Working as a lecturer in Geophysics at Institute of Geology, University of the Punjab, Lahore, Pakistan. Currently doing my research in the field of rock physics and reservoir geophysics. Address: Lahore, Punjab, Pakistan
SUMMARY Seismic inversion of amplitude versus offset (AVO) data in viscoelastic media can potenti... more SUMMARY Seismic inversion of amplitude versus offset (AVO) data in viscoelastic media can potentially provide high-resolution subsurface models of seismic velocities and attenuation from offset/angle seismic gathers. P- and S-wave quality factors (Q), whose inverse represent a measure of attenuation, depend on reservoir rock and pore fluid properties, in particular, saturation, permeability, porosity, fluid viscosity and lithology; however, these quality factors are rarely taken into account in seismic AVO inversion. For this reason, in this work, we aim to integrate quality factors derived from physically based models in AVO inversion by proposing a gradient descent optimization-based inversion technique to predict the unknown model properties (P- and S-wave velocities, the related quality factors and density). The proposed inversion minimizes the non-linear least-squares misfit with the observed data. The optimal solution is iteratively obtained by optimizing the data misfit using...
Summary Lithology and pore fluids prediction are two prime goals in the seismic characterization ... more Summary Lithology and pore fluids prediction are two prime goals in the seismic characterization of reservoir rock. Extended elastic impedance (EEI) is one of the more promising attribute used to differentiate the reservoir fluids. However, the results of EEI are more depend on the chi-angles that can be computed by computing the maximum correlation coefficients EEI with other elastic properties. In the present study we defined another way to compute the chi-angles and it given very similar results to that of maximum correlation coefficients. We have also defined the chi-angles for various elastic and petrophysical properties to extract the information about reservoir fluids and lithologies.
ABSTRACT Punjab Platform is one of the least explored areas in Pakistan. The reasons are: lack of... more ABSTRACT Punjab Platform is one of the least explored areas in Pakistan. The reasons are: lack of favorable mature source rock in the area, shortening of structural traps, and its distance from collision zone. The rocks in Punjab Platform represent the diverse system of clastics to carbonates with several sea-level fluctuations within the basin. These sea level variations represent prograding clinoforms, truncation with tertiary unconformity and pinch out in Goru Formation. The petrophysical analysis of different wells in Punjab platform shows that it was first transgressive cycle and then regressive cycle. Seismic data acquired in different areas of Punjab Platform indicate the possibility of stratigraphic traps in the sedimentary package from Jurassic to Eocene especially in the Cretaceous sandstone units. Such traps if found in Punjab Platform offer preferred location for exploratory drilling. The presence of sand dunes weaker the resolution of seismic data and makes it difficult for stratigraphic interpretation. However, numerous gas discoveries have been made in Lumshiwal Formation of Cretaceous and Samanasuk Formation of Jurassic, demonstrating to an extent, optimistic hydrocarbon prospect in the area. After the interpretation of seismic sequence stratigraphic and the analysis of seismic attributes, a framework of complete petroleum system in Goru Formation is developed, which shows that shale in lower Goru acting as a source rock and sand beds in lower part of Goru consider being a reservoir rock. Past exploration has been mainly focused on drilling structural traps, whereas we emphasize stratigraphic traps especially those modified by erosion during unconformities should be preferred exploration objectives. Probable structural faults and progrades at Cretaceous level which are showing truncation at Tertiary Unconformity were identified on several lines that have been marked on the stack sections.
