Instantaneous Seismic Attributes Research Articles

Unsupervised machine learning for time-lapse seismic studies and reservoir monitoring

Time-lapse (4D) seismic analysis plays a vital role in reservoir management and reservoir simulation model updates. However, 4D seismic data are subject to interference and tuning effects. Being able to resolve and monitor thin reservoirs of different quality can aid in optimizing infill drilling or in locating bypassed hydrocarbons. Using 4D seismic data from the Maui field in the offshore Taranaki Basin of New Zealand, we generate typical seismic attributes sensitive to reservoir thickness and rock properties. We find that spectral instantaneous attributes extracted from time-lapse seismic data illuminate more detailed reservoir features compared with those same attributes computed on broadband seismic data. We have developed an unsupervised machine-learning workflow that enables us to combine eight spectral instantaneous seismic attributes into single classification volumes for the baseline and monitor surveys using self-organizing maps (SOMs). Changes in the SOM natural clusters between the baseline and monitor surveys suggest production-related changes that are caused primarily by water replacing gas as the reservoir is being swept under a strong water drive. The classification volumes also facilitate monitoring water saturation changes within thin reservoirs (ranging from very good to poor quality) as well as illuminating thin baffles. Thus, these SOM classification volumes indicate internal reservoir heterogeneity that can be incorporated into reservoir simulation models. Using meaningful SOM clusters, geobodies are generated for the baseline and monitor SOM classifications. The recoverable gas reserves for those geobodies are then computed and compared with production data. The SOM classifications of the Maui 4D seismic data seem to be sensitive to water saturation change and subtle pressure depletions due to gas production under a strong water drive.

The Integrated Approach to Seismic Attributes of Lithological Characterization of Reservoirs: Case of the F3 Block, North Sea-Dutch Sector

Technological development, particularly the development of signal processing, has contributed to the improvement of the quality of results in the analysis of the characteristics of hydrocarbon reservoirs. This scientific advance is especially marked by the introduction of seismic attributes in the characterization of reservoirs. This paper is aimed at evaluating the contribution of seismic attributes in the lithological characterization of hydrocarbon accumulation zones. Thus, it has been found that instantaneous attributes make it possible to highlight the different properties of reservoir rocks. Techniques for extracting three-dimensional volume attributes have been applied to a 3D seismic data volume of the F3 block in the Dutch sector of the North Sea. The purpose of using these volume attributes is to extract signal characteristics from lithofacies in hydrocarbon zones. The results provide a remarkable contribution to instantaneous seismic attributes in reservoir location, hydrocarbon detection, and reservoir lithological prediction. The instantaneous amplitude, the derivative of amplitude 1, the factor Q, the energy and the Hilbert transform are attributes which highlight the presence of hydrocarbons through the bright spots. Thus, curvature, similarity, dip, and coherence are useful in the determination of traps such as faults and anticlines. The crossing of the instantaneous amplitude and the instantaneous frequency makes it possible to analyze the lithofacies. In the same way, the analysis of the crossed diagrams between the porosity and the instantaneous amplitude made it possible to define the different layers of the reservoir.

Multichannel Complex Seismic Traces Analysis

Instantaneous seismic attributes are commonly used in assisting seismic interpretation and stratigraphy analysis. We compute the instantaneous seismic attributes using 1-D seismic traces and the corresponding quadrature (Hilbert transformed) traces. However, the 1-D seismic trace and the corresponding quadrature trace are sensitive to noise and seismic processing artifacts. To improve the lateral continuity of instantaneous seismic attributes, we propose to compute instantaneous attributes using multichannel seismic traces. Dynamic time warping (DTW) is used to align the seismic traces centered at the analysis point which mitigates the effect of structure dip on the multichannel complex seismic trace analysis (MCSTA). We fine interpolate the 1-D seismic traces to minimize the possible error in the computation of the error matrix of DTW. We also define a constraint in the backtracking of DTW to avoid severe strain (stretch or squeeze) between seismic traces. We obtain the “robust” 1-D complex seismic trace by applying Gaussian smoothing to the aligned complex seismic traces. We finally obtain instantaneous seismic attributes from the smoothed 1-D seismic trace and the corresponding quadrature trace. We show the superiority of new instantaneous attributes by applying our method to real seismic data.

