<p>The study presents simultaneous pre-stack seismic inversion and extended elastic impedance (EEI) analysis for the prediction of geomechanical parameters and in-situ stress fields in Asmari formation, Iran. Initially, simultaneous inversion (SI) was applied to pre-stack seismic data to derive elastic properties such as compressional wave velocity (Vp), shear wave velocity (Vs), and density (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">$\rho$</EquationSource> <EquationSource Format="MATHML"><math> <mi>ρ</mi> </math></EquationSource> </InlineEquation>). In the second stage, EEI inversion was conducted to determine the optimal chi angles (<InlineEquation ID="IEq2"> <EquationSource Format="TEX">$\chi$</EquationSource> <EquationSource Format="MATHML"><math> <mi>χ</mi> </math></EquationSource> </InlineEquation>) by the calculation of EEI spectra across various incident angles (<InlineEquation ID="IEq3"> <EquationSource Format="TEX">$\theta$</EquationSource> <EquationSource Format="MATHML"><math> <mi>θ</mi> </math></EquationSource> </InlineEquation>) to identify optimal <InlineEquation ID="IEq4"> <EquationSource Format="TEX">$\chi$</EquationSource> <EquationSource Format="MATHML"><math> <mi>χ</mi> </math></EquationSource> </InlineEquation> for maximum correlation with various parameters, including Vp, Vs, <InlineEquation ID="IEq5"> <EquationSource Format="TEX">$\rho$</EquationSource> <EquationSource Format="MATHML"><math> <mi>ρ</mi> </math></EquationSource> </InlineEquation>, Vp/Vs ratio, poisons ratio (<InlineEquation ID="IEq6"> <EquationSource Format="TEX">$\sigma$</EquationSource> <EquationSource Format="MATHML"><math> <mi>σ</mi> </math></EquationSource> </InlineEquation>), bulk modulus (K), young modulus (E), mu-rho (<InlineEquation ID="IEq7"> <EquationSource Format="TEX">$\mu \rho$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>μ</mi> <mi>ρ</mi> </mrow> </math></EquationSource> </InlineEquation>), lambda-rho (<InlineEquation ID="IEq8"> <EquationSource Format="TEX">$\lambda \rho$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>λ</mi> <mi>ρ</mi> </mrow> </math></EquationSource> </InlineEquation>), and brittleness (BRI). Then, the results of the SI were utilized within the framework of EEI to determine the distribution of geomechanical properties of Asmari formation at the selected optimal <InlineEquation ID="IEq9"> <EquationSource Format="TEX">$\chi$</EquationSource> <EquationSource Format="MATHML"><math> <mi>χ</mi> </math></EquationSource> </InlineEquation> angles. In the final stage, in-situ stresses and pore pressure were calculated. Through examining the correlation of different parameters with EEI data at various <InlineEquation ID="IEq10"> <EquationSource Format="TEX">$\chi$</EquationSource> <EquationSource Format="MATHML"><math> <mi>χ</mi> </math></EquationSource> </InlineEquation> angles, it was determined that the highest correlations for Vp, Vs, <InlineEquation ID="IEq11"> <EquationSource Format="TEX">$\rho$</EquationSource> <EquationSource Format="MATHML"><math> <mi>ρ</mi> </math></EquationSource> </InlineEquation>, Vp/Vs ratio, <InlineEquation ID="IEq12"> <EquationSource Format="TEX">$\lambda \rho$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>λ</mi> <mi>ρ</mi> </mrow> </math></EquationSource> </InlineEquation>, and <InlineEquation ID="IEq13"> <EquationSource Format="TEX">$\mu \rho$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>μ</mi> <mi>ρ</mi> </mrow> </math></EquationSource> </InlineEquation> are 0.99 (at <InlineEquation ID="IEq14"> <EquationSource Format="TEX">$\chi =0^\circ$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>χ</mi> <mo>=</mo> <msup> <mn>0</mn> <mo>∘</mo> </msup> </mrow> </math></EquationSource> </InlineEquation>), 0.99 (at <InlineEquation ID="IEq15"> <EquationSource Format="TEX">$\chi =-54^\circ$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>χ</mi> <mo>=</mo> <mo>-</mo> <msup> <mn>54</mn> <mo>∘</mo> </msup> </mrow> </math></EquationSource> </InlineEquation>), 0.98 (at <InlineEquation ID="IEq16"> <EquationSource Format="TEX">$\chi =-1^\circ$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>χ</mi> <mo>=</mo> <mo>-</mo> <msup> <mn>1</mn> <mo>∘</mo> </msup> </mrow> </math></EquationSource> </InlineEquation>), 0.99 (at <InlineEquation ID="IEq17"> <EquationSource Format="TEX">$\chi =36^\circ$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>χ</mi> <mo>=</mo> <msup> <mn>36</mn> <mo>∘</mo> </msup> </mrow> </math></EquationSource> </InlineEquation>), 0.98 (at <InlineEquation ID="IEq18"> <EquationSource Format="TEX">$\chi =17^\circ$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>χ</mi> <mo>=</mo> <msup> <mn>17</mn> <mo>∘</mo> </msup> </mrow> </math></EquationSource> </InlineEquation>), and 0.99 (at <InlineEquation ID="IEq19"> <EquationSource Format="TEX">$\chi =-45^\circ$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>χ</mi> <mo>=</mo> <mo>-</mo> <msup> <mn>45</mn> <mo>∘</mo> </msup> </mrow> </math></EquationSource> </InlineEquation>) respectively. The analysis revealed a comprehensive distribution of elastic and geomechanical parameters across the formation, indicating the presence of distinct carbonate and sandstone sections. Consequently, the results demonstrated significant reductions in <InlineEquation ID="IEq20"> <EquationSource Format="TEX">$\lambda \rho$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>λ</mi> <mi>ρ</mi> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq21"> <EquationSource Format="TEX">$\mu \rho$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>μ</mi> <mi>ρ</mi> </mrow> </math></EquationSource> </InlineEquation> attributes within the sandstone interval as compared to the carbonate interval. In contrast, <InlineEquation ID="IEq22"> <EquationSource Format="TEX">$\lambda \rho$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>λ</mi> <mi>ρ</mi> </mrow> </math></EquationSource> </InlineEquation> showed a more significant reduction due to its sensitivity to both reservoir fluid and lithology. In-situ stress calculations identified a predominance of reverse and strike-slip fault regimes, with no evidence of normal faulting. Thus, Asmari formation, especially the sandstone section, which has shale layers, is classified as an overpressure formation. Based on the study's findings, the EEI analysis is recommended as an effective approach for reservoir characterization and management. Therefore, application of this methodology in seismic exploration can bring about significant progress in the future.</p>