The present study demonstrates the application of seismic petrophysics and amplitude versus angle... more The present study demonstrates the application of seismic petrophysics and amplitude versus angle (AVA) forward modeling to identify the reservoir fluids, discriminate their saturation levels and natural gas composition. Two case studies of the Lumshiwal Formation (mainly sandstone) of the Lower Cretaceous age have been studied from the Kohat Sub-basin and the Middle Indus Basin of Pakistan. The conventional angle-dependent reflection amplitudes such as P converted P (RPP) and S (RPS), S converted S (RSS) and P (RSP) and newly developed AVA attributes (ΔRPP, ΔRPS, ΔRSS, and ΔRSP) are analyzed at different gas saturation levels in the reservoir rock. These attributes are generated by taking the differences between the water wet reflection coefficient and the reflection coefficient at unknown gas saturation. Intercept (A) and gradient (B) attributes are also computed and cross-plotted at different gas compositions and gas/water scenarios to define the AVO class of reservoir sands. The numerical simulation reveals that ΔRPP, ΔRPS, ΔRSS, and ΔRSP are good indicators and able to distinguish low and high gas saturation with a high level of confidence as compared to conventional reflection amplitudes such as P-P, P-S, S-S and S-P. In A-B cross-plots, the gas lines move towards the fluid (wet) lines as the proportion of heavier gases increase in the Lumshiwal Sands. Because of the upper contacts with different sedimentary rocks (Shale/Limestone) in both wells, the same reservoir sand exhibits different response similar to AVO classes like the class I and class IV. This study will help to analyze gas sands by using amplitude-based attributes as direct gas indicators in further gas drilling wells in clastic successions.
Lower Goru sand intervals of the Cretaceous age in Kadanwari field of the middle Indus Basin, Pak... more Lower Goru sand intervals of the Cretaceous age in Kadanwari field of the middle Indus Basin, Pakistan, are interpreted as reservoir intervals. Based on seismic interpretation and geology, several wells were drilled in these sands. However, most of the wells drilled were dry and declared abundant because highly saturated brine was encountered with minute amount of hydrocarbon gas. The main reason for drilling dry wells was limitation of seismic reflection data to differentiate seismic response of hydrocarbon-saturated reservoir interval from non-hydrocarbon-saturated interval. Amplitude versus offset (AVO) analysis is widely used to differentiate hydrocarbon intervals from background lithology. In this work, AVO-derived attributes are used for fluid discrimination in the sand intervals. Amplitude differences are associated with density and compressibility of fluid under in situ temperature and pressure conditions of the reservoir interval. The results reveal that seismic amplitude anomalies associated with AVO analysis can differentiate hydrocarbon fluids from non-hydrocarbon fluids and thus can optimize the exploration of gas. The gas sand anomaly in the study area is of weak impedance as compared to brine sand. The intercept and fluid factor are very promising attribute pairs to discriminate gas sands from background sands. The results may be helpful to discriminate low gas saturation or fizz water from high gas saturation.
From the last few decades, the amplitude versus offset (AVO) analysis tools are widely used by ex... more From the last few decades, the amplitude versus offset (AVO) analysis tools are widely used by exploration, development and production teams to differentiate the reservoir fluids, their saturation and the lithologies in clastic depositional sFrom the last few decades, the amplitude versus offset (AVO) analysis tools are widely used by exploration, development and production teams to differentiate the reservoir fluids, their saturation and the lithologies in clastic depositional settings. Conventional AVO analysis involves the computation of intercept (I) and gradient (G) from amplitudes of reflected P-waves as function of incident angle or from the seismic parameters at reservoir interface. Various AVO attributes such as intercept, gradient, Poisson reflectivity (PR), fluid factor (ΔF), P and S wave normal incident reflection coefficients (RP and RS) and their difference are applied in the known gas field, Kadanwari, Lower Indus Basin of Pakistan. Our analysis reveals that the gas s...
The world focus is turned to exploitation of the unconventional resources such as sahle gas to fu... more The world focus is turned to exploitation of the unconventional resources such as sahle gas to full fill the energy needs. However, geophysical characterization of the organic rich shales are still challenging because the elastic, seismic and petrophysical properties of these rocks vary strongly with change in total organic carbon (TOC), thermal maturity and mineralogy. The Sembar Formation of Lower Cretaceous, widely distributed in southern and central Indus basin of Pakistan, has large potential of shale gas plays. An improved rock physics model is opted to incorporate TOC effects, in addition to other rock physics parameters such as porosity, fluid saturation, mineralogy, formation temperature and pressure to understand the thermal maturity and organic contents on seismic and rock physics properties of shale gas plays. The rock physics parameters are extracted by using wireline log data. The results reveal the seismic response and rock physics properties of shale gas strongly aff...
