AVO inversion of multicomponent data for P and S impedance

2013

Simulation of acoustic impedance images by stochastic inversion of post-stack seismic reflection amplitudes and well data, Journal of Petroleum Science and Engineering,

GEOPHYSICS, 2004

The normal-incidence elastic compressional reflection coefficient admits an exact, simple expression in terms of the acoustic impedance, namely, the product of the Pwave velocity and density, at both sides of the interface. With slight modifications a similar expression can, also exactly, express the oblique-incidence acoustic reflection coefficient. A severe limitation on the use of the above two reflection coefficients in analyzing seismic reflection data is that they provide no information on shear-wave velocities that refer to the interface. In this paper, we address the natural question of whether a suitable impedance concept can be introduced for which arbitrary P-P reflection coefficients can be expressed in an analogous form as their counterpart acoustic ones. We formulate this problem by considering the mathematical conditions to be satisfied by such a general impedance function. Although no closed-form exact solution exists, our analysis provides a general framework for which, under suitable restrictions of the medium parameters, possible impedance functions can be derived. In particular, the well-established concept of elastic impedance and the recently introduced concept of reflection impedance can be better understood. Concerning these two impedances, we examine their potential for modelling and for the estimation of the AVO indicators of intercept and gradient. For typical synthetical examples, we show that the reflection impedance formulation provides consistently better results than those obtained using the elastic impedance.

GEOPHYSICS, 2009

The seismic-impedance inversion problem is underconstrained inherently and does not allow the use of rigorous joint inversion. In the absence of a true inverse, a reliable solution free from subjective parameters can be obtained by defining a set of physical constraints that should be satisfied by the resulting images. A method for constructing synthetic logs is proposed that explicitly and accurately satisfies (1) the convolutional equation, (2) time-depth constraints of the seismic data, (3) a background low-frequency model from logs or seismic/geologic interpretation, and (4) spectral amplitudes and geostatistical information from spatially interpolated well logs. The resulting synthetic log sections or volumes are interpretable in standard ways. Unlike broadly used joint-inversion algorithms, the method contains no subjectively selected user parameters, utilizes the log data more completely, and assesses intermediate results. The procedure is simple and tolerant to noise, and it...

Earth Sciences Research Journal, 2018

Elastic impedance inversion is the latest development in the field of hydrocarbon exploration and production. The present research focuses on the improvement of the use of elastic impedance inversion, easing exploration of hydrocarbons. The seismic velocities change with variation in geological constraints. Constant K, which is S-wave to P-wave ratio of the nth layer and n+1 layer across the interface, it must be changed accordingly. This research focuses on testing the effects of K as a constant in the elastic impedance equation. As using the same value of K for all types of formations can give rise to severe errors in the interpretation of data. The importance of the value of K for particular Amplitude Variation with Offset AVO type (I-IV) is studied using different Elastic Impedance Equations. The Reflection Coefficient (RC) curves for each AVO class are generated using Zoeppritz approximation and Elastic Impedance equations. The comparison of RC curves shows significant variations at far offsets in each AVO type using the Constant value of K. When K Calculated is used, AVO type I and Type II shows a good match at near, mid and far offsets. Type III does not change due to the changing value of K. Type IV gives good agreement at near and intermediate offsets. This variation in curves, with the change in the value of K, indicates that it is a significant factor of interpretation using elastic impedance. The application of findings on well logs has given a satisfactory confirmation of the present results. This research can be helpful to resolve severe errors in the interpretation due to the constant value of K.

Journal of Petroleum Science and Engineering, 2010

Impedance inversion from petrophysics Acoustic impedance; is a key parameter for seismic and direct geologic interpretation and for detecting lateral lithologic variation; can be defined as the product of density and velocity, in the absence of density data or if the well suffers from rough hole condition and/or irregularities, another approach to determine such important parameter must be used. This paper aims to introduce an empirical relationship for estimating Z (acoustic impedance) using sonic, neutron, gamma ray data and shale, fluid and matrix densities, which is usually available in most wells. This formula depends mainly upon the density response equation and the elastic definition of the impedance. Test and application of the suggested approach in two different wells located in the Gulf of Suez basin in Egypt and in Williston Basin, USA indicates the reliability of proposed formula to calculate such parameters with very high degree of accuracy.

