Elastic Impedance and AVA Inversion Quiz

Seismic amplitudes = Widely used for qualitative interpretation to detect hydrocarbon anomalies Reflection coefficient = Proportional to the amplitude of seismic reflection at normal incidence Reservoir properties = Information contained in amplitudes could be correlated with lithology changes, porosity changes, and type of fluid in the subsurface reservoir Seismic inversion = Process used to quantitatively describe reservoir properties

Exploring amplitudes for reservoir properties = Using amplitudes to quantitatively describe reservoir properties Defining the inverse problem = Establishing the problem for seismic reservoir characterization Reviewing seismic inversion approaches = Discussing different methods and processes of inversion Role of seismic inversion in exploration & production = Understanding the significance of seismic inversion in oil and gas operations

Amplitude of seismic reflection is proportional to reflection coefficient at normal incidence = Reflection Coefficient Amplitudes correlated with lithology changes, porosity changes, and fluid type in reservoirs = Reservoir properties Qualitative interpretation for detecting hydrocarbon anomalies = Seismic amplitudes Quantitatively describing reservoir properties using seismic data = Seismic inversion

<p>Tuning effect = Interference in seismic reflections due to layer thickness Duality between layer thickness and properties = Difficulty in distinguishing between changes in layer thickness and properties based on seismic data alone Amplitudes as interface property = Dependency on impedance contrast between two layers Geostatistical methods = Using secondary data to guide porosity estimation</p> Signup and view all the answers

<p>Correlation between parameters = Indication of relationship strength, not dependence Collocated Cokriging = Using secondary data like Seismic Amplitudes for porosity estimation Soft-impedance reservoir = Increase in porosity leading to higher reflection amplitude due to impedance contrast Reflection coefficients by Zoeppritz equations = Dependence on impedance difference for normal-incident P-wave</p> Signup and view all the answers

<p>Quantitative interpretation = Correlating seismic attributes with reservoir properties using geostatistical methods Forward modeling = Controlling the choice of sensible attributes for correlation Seismic Amplitudes as secondary data = Used to guide porosity estimation away from wells Amplitude changes due to rock properties = Challenging for qualitative interpretation</p> Signup and view all the answers

<p>Misinterpretation due to tuning effect = Difficulty in distinguishing closely spaced reflectors and subsurface properties Challenges in uniquely determining subsurface properties = Influence of layer thickness and properties on seismic response Minimizing interface effects on amplitudes = Transforming seismic data into layer properties like acoustic impedance Need for additional constraints in interpretation = Resolving ambiguities between layer thickness and properties</p> Signup and view all the answers

<p>Wavelet estimation = Key to a successful inversion Low Frequency Model = Based on well logs and structural framework Quality Control = Important at all stages of the process Objective Function = Used to minimize in modern algorithms</p> Signup and view all the answers

<p>Seismic Inversion = Finding simple solution consistent with seismic and well data Acoustic Inversion = Obtaining acoustic impedance from full stack data Objective Function = Function used for minimization in algorithms Wavelet Estimation = Key process done at the well location</p> Signup and view all the answers

<p>Seismic data (post-stack data or pre-stack gathers and migration velocities) = Input data for inversion workflow Well information (sonic and density logs and VSP data) = Used for well to seismic tie and wavelet estimation Structural interpretation (horizons and faults) = Incorporated in creating the Low Frequency Model Wavelets = Input for the inversion to find reflectivity away from wells</p> Signup and view all the answers

<p>Well to seismic tie = Procedure to link well formations with seismic events Wavelet estimation = Estimating wavelets at the well location Creating Low Frequency Model = Based on well logs and structural framework Quality Control = Important for input data and results at all stages</p> Signup and view all the answers

<p>Elastic properties (Acoustic Impedance, Shear Impedance, Vp/Vs ratio) = Outcome from the inversion used for interpretation Inversion Impedances = Should agree or be consistent with impedance model from well logs Single-objective functions = May become unstable due to focusing only on matching seismic data Objective of inversion = Find a simple solution matching seismic and consistent with well information</p> Signup and view all the answers

<p>Inverse problem = Reconstructing elastic parameters from seismic data Convolutional model = Representing the seismic trace as a convolution of reflectivity and wavelet Band-Limited nature of Seismic Signal = Sonic log having a broad frequency bandwidth Wavefield inversion = Finding a model that approximates the observed wave field</p> Signup and view all the answers

<p>m = Set of parameters describing the studied environment u = Wavefield corresponding to the model m prime = Model of the medium after inversion u prime = Observed wave field</p> Signup and view all the answers

<p>Inversion problem not being unique = Multiple models can generate the same wave field Inversion problem being unstable = Small data errors can cause significant perturbations in model estimate Constraints placed on inversion solution = Solution must align with a reference model derived from well data Complexity of wave propagation affecting inversion accuracy = Model only approximately describing geological environment</p> Signup and view all the answers