Naturally occurring gas hydrates composed of methane, propane or ethane molecules and water molec... more Naturally occurring gas hydrates composed of methane, propane or ethane molecules and water molecule are potential future energy source. A large amount of methane gas hydrate is present in the world sedimentary basins. A significant amount of gas hydrates is interpreted through seismic reflection data to be present in the sediments of the convergent continental margin of Pakistan. However, the seismic character of these hydrates bearing sediments was not well understood. Rock physics modeling is adopted to define seismic behavior of these sediments. The rock physics model based on the effective medium theory was found to be good one for seismic characterization of the hydrate-bearing sediments. Amplitude versus offset (AVO) attributes of bottom simulating reflector (BSR) is coupled with rock physics models to characterize the seismic properties of gas hydrate bearing sediments. Based on this coupling the saturation of gas hydrates and free gas preset beneath BSR of the continental m...
Partially saturated reservoirs are one of the major sources of seismic wave attenuation, modulus ... more Partially saturated reservoirs are one of the major sources of seismic wave attenuation, modulus defect and velocity dispersion in real seismic data. The main attenuation and dispersion phenomenon is wave induced fluid flow due to the heterogeneity in pore fluids or porous rock. The identification of pore fluid type, saturation and distribution pattern within the pore space is of great significance as several seismic and petrophysical properties of porous rocks are largely affected by fluid type, saturation and fluid distribution pattern. Based on Gassmann-Wood and Gassmann- Hill rock physics models modulus defect, velocity dispersion and attenuation in Jurassic siliclastic partially-saturated rocks are studied. For this purpose two saturation patterns - uniform and patchy - are considered within the pore spaces in two frequency regimes i.e., lower frequency and higher frequency. The results reveal that at low enough frequency where saturation of liquid and gas is uniform, the seismic velocity and bulk modulus are lower than at higher frequency where saturation of fluid mixture is in the form of patches. The velocity dispersion and attenuation is also modeled at different levels of gas saturation. It is found that the maximum attenuation and velocity dispersion is at low gas saturation. Therefore, the dispersion and attenuation can provide a potential way to predict gas saturation and can be used as a property to differentiate low from high gas saturation.
Seismic inversion of amplitude versus offset (AVO) data in viscoelastic media can potentially pro... more Seismic inversion of amplitude versus offset (AVO) data in viscoelastic media can potentially provide high-resolution subsurface models of seismic velocities and attenuation from offset/angle seismic gathers. P-and S-wave quality factors (Q), whose inverse represent a measure of attenuation, depend on reservoir rock and pore fluid properties, in particular, saturation, permeability, porosity, fluid viscosity and lithology; however, these quality factors are rarely taken into account in seismic AVO inversion. For this reason, in this work, we aim to integrate quality factors derived from physically based models in AVO inversion by proposing a gradient descent optimization-based inversion technique to predict the unknown model properties (P-and S-wave velocities, the related quality factors and density). The proposed inversion minimizes the non-linear least-squares misfit with the observed data. The optimal solution is iteratively obtained by optimizing the data misfit using a second-order limited-memory quasi-Newton technique. The forward model is performed in the frequency-frequency-angle domain based on a convolution of broad-band signals and a linearized viscoelastic frequencydependent AVO (FAVO) equation. The optimization includes the adjoint-state-based gradients with the Lagrangian formulation to improve the efficiency of the non-linear seismic FAVO inversion process. The inversion is tested on synthetic seismic data, in 1-D and 2-D, with and without noise. The sensitivity for seismic quality factors is evaluated using various rock physics models for seismic attenuation and quality factors. The results demonstrate that the proposed inversion method reliably retrieves the unknown elastic and an-elastic properties with good convergence and accuracy. The stability of the inverse solution especially seismic quality factors estimation relies on the noise level of the seismic data. We further investigate the uncertainty of the solution as a function of the variability of the initial models.