Validated artificial neural networks in determining petrophysical properties: A case study from Colombia

We have applied instantaneous seismic attributes to a stacked P-wave reflected seismic section in the Tenerife field located in the Middle Magdalena Valley Basin in Colombia to estimate the volume of clay [Formula: see text] and the density [Formula: see text] at seismic scale. The well logs and the seismic attributes associated to the seismic trace closer to one of the available wells (Tenerife-2) is the information used to train some multilayered artificial neural networks (ANN). We perform data analysis via the gamma test, a mathematically nonparametric nonlinear smooth modeling tool, to choose the best input combination of seismic attributes to train ANNs to estimate [Formula: see text] and [Formula: see text]. Once the ANNs are trained, they are applied to predict these parameters along the seismic line. From the continuous estimations of [Formula: see text], we distinguish two facies: sands for [Formula: see text] and shales when [Formula: see text]. These estimations confirm the production of the Mugrosa C-Sands zone, and we draw the brown shale that correlates with the high-amplitude attributes and the yellow sand that correlates with the low-amplitude attributes. Using the well-log information for [Formula: see text] and the facies classification (also in the well log), two cubic polynomials that depend on time (or depth) are obtained, one for sands and the other for shales, to fit the [Formula: see text]. These two cubic polynomials and the facies classification obtained from the [Formula: see text] at the seismic scale enable us to estimate [Formula: see text] at the seismic scale. To validate the 2D [Formula: see text] and [Formula: see text] predicted data, a forward-modeling software (the Kennett reflectivity algorithm) is used. This model calculates synthetic seismograms that are compared with the real seismograms. This comparison indicates a small misfit that suggests that the [Formula: see text] and [Formula: see text] images are representing the reservoir description characteristics and the ANN method is accurate to map these parameters.

Seismic attribute analysis for fracture detection and porosity prediction: A case study from tight volcanic reservoirs, Barmer Basin, India

The Raageshwari Deep Gas Field is situated in the southern part of the onshore Barmer Basin in Rajasthan, India. The field contains gas condensate with excellent gas quality reservoired dominantly within the tight volcanic rocks. Optimal development and production of the tight reservoirs requires characterization of faults and natural fractures that are important to fluid flow and production. Reservoir quality of the volcanic complex is governed by the distribution of matrix pore spaces and fractures. Use of seismic attributes for detecting effective reservoir pore spaces such as fractured zones and vesicles is challenging considering the limits of seismic resolution in the tight volcanic reservoirs. Poststack seismic attributes used in this study for fracture detection include geometric attributes such as coherency for detection of seismically resolved faults and reflection curvature attributes for discrimination of subseismic faults. Discrete frequency components extracted from seismic data are also used to analyze geologic discontinuities. Besides geometric attributes, seismic wave attenuation from the basic instantaneous seismic attributes — instantaneous amplitude, phase, and frequency — are also key indicators of fractured zones and vesicles that create effective pore spaces. In fractured intervals within the volcanic reservoirs, a decrease in density and slowdown in acoustic propagation velocity yields a relative drop in P-wave impedance, which are important characteristics to determine fractured zones. Detected fractured zones from seismic attributes were validated with wells, image logs, and production data. In addition to fracture detection, predicting subsurface properties, such as porosity distribution away from wells, has always been a fundamental requisite for appropriate infill well planning. Full-azimuth seismic data and selected seismic attributes were used in multiattribute analysis to predict porosity and were correlated with “blind” wells. This study captures the heterogeneous volcanic rock porosity distribution in the field, improving the understanding of varied production behavior observed within the volcanic rock complex.

Noncontact Measurement and Detection of Instantaneous Seismic Attributes Based on Complementary Ensemble Empirical Mode Decomposition

Hilbert–Huang transform (HHT) is a popular method to analyze nonlinear and non-stationary data. It has been widely used in geophysical prospecting. This paper analyzes the mode mixing problems of empirical mode decomposition (EMD) and introduces the noncontact measurement and detection of instantaneous seismic attributes using complementary ensemble empirical mode decomposition (CEEMD). Numerical simulation testing indicates that the CEEMD can effectively solve the mode mixing problems of EMD and can provide stronger anti-noise ability. The decomposed results of the synthetic seismic record show that CEEMD has a better ability to decompose seismic signals. Then, CEEMD is applied to extract instantaneous seismic attributes of 3D seismic data in a real-world coal mine in Inner Mongolia, China. The detection results demonstrate that instantaneous seismic attributes extracted by CEEMD are helpful to effectively identify the undulations of the top interfaces of limestone.

Review of instantaneous, wavelet, and weighted seismic attributes along with a computational library

Complex trace analysis is the most widely used method for transforming post-stack seismic traces into a number of instantaneous seismic attributes which are used to make a variety of geological interpretations. Several useful interpretations require a combination of these attributes to be computed and displayed simultaneously which demand high performance and large memory resources. This paper reviews instantaneous, wavelet, and weighted average attributes and presents a digital signal processing library for their efficient computation by optimizing performance and memory.

