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| A method for predicting the brittleness and fracture parameters of shale gas reservoirs based on prestack direct inversion |
| SHI Xue-Wen1,2, WANG Chang1,2, ZHANG Dong-Jun1,2, FENG Yan-Wen1,2 |
1. Shale Gas Research Institute, Southwest Oil & Gasfield Company,PetroChina, Chengdu 610051, China
2. Sichuan Key Laboratory of Shale Gas Evaluation and Exploitation, Chengdu 610051, China |
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Abstract The conventional inversion of anisotropic media is often constrained by assumptions of narrow-angle incidence and weak changes in stratigraphic properties.Moreover,the prediction of rock elastic parameters typically involves linear inversion and indirect fitting,leading to less accurate and reliable inversion results of petrophysical parameters for anisotropic formations.Hence,this study derived the petrophysical models of Young's modulus,Poisson's ratio,and fracture parameters for vertical transverse isotropy(VTI) media.Based on the precise VTI reflection coefficient equation,this study proposed a Bayesian anisotropic nonlinear direct inversion method,constrained by the L1 norm,to predict the brittleness and fracture parameters of shale gas reservoirs through direct inversion.The proposed method yielded satisfactory application results in a study area of shale gas in Southwest China,offering a novel technique for characterizing shale gas reservoirs.
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Received: 22 January 2025
Published: 07 August 2025
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| E/GPa | σ | Vp/
(m·s-1) | Vs/
(m·s-1) | ρ/
(kg·m-3) | δN | δT | | 上层页岩 | 21.28 | 0.272 | 3268 | 1829 | 2500 | 0.248 | 0.090 | | 下层页岩 | 33.27 | 0.160 | 3678 | 2339 | 2620 | 0.056 | 0.024 |
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The double-layer model 1 of gas-bearing shales
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| E/GPa | σ | Vp/
(m·s-1) | Vs/
(m·s-1) | ρ/
(kg·m-3) | δN | δT | | 上层页岩 | 17.47 | 0.256 | 2960 | 1695 | 2420 | 0.181 | 0.068 | | 下层页岩 | 9.57 | 0.324 | 2430 | 1240 | 2350 | 0.104 | 0.032 |
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The double-layer model 2 of gas-bearing shales
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The accuracy analysis result of reflection coefficient equations based on double-layer gas-bearing shales model 1
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The accuracy analysis result of reflection coefficient equations based on double-layer gas-bearing shales model 2
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| 流程 | 描述 | | 步骤1 | 初始化算法,设置马尔可夫链的数量及每条马尔可夫链的最大循环数 | | 步骤2 | 选择初始模型作为首次迭代的模型,并以此作为每条马尔可夫链的初始状态 | | 步骤3 | 在每条马尔可夫链中,由特定均值和方差的建议分布生成一个新的候选模型 | | 步骤4 | 根据所建立的后验概率目标函数,计算新的候选模型的接受概率 | | 步骤5 | 以一定概率接受新的候选模型 | | 步骤6 | 返回固定状态下的值作为单个马尔可夫链预测的结果,并以此计算每条马尔科夫链的候选模型及接受情况 | | 步骤7 | 取多此循环后稳定的多条马尔科夫链的平均值作为最终的反演结果 |
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Solution flow of McMC algorithm nonlinear optimization
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The rock physical models to be inverted
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Forward synthetic seismogram
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The inversion results at the synthesized seismogram of noise free
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The inversion results at the synthesized seismogram with signal to noise ratio(SNR) equals 10
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The absolute values of the error between the inversion results and the real models
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The actual pre-stack cross seismic data profiles
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The nonlinear inversion results(left) and indirect fitting results from conventional linear inversion(right) elastic parameters of actual pre-stack seismic profiles
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Interlayer slices of nonlinear actual pre-stack seismic inversion results of brittleness and fractural parameters
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