Pre-stack AVO inversion of seismic data is a modeling tool for estimating subsurface elastic prop... more Pre-stack AVO inversion of seismic data is a modeling tool for estimating subsurface elastic properties. Our focus is on the model-based inversion method where then unknown variables are estimated by minimizing the misfit to the observed data. Standard approaches for non-linear AVO inversion are based on the gradient descent optimization algorithms that require the calculation of the gradient equations of the objective function. To improve the accuracy and efficiency of these methods, we developed a technique that uses an implementation of the adjoint-state-based gradient computation. The inversion algorithm relies on three basic modeling components consisting of a convolution-based forward model using a linearized approximation of the Zoeppritz equation, the definition of the objective function, and the adjoint-computed gradient. To achieve an accurate solution, we choose a second-order optimization algorithm known as the Limited memory-BFGS (L-BFGS) that implicitly approximates the inverse Hessian matrix. This approach is more efficient than traditional optimization methods. The main novelty of the proposed approach is the derivation of the adjoint-state equations for the gradient of the objective function. The application of the proposed method is demonstrated using 1D and 2D synthetic datasets based on data from the Edvard Grieg oil field. The seismic data for these applications is generated by using both convolutional modeling and finite difference methods. The results of the proposed method are accurate and the computational approach is efficient. The results show that the algorithm reliably retrieves the elastic variables, P-and S-wave velocities and density for both convolutional and finite difference models.
SUMMARY Seismic inversion of amplitude versus offset (AVO) data in viscoelastic media can potenti... more SUMMARY Seismic inversion of amplitude versus offset (AVO) data in viscoelastic media can potentially provide high-resolution subsurface models of seismic velocities and attenuation from offset/angle seismic gathers. P- and S-wave quality factors (Q), whose inverse represent a measure of attenuation, depend on reservoir rock and pore fluid properties, in particular, saturation, permeability, porosity, fluid viscosity and lithology; however, these quality factors are rarely taken into account in seismic AVO inversion. For this reason, in this work, we aim to integrate quality factors derived from physically based models in AVO inversion by proposing a gradient descent optimization-based inversion technique to predict the unknown model properties (P- and S-wave velocities, the related quality factors and density). The proposed inversion minimizes the non-linear least-squares misfit with the observed data. The optimal solution is iteratively obtained by optimizing the data misfit using...
Summary Lithology and pore fluids prediction are two prime goals in the seismic characterization ... more Summary Lithology and pore fluids prediction are two prime goals in the seismic characterization of reservoir rock. Extended elastic impedance (EEI) is one of the more promising attribute used to differentiate the reservoir fluids. However, the results of EEI are more depend on the chi-angles that can be computed by computing the maximum correlation coefficients EEI with other elastic properties. In the present study we defined another way to compute the chi-angles and it given very similar results to that of maximum correlation coefficients. We have also defined the chi-angles for various elastic and petrophysical properties to extract the information about reservoir fluids and lithologies.
