velocity prediction method using long short-term memory (LSTM) neural networks based on dimensionality reduction and reservoir classification. Firstly, the distorted logging curves were corrected by using valid undistorted logging data to guarantee the reliability of input datasets. Secondly, principal component analysis (PCA) was adopted to reduce the dimensionality of 11 logging parameters including acoustic slowness, density logging, and neutron logging, and five principal components were extracted to eliminate data redundancy. On the basis of imaging logging and electrical logging characteristics, support vector machine (SVM) was applied to divide reservoirs into six categories: Dissolved pores, fractures, intact bedrock, unfilled caves, sand-mud filled caves, and breccia-filled caves. Then, targeted LSTM deep learning models were established to realize classified shear wave velocity prediction for different reservoir types.
ResultsThe application results showed that the overall prediction accuracy of the proposed method reached 91%, representing a significant improvement over conventional empirical formulas and rock physics methods. Independent verification using blind wells further proved that the maximum correlation coefficient between predicted and measured shear wave velocity was up to 0.96. The predicted curves were highly consistent with measured data.
ConclusionThe proposed PCA-SVM-LSTM combined method can well describe the strong heterogeneity of ultra-deep fracture-cavity reservoirs in Tahe Oilfield, and the prediction results show good agreement with measured data. This method avoids the complicated rock physics modeling process and has the advantages of simple workflow and high computational efficiency. It provides an efficient and feasible technical reference for shear wave velocity prediction of similar carbonate fracture-cavity reservoirs.
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Key words:
- Tahe Oilfield /
- fracture-cavity reservoir /
- limestone cave /
- deep learning /
- shear wave prediction /
- LSTM
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表 1 PCA主成分贡献表
Table 1. Contribution rates of principal components from PCA
特征向量 LNRS LNRD GR AC DEN CNL SP CAL POR RC RM 特征值 方差贡献率/% 累计贡献率/% PCA1 −0.37 −0.36 0.35 0.35 −0.28 0.28 0.33 0.17 0.30 0.22 0.23 6.83 61.41 61.41 PCA2 0.19 0.22 −0.13 0.16 −0.39 0.17 −0.26 0.51 −0.20 −0.29 0.49 1.31 11.80 73.21 PCA3 −0.01 −0.02 0.10 −0.13 0.26 −0.29 −0.09 0.72 0.46 −0.08 −0.27 0.79 7.08 80.29 PCA4 −0.11 −0.13 0.13 0.14 −0.12 0.27 −0.06 −0.16 0.10 −0.80 −0.40 0.76 6.84 87.13 PCA5 −0.09 −0.11 0.20 0.09 −0.57 −0.67 −0.01 0.02 −0.31 0.02 −0.25 0.52 4.68 91.81 PCA6 0.04 0.07 −0.02 0.02 0.13 −0.48 0.40 −0.22 0.29 −0.41 0.53 0.36 3.23 95.04 PCA7 0.01 0.19 0.19 −0.25 0.20 0.13 0.63 0.31 −0.57 −0.15 −0.06 0.20 1.79 96.84 PCA8 −0.03 0.78 0.78 −0.23 0.21 −0.01 −0.43 −0.11 −0.12 −0.05 0.28 0.16 1.46 98.30 PCA9 0.17 0.10 0.10 −0.69 −0.52 0.17 0.17 −0.08 0.34 0.04 −0.04 0.14 1.25 99.55 PCA10 −0.51 −0.37 −0.37 −0.46 0 −0.05 −0.20 0.05 −0.13 −0.12 0.22 0.05 0.45 100.00 PCA11 0.72 0 0 0 0 0 0 0 0 0 0.04 0 0 100.00 注:RC. 深浅电阻率差;RM. 深浅电阻率比值 -
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