Geomechanical characterization of Asmari formation in the Dezful embayment via simultaneous inversion and extended elastic impedance techniques, SW Iran

期刊论文
发表日期：

2025年3月23日

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Ahsan Leisi,
Navid Shad Manaman

摘要

The study presents simultaneous pre-stack seismic inversion and extended elastic impedance (EEI) analysis for the prediction of geomechanical parameters and in-situ stress fields in Asmari formation, Iran. Initially, simultaneous inversion (SI) was applied to pre-stack seismic data to derive elastic properties such as compressional wave velocity (Vp), shear wave velocity (Vs), and density ( $\rho$ $ρ$ ). In the second stage, EEI inversion was conducted to determine the optimal chi angles ( $\chi$ $χ$ ) by the calculation of EEI spectra across various incident angles ( $\theta$ $θ$ ) to identify optimal $\chi$ $χ$ for maximum correlation with various parameters, including Vp, Vs, $\rho$ $ρ$ , Vp/Vs ratio, poisons ratio ( $\sigma$ $σ$ ), bulk modulus (K), young modulus (E), mu-rho ( $\mu \rho$ $μ ρ$ ), lambda-rho ( $\lambda \rho$ $λ ρ$ ), and brittleness (BRI). Then, the results of the SI were utilized within the framework of EEI to determine the distribution of geomechanical properties of Asmari formation at the selected optimal $\chi$ $χ$ angles. In the final stage, in-situ stresses and pore pressure were calculated. Through examining the correlation of different parameters with EEI data at various $\chi$ $χ$ angles, it was determined that the highest correlations for Vp, Vs, $\rho$ $ρ$ , Vp/Vs ratio, $\lambda \rho$ $λ ρ$ , and $\mu \rho$ $μ ρ$ are 0.99 (at $\chi =0^\circ$ $χ = 0^{\circ}$ ), 0.99 (at $\chi =-54^\circ$ $χ = - 54^{\circ}$ ), 0.98 (at $\chi =-1^\circ$ $χ = - 1^{\circ}$ ), 0.99 (at $\chi =36^\circ$ $χ = 36^{\circ}$ ), 0.98 (at $\chi =17^\circ$ $χ = 17^{\circ}$ ), and 0.99 (at $\chi =-45^\circ$ $χ = - 45^{\circ}$ ) respectively. The analysis revealed a comprehensive distribution of elastic and geomechanical parameters across the formation, indicating the presence of distinct carbonate and sandstone sections. Consequently, the results demonstrated significant reductions in $\lambda \rho$ $λ ρ$ and $\mu \rho$ $μ ρ$ attributes within the sandstone interval as compared to the carbonate interval. In contrast, $\lambda \rho$ $λ ρ$ showed a more significant reduction due to its sensitivity to both reservoir fluid and lithology. In-situ stress calculations identified a predominance of reverse and strike-slip fault regimes, with no evidence of normal faulting. Thus, Asmari formation, especially the sandstone section, which has shale layers, is classified as an overpressure formation. Based on the study's findings, the EEI analysis is recommended as an effective approach for reservoir characterization and management. Therefore, application of this methodology in seismic exploration can bring about significant progress in the future.