ABSTRACT Punjab Platform is one of the least explored areas in Pakistan. The reasons are: lack of... more ABSTRACT Punjab Platform is one of the least explored areas in Pakistan. The reasons are: lack of favorable mature source rock in the area, shortening of structural traps, and its distance from collision zone. The rocks in Punjab Platform represent the diverse system of clastics to carbonates with several sea-level fluctuations within the basin. These sea level variations represent prograding clinoforms, truncation with tertiary unconformity and pinch out in Goru Formation. The petrophysical analysis of different wells in Punjab platform shows that it was first transgressive cycle and then regressive cycle. Seismic data acquired in different areas of Punjab Platform indicate the possibility of stratigraphic traps in the sedimentary package from Jurassic to Eocene especially in the Cretaceous sandstone units. Such traps if found in Punjab Platform offer preferred location for exploratory drilling. The presence of sand dunes weaker the resolution of seismic data and makes it difficult for stratigraphic interpretation. However, numerous gas discoveries have been made in Lumshiwal Formation of Cretaceous and Samanasuk Formation of Jurassic, demonstrating to an extent, optimistic hydrocarbon prospect in the area. After the interpretation of seismic sequence stratigraphic and the analysis of seismic attributes, a framework of complete petroleum system in Goru Formation is developed, which shows that shale in lower Goru acting as a source rock and sand beds in lower part of Goru consider being a reservoir rock. Past exploration has been mainly focused on drilling structural traps, whereas we emphasize stratigraphic traps especially those modified by erosion during unconformities should be preferred exploration objectives. Probable structural faults and progrades at Cretaceous level which are showing truncation at Tertiary Unconformity were identified on several lines that have been marked on the stack sections.
The present study demonstrates the application of seismic petrophysics and amplitude versus angle... more The present study demonstrates the application of seismic petrophysics and amplitude versus angle (AVA) forward modeling to identify the reservoir fluids, discriminate their saturation levels and natural gas composition. Two case studies of the Lumshiwal Formation (mainly sandstone) of the Lower Cretaceous age have been studied from the Kohat Sub-basin and the Middle Indus Basin of Pakistan. The conventional angle-dependent reflection amplitudes such as P converted P (RPP) and S (RPS), S converted S (RSS) and P (RSP) and newly developed AVA attributes (ΔRPP, ΔRPS, ΔRSS, and ΔRSP) are analyzed at different gas saturation levels in the reservoir rock. These attributes are generated by taking the differences between the water wet reflection coefficient and the reflection coefficient at unknown gas saturation. Intercept (A) and gradient (B) attributes are also computed and cross-plotted at different gas compositions and gas/water scenarios to define the AVO class of reservoir sands. The numerical simulation reveals that ΔRPP, ΔRPS, ΔRSS, and ΔRSP are good indicators and able to distinguish low and high gas saturation with a high level of confidence as compared to conventional reflection amplitudes such as P-P, P-S, S-S and S-P. In A-B cross-plots, the gas lines move towards the fluid (wet) lines as the proportion of heavier gases increase in the Lumshiwal Sands. Because of the upper contacts with different sedimentary rocks (Shale/Limestone) in both wells, the same reservoir sand exhibits different response similar to AVO classes like the class I and class IV. This study will help to analyze gas sands by using amplitude-based attributes as direct gas indicators in further gas drilling wells in clastic successions.
Lower Goru sand intervals of the Cretaceous age in Kadanwari field of the middle Indus Basin, Pak... more Lower Goru sand intervals of the Cretaceous age in Kadanwari field of the middle Indus Basin, Pakistan, are interpreted as reservoir intervals. Based on seismic interpretation and geology, several wells were drilled in these sands. However, most of the wells drilled were dry and declared abundant because highly saturated brine was encountered with minute amount of hydrocarbon gas. The main reason for drilling dry wells was limitation of seismic reflection data to differentiate seismic response of hydrocarbon-saturated reservoir interval from non-hydrocarbon-saturated interval. Amplitude versus offset (AVO) analysis is widely used to differentiate hydrocarbon intervals from background lithology. In this work, AVO-derived attributes are used for fluid discrimination in the sand intervals. Amplitude differences are associated with density and compressibility of fluid under in situ temperature and pressure conditions of the reservoir interval. The results reveal that seismic amplitude anomalies associated with AVO analysis can differentiate hydrocarbon fluids from non-hydrocarbon fluids and thus can optimize the exploration of gas. The gas sand anomaly in the study area is of weak impedance as compared to brine sand. The intercept and fluid factor are very promising attribute pairs to discriminate gas sands from background sands. The results may be helpful to discriminate low gas saturation or fizz water from high gas saturation.
