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Modified Bayesian iterative inversion method and its application to dolomite tight oil reservoirs prediction |
Qi-Qi MA, Zan-Dong SUN, Liu-Xin YANG |
College of Geophysics and Information Engineering,China University of Petroleum(Beijing),Beijing 102246,China |
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Abstract It is difficult to accurately predict the dolomite tight oil reservoir which has the characteristics of low porosity and low permeability by using the post-stack inversion,due to the small difference in acoustic impedance between the reservoir and its surrounding rock.Therefore,more abundant elastic information is needed.AVO inversion is an effective means to extract elastic information from pre-stack data.However,due to the noise and other factors,the pre-stack inversion equation has a strong ill-posed problem.Bayesian theory allows the construction of a regularization term by introducing a priori information about the model parameters,thereby effectively reducing the ill-posed problem of the inversion.Therefore,the modified Trivariate Cauchy constraint and the modified low-frequency constraint factor is introduced into the objective function,which can improve the ill-posed problem of the inversion,thus upgrading the accuracy of the inversion results.The iterative idea is used to address the non-linear nature of the proposed inverse operator.The P and S-wave velocity is updated in the iterations,which leads to more reliable results when applied to real data.Both the model data tests and the field data applications prove the validity and stability of the proposed method.Statistics show that,by using the proposed inversion method,the prediction accuracy rate of the reservoir thickness is as high as 89.5%.Therefore,this method has important reference significance for the exploration of similar siliceous reservoirs.
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Received: 27 September 2018
Published: 10 April 2019
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Comparison of Cauchy distribution constraint and modified Cauchy distribution constraint
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Comparison of inverted results of Rs in different iterations and theoretical data a—theory Rs;b—Rs obtained from the first iteration;c—the difference between the Rs obtained from the first iteration and the theoretical value;d—Rs obtained from the second iteration;e—the difference between the Rs obtained from the second iteration and the theoretical value;f—Rs obtained from the third iteration;g—the difference between the Rs obtained from the second iteration and the theoretical value
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Synthetic gathers a—Noise-free;b—S/N=2
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Comparison of inversion results with real logging data a—inverted P-impedance results (noise free);b—inverted S-impedance results (noise free);c—inverted density results;d—inverted P-impedance results (S/N=2);e—inverted S-impedance results (S/N=2);f—inverted density results (S/N=2)
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| 方法 | 纵波阻抗相关系数 | 横波阻抗相关系数 | 密度相关系数 | 无噪声 | 新方法 | 0.9993 | 0.9987 | 0.9937 | | 常规方法 | 0.9988 | 0.9970 | 0.9851 | 有噪声 | 新方法 | 0.9903 | 0.9742 | 0.8684 | | 常规方法 | 0.9766 | 0.9433 | 0.7873 |
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Comparison of the correlation coefficients of inversion results
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Cross-plot of P-impedance versus S-impedance of dolomite tight oil reservoirs
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Comparison of inverted results of target layer a—inverted Ip by conventional method;b—inverted Is by conventional method;c—inverted Ip by new method;d—inverted Is by new method
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Comparison of inverted results of pseudo and well-logging data a—P-impedance;b—S-impedance
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Flow chart of reservoir thickness prediction
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The prediction thickness of high-quality reservoirs of target layer
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井名 | 实际厚度/m | 预测厚度/m | 吻合率/% | 井名 | 实际厚度/m | 预测厚度/m | 吻合率/% | Well 1 | 59.56 | 50 | 84 | Well 9 | 87 | 92 | 94 | Well 2 | 9.79 | 11 | 88 | Well 10 | 53.54 | 54 | 99 | Well 3 | 72.5 | 71 | 98 | Well 11 | 42.56 | 36 | 85 | Well 4 | 47.3 | 48.5 | 95 | Well 12 | 92.5 | 79.19 | 86 | Well 5 | 62.87 | 54 | 86 | Well 15 | 71.31 | 57 | 80 | Well 6 | 49 | 49.8 | 98 | Well 16 | 24.97 | 27 | 92 | Well 7 | 65.1 | 80.9 | 76 | Well 18 | 55.5 | 57.2 | 97 | Well 8 | 54.02 | 51.05 | 95 | Well 22 | 80 | 94 | 83 | | 总吻合率/% | | | | 89.75 | | |
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Statistics of actual dolomite thickness and predicted thickness in the study area
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