<p>1D horizontally layered model = Convolution of reflectivity trace and band-limited seismic wavelet Non-normal incident angles = Reflection coefficients described by Zoeppritz equations 2D and 3D models with complex boundaries = Wave field calculated as solution to complete wave equations Stacked seismic section reflections = Using equation (1) to recover P-impedance</p> Signup and view all the answers

<p>Recursive or Bandlimited approach = Transforming seismic reflection data to P-impedance Zoeppritz equations = Describing reflection coefficients for non-normal incident angles Well-known formula for reflection coefficient contrast = Determining reflection coefficients in 1D layered models Equation (1) for seismic signal inversion = Recovering P-impedance from recorded seismic signal</p> Signup and view all the answers

<p>Recursive Inversion = Reconstructing low frequencies not present in seismic data Objective Function-Based Inversion = Minimizing a specific function to find the best-fit model Seismic Reservoir Characterization = Reconstruction of elastic parameters from seismic data Band-limited Seismic Signal = Cutting off low and high frequency components</p> Signup and view all the answers

<p>Geophysics = Modern algorithms of Seismic Inversion Petroleum Exploration = Maximizing hydrocarbon recovery through production optimization Reservoir Characterization = Using seismic data to describe reservoir properties Geological Studies = Utilizing seismic inversion in studying the Earth's structure</p> Signup and view all the answers

<p>Earth Filtering Effect = Band-limiting the seismic signal Instrumentation Limitations = Partly cutting off frequency components from reflectivity Seismic Data Nature = Inability to recover low and high frequencies directly Recursive Inversion Procedure = Requiring accurate reconstruction of missing low frequencies</p> Signup and view all the answers

<p>Well Data = Accurately reconstructing low frequencies not present in seismic data Seismic Amplitudes = Describing reservoir properties for inversion purposes Dynamic Characteristics = Basis for reconstruction of elastic parameters in reservoir characterization Objective Function = Utilized by modern algorithms in minimizing to find optimal models</p> Signup and view all the answers

<p>P-impedance log = Full frequency spectrum from 0 Hz to Nyquist Seismic signal = Bandlimited by nature in the frequency domain Inverse wavelet = Applied to seismic trace by deconvolution Reflectivity trace = Converted to impedance trace</p> Signup and view all the answers

<p>Low frequencies = Usually lost by detector response or band-pass filtering circuits High frequencies = Show resolution information in the log Bandlimited seismic trace = Characterized by absence of low and high frequency information Recursive seismic inversion technique = Evolved into new generation of algorithms based on objective function minimization</p> Signup and view all the answers

<p>Model Based inversion = Includes term controlling match between observed and synthetic seismic Sparse Spike inversion = Includes various constraints on result to ensure stability and spatial coherence Geostatistical inversion methods = Generate multiple realizations of elastic properties based on well data and geostatistical variograms Neural networks approach = Approaches inversion problem from a purely mathematical point of view</p> Signup and view all the answers

<p>Band-pass filtering circuits = Eliminate low frequency noise in seismic data Deconvolution filter = Convert seismic trace to reflectivity trace Inverse wavelet filter = Convert seismic trace to reflectivity trace Recursive filter = Convert seismic trace to impedance trace</p> Signup and view all the answers

<p>Missing low frequency end of reflectivity spectrum = Complicates the inversion process Phase errors and noise contamination = Affect the observed seismic data Objective function minimization = Controls match between observed and synthetic seismic Spatial distribution of medium properties = Specified by geostatistical variograms</p> Signup and view all the answers

<p>Rock and Fluid Property Estimation = Estimate critical reservoir properties such as porosity, acoustic impedance, and fluid saturation Reservoir Connectivity and Heterogeneity = Delineate the connectivity and heterogeneity of reservoirs for optimal well placement Prospect Identification and Assessment = Identify potential hydrocarbon reservoirs and assess their size, shape, and composition Subsurface Stability Assessment = Assess the stability of subsurface structures and detect potential geohazards</p> Signup and view all the answers

<p>Reservoir Volume Estimation = Estimate the volume and reserves of hydrocarbons in a reservoir Structural Analysis = Identify subsurface structural features such as faults, folds, and fractures Monitoring and Verification = Used to monitor the injection and containment of CO2 in geological formations for CCS projects Enhanced Oil Recovery Planning = Support planning for enhanced oil recovery techniques by providing insights into reservoir properties</p> Signup and view all the answers

<p>Deterministic approaches = Allow to obtain a single optimum solution Stochastic approaches = Result in multiple realizations with the same probability PP-PS inversion = Requires additional converted PS wave data that adds independent information on shear velocity Azimuthal inversion = Uses angle gathers for a number of azimuths to estimate seismic anisotropy</p> Signup and view all the answers

<p>4D seismic studies = Used for monitoring field development and CCS projects Full stacks or seismic gathers = Can be applied with stochastic approaches based on geostatistical modeling tools Angle stacks or angle gathers = Inverted simultaneously to calculate a set of elastic properties Converted PS wave data = Adds independent information on shear velocity for PP-PS inversion</p> Signup and view all the answers