From the last few decades, the amplitude versus offset (AVO) analysis tools are widely used by ex... more From the last few decades, the amplitude versus offset (AVO) analysis tools are widely used by exploration, development and production teams to differentiate the reservoir fluids, their saturation and the lithologies in clastic depositional sFrom the last few decades, the amplitude versus offset (AVO) analysis tools are widely used by exploration, development and production teams to differentiate the reservoir fluids, their saturation and the lithologies in clastic depositional settings. Conventional AVO analysis involves the computation of intercept (I) and gradient (G) from amplitudes of reflected P-waves as function of incident angle or from the seismic parameters at reservoir interface. Various AVO attributes such as intercept, gradient, Poisson reflectivity (PR), fluid factor (ΔF), P and S wave normal incident reflection coefficients (RP and RS) and their difference are applied in the known gas field, Kadanwari, Lower Indus Basin of Pakistan. Our analysis reveals that the gas s...
The world focus is turned to exploitation of the unconventional resources such as sahle gas to fu... more The world focus is turned to exploitation of the unconventional resources such as sahle gas to full fill the energy needs. However, geophysical characterization of the organic rich shales are still challenging because the elastic, seismic and petrophysical properties of these rocks vary strongly with change in total organic carbon (TOC), thermal maturity and mineralogy. The Sembar Formation of Lower Cretaceous, widely distributed in southern and central Indus basin of Pakistan, has large potential of shale gas plays. An improved rock physics model is opted to incorporate TOC effects, in addition to other rock physics parameters such as porosity, fluid saturation, mineralogy, formation temperature and pressure to understand the thermal maturity and organic contents on seismic and rock physics properties of shale gas plays. The rock physics parameters are extracted by using wireline log data. The results reveal the seismic response and rock physics properties of shale gas strongly aff...
Naturally occurring gas hydrates composed of methane, propane or ethane molecules and water molec... more Naturally occurring gas hydrates composed of methane, propane or ethane molecules and water molecule are potential future energy source. A large amount of methane gas hydrate is present in the world sedimentary basins. A significant amount of gas hydrates is interpreted through seismic reflection data to be present in the sediments of the convergent continental margin of Pakistan. However, the seismic character of these hydrates bearing sediments was not well understood. Rock physics modeling is adopted to define seismic behavior of these sediments. The rock physics model based on the effective medium theory was found to be good one for seismic characterization of the hydrate-bearing sediments. Amplitude versus offset (AVO) attributes of bottom simulating reflector (BSR) is coupled with rock physics models to characterize the seismic properties of gas hydrate bearing sediments. Based on this coupling the saturation of gas hydrates and free gas preset beneath BSR of the continental m...
Partially saturated reservoirs are one of the major sources of seismic wave attenuation, modulus ... more Partially saturated reservoirs are one of the major sources of seismic wave attenuation, modulus defect and velocity dispersion in real seismic data. The main attenuation and dispersion phenomenon is wave induced fluid flow due to the heterogeneity in pore fluids or porous rock. The identification of pore fluid type, saturation and distribution pattern within the pore space is of great significance as several seismic and petrophysical properties of porous rocks are largely affected by fluid type, saturation and fluid distribution pattern. Based on Gassmann-Wood and Gassmann- Hill rock physics models modulus defect, velocity dispersion and attenuation in Jurassic siliclastic partially-saturated rocks are studied. For this purpose two saturation patterns - uniform and patchy - are considered within the pore spaces in two frequency regimes i.e., lower frequency and higher frequency. The results reveal that at low enough frequency where saturation of liquid and gas is uniform, the seismic velocity and bulk modulus are lower than at higher frequency where saturation of fluid mixture is in the form of patches. The velocity dispersion and attenuation is also modeled at different levels of gas saturation. It is found that the maximum attenuation and velocity dispersion is at low gas saturation. Therefore, the dispersion and attenuation can provide a potential way to predict gas saturation and can be used as a property to differentiate low from high gas saturation.