Detection of the Long Period Long Duration (LPLD) Events in Time-and Frequency-Domain

Long Period Long Duration (LPLD) signals are unusual seismic events that can be observed during hydraulic fracturing. These events are very similar in appearance to tectonic tremors sequences, which were first observed in subduction zones. Their nature is not well known. LPLD might be related to the productivity of the reservoir. Different methods of the LPLD events’ detection recorded during hydraulic fracturing are presented. The author applied two methods for LPLD detection–Butterworth filtering and Continuous Wavelet Transform (CWT). Additionally, a new approach to LPLD events detection–instantaneous seismic attributes–was used, common in a classical seismic interpretation but not in microseismic monitoring.

Frequency-dependent seismic-stratigraphic and facies interpretation

In this study, seismic models and a Starfak and Tiger Shoal fields data set in the Gulf of Mexico Basin are used to investigate uncertainties caused by the frequency dependence of seismic data and solutions for avoiding pitfalls in seismic-stratigraphic and facies interpretation. Seismic amplitude and instantaneous attributes, along with stratigraphic interpretation of these attributes, are controlled by seismic interference, or tuning, between thin geologic units. Seismic-tuning effects include thickness tuning and frequency tuning, which cause nonlinear variations of reflection amplitude and instantaneous seismic attributes with thickness and/or data frequency. Seismic modeling shows that, whereas thickness tuning determines seismic-interference patterns and, therefore, occurrence of seismic events and seismic facies in layered rock, frequency tuning may further influence the nature of the correlation of seismic data and geologic time and modify seismic facies. Frequency dependence offers a new dimension of seismic data, which has not been fully used in seismic interpretation of geology. Field-data examples demonstrate that a stratigraphic formation is typically composed of lithofacies of varying thicknesses, and a broadband, stacked seismic data set is not necessarily optimal for stratigraphic and facies interpretation. Although it is difficult to predict correct frequency components for interpretation of not-yet-known geologic targets, local geologic models and well data can be used to optimize the frequency components of seismic data to a certain degree and intentionally modify seismic-interference patterns and seismic facies for better seismic interpretation of geologic surfaces, sediment-dispersal patterns, geomorphology, and sequence stratigraphy.

Seismic attribute extraction based on HHT and its application in a marine carbonate area

The Hilbert-Huang transform (HHT) is a new analysis method suitable for nonlinear and non-stationary signals. It is very appropriate to seismic signals because they show both non-stationary and nonlinear characteristics. We first introduce the realization of HHT empirical mode decomposition (EMD) and then comparatively analyze three instantaneous frequency algorithms based on intrinsic mode functions (IMF) resulting from EMD, of which one uses the average instantaneous frequency of two sample intervals having higher resolution which can determine that the signal frequency components change with time. The method is used with 3-D poststack migrated seismic data of marine carbonate strata in southern China to effectively extract the three instantaneous attributes. The instantaneous phase attributes of the second intrinsic mode functions (IMF2) better describe the reef facies of the platform margin and the IMF2 instantaneous frequency attribute has better zoning. Combining analysis of the three IMF2 instantaneous seismic attributes and drilling data can identify the distribution of sedimentary facies well.

Seismic reflection characteristics of fluvial sand and shale interbedded layers

A sedimentary geological model is established in order to study the seismic reflection characteristics of channel sand bodies. Synthetic seismic shot gathers are simulated using the acoustic wave equation and then are prestack time migrated. On the imaged data, the reflection characteristics and instantaneous attributes are analyzed and log-constrained impedance inversion is tested. Because of wave field interference, the experimental results show that seismic events do not definitely correspond to the channel sand bodies and that seismic modes of occurrence do not represent the actual ones. The seismic events formed by wave interference may lead to errors and pitfalls in sand body interpretation. The corresponding relations between instantaneous seismic attributes and sedimentary sands are not well established. Log-constrained impedance inversion improves the resolution of channel sands. However, if the inverted resolution is forced to be too high, artifacts related to the initial model may occur.

Automatic detection of interfering seismic wavelets using fractal methods

Interference of reflections from upper and lower interfaces of geological units is a common source of interpretational ambiguity. This paper utilizes the fractal dimension of instantaneous seismic attributes to study this interfering phenomenon. Using a 1D synthetic seismic trace, we examine the divider, Hurst, spectral and variance fractal methods. Since each method utilizes a moving window technique as part of its analysis, a series of optimum window lengths needs to be determined. The four methods are applied to the instantaneous amplitude, phase and frequency attributes of a series of 1D synthetic seismic traces. To study wavelet interference on 2D seismic sections, we generate four 2D synthetic seismic sections by convolving a zero phase and a minimum phase wavelet with two different wedge models. For the first model, the reflection coefficient of the upper wedge interface is positive and the lower interface negative, whereas for the second model, the polarities are positive. Our results suggest that fractal analysis of the instantaneous phase, using the Hurst method, can separate two opposite polarity wavelets within a distance of λ/16 or greater and of λ/4 or greater when they have the same polarity. Our results are not sensitive to random noise when the signal-to-noise-ratio is greater than 10.