The Gabus Formation is a producing reservoir in the Lapang Field, West Natuna Basin, Indonesia. The reservoir consists of inter-bedded sandstones and claystones deposited in a delta front environment. The sandstone reservoir thicknesses are below seismic tuning and hence challenging to interpret.

First International Meeting for Applied Geoscience & Energy Expanded Abstracts

Joint pre-stack inversion of PP-and PS-wave data is shown to significantly improve estimation of in particular Simpedance but also P-impedance and density. For reservoir characterization, improvements in these parameters can better identify reservoir rock and fluid properties. For reservoir monitoring, time-lapse changes in P-impedance, Simpedance and density can lead to more accurate inversion of saturation and pressure changes. These claims are first demonstrated on synthetic data, and later the value is shown on onshore and offshore field projects. Joint inversion of PPand PS-wave data requires a higher level of care compared to PP-waves alone since the two wave-modes need to be acquired, processed and merged properly. This has diminished the use of PS-waves in the past. However, modern acquisition and processing on land and offshore data make this technology quantitatively more accurate and realizable. It is shown that joint inversion can lead to a larger chance of success in placing exploration and development wells.

Journal of Geophysical Research, 1989

The theory of a direct inversion method to obtain the P and S wave seismic velocities and the density of a horizontally, finely layered elastic medium from vertical and horizontal component plane wave seismograms in the tau-p (slant stacked) domain has been developed. The method is based on the downward continuation method of Bube and Burridge (1983), but plane wave seismograms with a range of ray parameters are used simultaneously to obtain the velocity and density profiles. A corrected acoustic approximation of the elastic case has also been developed with which one may obtain a model of the P wave velocity and density from vertical component seismic recordings. However, it requires the S wave velocity to be estimated a priori, for instance as a fixed fraction of the P wave velocity. Many direct inverse methods, including the Bube and Burridge procedure followed here, may lack stability when implemented numerically, specially when they are applied to real data which necessarily are band limited at both low and high frequencies.

2017

Estimation of the low frequency part of the acoustic impedance is an essential yet challenging tasks for quantitative interpretation from seismic data which is essentially band-limited in nature. Ghosh and Mandal (2016) had devised an effective solution using first principles only and demonstrated its efficacy through synthetic examples. Now in the present paper, we illustrate the method’s success on real data, thus, corroborating the internal consistency of the basic approach. The present work also establishes that the effective reconstruction of broad and smooth impedance profile is possible from first principles and band-limited field data. The main features of this work is demonstrating the ability to reconstruct an approximate impedance profile without the aid of an initial model or statistical assumption on the reflectivity series. The approximate impedance profile can serve as reliable initial input for more refined inversion or geologic interpretation.

2011

Summary Deconvolution with minimum phase wavelet assumption leaves the data with spurious phase. The phase correction required to remove the spurious phase can be done by a simple parameterization of the underlying mixed phase wavelet. The simple parameterization involves estimation of all-pass operator coefficients via cumulant matching technique. The 4 th order cumulant of the whitened data (data after removal of the minimum phase wavelet) and the 4 th order moment of the all-pass operator are matched by updating the allpass operator coefficients. Since this is a blind deconvolution problem, the shape of the cost function is unknown. Hence the optimization is performed by simulated annealing algorithm (an optimization procedure that has the ability to “jump out” of local minima and proceed towards the global minimum). The optimized coefficients of the all-pass operator is convolved with the minimum phase wavelet to estimate the mixed phase wavelet. The case study involves estimati...