Seismic inversion of amplitude versus offset (AVO) data in viscoelastic media can potentially pro... more Seismic inversion of amplitude versus offset (AVO) data in viscoelastic media can potentially provide high-resolution subsurface models of seismic velocities and attenuation from offset/angle seismic gathers. P-and S-wave quality factors (Q), whose inverse represent a measure of attenuation, depend on reservoir rock and pore fluid properties, in particular, saturation, permeability, porosity, fluid viscosity and lithology; however, these quality factors are rarely taken into account in seismic AVO inversion. For this reason, in this work, we aim to integrate quality factors derived from physically based models in AVO inversion by proposing a gradient descent optimization-based inversion technique to predict the unknown model properties (P-and S-wave velocities, the related quality factors and density). The proposed inversion minimizes the non-linear least-squares misfit with the observed data. The optimal solution is iteratively obtained by optimizing the data misfit using a second-order limited-memory quasi-Newton technique. The forward model is performed in the frequency-frequency-angle domain based on a convolution of broad-band signals and a linearized viscoelastic frequencydependent AVO (FAVO) equation. The optimization includes the adjoint-state-based gradients with the Lagrangian formulation to improve the efficiency of the non-linear seismic FAVO inversion process. The inversion is tested on synthetic seismic data, in 1-D and 2-D, with and without noise. The sensitivity for seismic quality factors is evaluated using various rock physics models for seismic attenuation and quality factors. The results demonstrate that the proposed inversion method reliably retrieves the unknown elastic and an-elastic properties with good convergence and accuracy. The stability of the inverse solution especially seismic quality factors estimation relies on the noise level of the seismic data. We further investigate the uncertainty of the solution as a function of the variability of the initial models.
Pre-stack AVO inversion of seismic data is a modeling tool for estimating subsurface elastic prop... more Pre-stack AVO inversion of seismic data is a modeling tool for estimating subsurface elastic properties. Our focus is on the model-based inversion method where then unknown variables are estimated by minimizing the misfit to the observed data. Standard approaches for non-linear AVO inversion are based on the gradient descent optimization algorithms that require the calculation of the gradient equations of the objective function. To improve the accuracy and efficiency of these methods, we developed a technique that uses an implementation of the adjoint-state-based gradient computation. The inversion algorithm relies on three basic modeling components consisting of a convolution-based forward model using a linearized approximation of the Zoeppritz equation, the definition of the objective function, and the adjoint-computed gradient. To achieve an accurate solution, we choose a second-order optimization algorithm known as the Limited memory-BFGS (L-BFGS) that implicitly approximates the inverse Hessian matrix. This approach is more efficient than traditional optimization methods. The main novelty of the proposed approach is the derivation of the adjoint-state equations for the gradient of the objective function. The application of the proposed method is demonstrated using 1D and 2D synthetic datasets based on data from the Edvard Grieg oil field. The seismic data for these applications is generated by using both convolutional modeling and finite difference methods. The results of the proposed method are accurate and the computational approach is efficient. The results show that the algorithm reliably retrieves the elastic variables, P-and S-wave velocities and density for both convolutional and finite difference models.
8th Saint Petersburg International Conference & Exhibition , 2018
Lithology and pore fluids prediction are two prime goals in the seismic characterization of reser... more Lithology and pore fluids prediction are two prime goals in the seismic characterization of reservoir rock. Extended elastic impedance (EEI) is one of the more promising attribute used to differentiate the reservoir fluids. However, the results of EEI are more depend on the chi-angles that can be computed by computing the maximum correlation coefficients EEI with other elastic properties. In the present study we defined another way to compute the chi-angles and it given very similar results to that of maximum correlation coefficients. We have also defined the chi-angles for various elastic and petrophysical properties to extract the information about reservoir fluids and lithologies.
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