Experimental and theoretical rock physics research with application to reservoirs, seals and fluid processes

This paper describes a range of geophysical research activities at the Australian Resources Research Centre based around the development of an experimental capability to validate theoretical and numerical modelling predictions of geophysical properties of reservoirs and seals. Laboratory tests performed on reservoir sandstones, shales and artificial sandstones under a range of controlled triaxial stress conditions allow the full anisotropic elastic tensor to be calculated from ultrasonic measurements on a single core. The analysis of elastic properties and anisotropy in relation to varied stress, pore pressure and fluid saturation can provide significant insight for both exploration (e.g. pore pressure prediction) and production (4D seismic feasibility studies for changes in pore pressure and saturation during production). Ultrasonic data from core measurements are related to seismic response through theoretical analysis of frequency effects and the methodologies developed from this research are subsequently tested on 3D seismic data. Understanding the causes and degree of anisotropy, for example, are critical for depth conversion, imaging, fluid identification (e.g. AVO) and dynamic Poisson's ratio. Velocity hysteresis observed in shales and sandstones with different stress histories has led to an improved understanding of the concept of effective stress and its effect on seismic data. Positive correlations between effective stress and pore pressure with several instantaneous seismic attributes have been established that allow direct mapping of seismic attribute changes into absolute values of effective stress. This methodology has been tested on a 3D seismic dataset from the Northwest Shelf of Australia and shows good agreement with both the distribution and magnitude of the overpressures present. Similarly, X-ray CT images have been combined with ultrasonic measurements conducted on core samples to establish the sensitivity of instantaneous seismic attributes to various degrees of fluid saturation. These results indicate that seismic attributes can be used as an alternative approach for discrimination between pressure and saturation affects. The results from these combined research activities have improved our understanding of the impact of effective stress, anisotropy and saturation on the interpretation of geophysical data, which has implications for pore pressure prediction, 4D seismic evaluations, depth conversion and stress-saturation discrimination.

Quantitative prediction methodology for differential stresses and discrimination between pressure and fluid saturation based on seismic attributes derived from experimentally recorded waveforms

A quantitative methodology for remote prediction of differential stresses is proposed, based on rock physics responses to various overpressure mechanisms. The method utilises relationships between various seismic attributes and differential pressures which were established through a series of laboratory tests. A number of ultrasonic experiments simulating normal compaction, disequilibrium compaction, fluid expansion and tectonic mechanisms of overpressure were performed on reservoir sandstone and shale core samples. The velocity changes and the effects of different stress paths on transmitted ultrasonic pulses were investigated through changes of instantaneous waveform attributes. In all measurements the dependence between seismic velocities and differential stresses coincide well with Eberhart-Phillips empirical relationship. A positive relationship between differential pressure and several instantaneous seismic attributes has been established for the first time in these experiments. Results proved that well-known empirical relationships between differential pressure and seismic velocity are also applicable for a number of seismic attributes. Similarly, based on the combined X-ray CT images and ultrasonic measurements conducted on core samples, the sensitivity of instantaneous seismic attributes to various degree of fluid saturation has been analysed. It was found that several seismic attributes exhibit, in form, similar relationships to the known theoretical models established between seismic velocities and fluid saturation. These results indicate that seismic attributes can be used as alternative approach for discrimination between changes caused by increased pore pressure and fluid saturation. This enables the prediction of differential stresses by using seismic attribute changes. The proposed methodology has been tested on a 3-D seismic dataset from the Northwest Shelf of Australia and shows good agreement with both the distribution of normally pressured and overpressured wells as well as the magnitude of the overpressures present.

Weighted average seismic attributes

Local weighted averaging of instantaneous seismic attributes improves their interpretability by removing spikes and reducing rapid and confusing variations. Averaging in a window weighted by the instantaneous power produces a local measure that equals a Fourier spectral average, facilitating quantitative analysis. Local 1-D frequency and bandwidth are scalars, but local 2-D and 3-D seismic attributes derive from average vector wavenumbers, which may require velocity information. The direction of the average vector wavenumber provides average dip and azimuth, and its magnitude provides a measure of average wavelength or frequency. A related measure of bandwidth is a scalar in all dimensions; it includes contributions from both instantaneous bandwidth and the variance of instantaneous frequency or wavenumber. It quantifies data similarity.

Instantaneous frequency: Discussion

In Properties of instantaneous seismic attributes (July 1991 TLE), R.E. White shows graphically the instantaneous frequency can be negative. This property of the instantaneous frequency is very interesting, especially when we keep in mind the fact that an analytic signal associated with a real signal contains no negative‐frequency components. White’s graph, therefore, deserves some analytical consideration.