3-D AVO analysis and modeling applied to fracture detection in coalbed methane reservoirs

Geophysics ◽  
1997 ◽  
Vol 62 (6) ◽  
pp. 1683-1695 ◽  
Author(s):  
Antonio C. B. Ramos ◽  
Thomas L. Davis
Keyword(s):  
Poisson’S Ratio ◽  
Coalbed Methane ◽  
Spatial Location ◽  
Azimuthal Anisotropy ◽  
P Wave ◽  
Poisson's Ratio ◽  
Seismic Survey ◽  
Data Set ◽  
Avo Analysis ◽  
Coalbed Methane Reservoir

Over the years, amplitude variation with‐offset (AVO) analysis has been used successfully to predict reservoir properties and fluid contents, in some cases allowing the spatial location of gas‐water and gas‐oil contacts. In this paper, we show that a 3-D AVO technique also can be used to characterize fractured reservoirs, allowing spatial location of crack density variations. The Cedar Hill Field in the San Juan Basin, New Mexico, produces methane from the fractured coalbeds of the Fruitland Formation. The presence of fracturing is critical to methane production because of the absence of matrix permeability in the coals. To help characterize this coalbed reservoir, a 3-D, multicomponent seismic survey was acquired in this field. In this study, prestack P‐wave amplitude data from the multicomponent data set are used to delineate zones of large Poisson's ratio contrasts (or high crack densities) in the coalbed methane reservoir, while source‐receiver azimuth sorting is used to detect preferential directions of azimuthal anisotropy caused by the fracturing system of coal. Two modeling techniques (using ray tracing and reflectivity methods) predict the effects of fractured coal‐seam zones on angle‐dependent P‐wave reflectivity. Synthetic common‐midpoint (CMP) gathers are generated for a horizontally layered earth model that uses elastic parameters derived from sonic and density log measurements. Fracture density variations in coalbeds are simulated by anisotropic modeling. The large acoustic impedance contrasts associated with the sandstone‐coal interfaces dominate the P‐wave reflectivity response. They far outweigh the effects of contrasts in anisotropic parameters for the computed models. Seismic AVO analysis of nine macrobins obtained from the 3-D volume confirms model predictions. Areas with large AVO intercepts indicate low‐velocity coals, possibly related to zones of stress relief. Areas with large AVO gradients identify coal zones of large Poisson's ratio contrasts and therefore high fracture densities in the coalbed methane reservoir. The 3-D AVO product and Poisson's variation maps combine these responses, producing a picture of the reservoir that includes its degree of fracturing and its possible stress condition. Source‐receiver azimuth sorting is used to detect preferential directions of azimuthal anisotropy caused by the fracturing system of coal.

Elastic impedance parameterization and inversion with Young’s modulus and Poisson’s ratio

Geophysics ◽  
2013 ◽  
Vol 78 (6) ◽  
pp. N35-N42 ◽  
Author(s):  
Zhaoyun Zong ◽  
Xingyao Yin ◽  
Guochen Wu
Keyword(s):  
Parameter Estimation ◽  
Young’S Modulus ◽  
Seismic Data ◽  
Poisson’S Ratio ◽  
Young's Modulus ◽  
Incident Angle ◽  
P Wave ◽  
Poisson's Ratio ◽  
Data Set ◽  
Elastic Impedance

Young’s modulus and Poisson’s ratio are related to quantitative reservoir properties such as porosity, rock strength, mineral and total organic carbon content, and they can be used to infer preferential drilling locations or sweet spots. Conventionally, they are computed and estimated with a rock physics law in terms of P-wave, S-wave impedances/velocities, and density which may be directly inverted with prestack seismic data. However, the density term imbedded in Young’s modulus is difficult to estimate because it is less sensitive to seismic-amplitude variations, and the indirect way can create more uncertainty for the estimation of Young’s modulus and Poisson’s ratio. This study combines the elastic impedance equation in terms of Young’s modulus and Poisson’s ratio and elastic impedance variation with incident angle inversion to produce a stable and direct way to estimate the Young’s modulus and Poisson’s ratio, with no need for density information from prestack seismic data. We initially derive a novel elastic impedance equation in terms of Young’s modulus and Poisson’s ratio. And then, to enhance the estimation stability, we develop the elastic impedance varying with incident angle inversion with damping singular value decomposition (EVA-DSVD) method to estimate the Young’s modulus and Poisson’s ratio. This method is implemented in a two-step inversion: Elastic impedance inversion and parameter estimation. The introduction of a model constraint and DSVD algorithm in parameter estimation renders the EVA-DSVD inversion more stable. Tests on synthetic data show that the Young’s modulus and Poisson’s ratio are still estimated reasonable with moderate noise. A test on a real data set shows that the estimated results are in good agreement with the results of well interpretation.

scholarly journals New AVO Attributes and Their Applications for Facies and Hydrocarbon Prediction: A Case Study from the Northern Malay Basin

2020 ◽  
Vol 10 (21) ◽  
pp. 7786
Author(s):  
Tsara Kamilah Ridwan ◽  
Maman Hermana ◽  
Luluan Almanna Lubis ◽  
Zaky Ahmad Riyadi
Keyword(s):  
Quality Factor ◽  
Poisson’S Ratio ◽  
Water Saturation ◽  
P Wave ◽  
Poisson's Ratio ◽  
Fluid Distribution ◽  
Well Log ◽  
Log Data ◽  
Avo Analysis ◽  
Avo Attributes

Amplitude versus offset (AVO) analysis integration to well log analysis is considered one of the advanced techniques to improve the understanding of facies and fluid analysis. Generating AVO attributes are one solution to give an accurate result in facies and fluid characterization. This study is focused on a field of Northern Malay basin, which is associated with a fluvial-deltaic environment, where this system has high heterogeneity, whether it is vertically or horizontally. This research is aimed to demonstrate an application of the scale of quality factor of P-wave (SQp) and the scale of quality factor of S-wave (SQs) AVO attributes for facies and fluid types separation in field scale. These methods are supposed to be more sensitive to predict the hydrocarbons and give less ambiguity. SQp and SQs are the new AVO attributes, which derived from AVO analysis and created according to the intercept product (A) and gradient (B). These new attributes have also been compared to the common method, which is the Scaled Poisson’s Ratio attribute. By comparing with the Scaled Poisson’s Ratio attribute, SQp and SQs attributes are more accurate in determining facies and hydrocarbon. SQp and SQs AVO attributes are integrated with well log data and considered as the best technique to determine facies and fluid distribution. They are interpreted by using angle-stack seismic data based on amplitude contrast on interfaces. Well log data, e.g., density and sonic logs, are used to generate synthetic seismogram and well tie requirements. The volume of shale, volume of coal, porosity, and water saturation logs are used to identify facies and fluid in well log scale. This analysis includes AVO gradient analysis and AVO cross plot to identify the fluid class. Gassmann’s fluid substitution modeling is also generated in the well logs and AVO synthetics for in situ, pure brine, and pure gas cases. The application of the SQp and SQs attributes successfully interpreted facies and fluids distributions in the Northern Malay Basin.

Multicomponent 3-D characterization of a coalbed methane reservoir

Geophysics ◽  
1996 ◽  
Vol 61 (2) ◽  
pp. 315-330 ◽  
Author(s):  
Edward L. Shuck ◽  
Thomas L. Davis ◽  
Robert D. Benson
Keyword(s):  
Shear Wave ◽  
Seismic Data ◽  
Coalbed Methane ◽  
Accurate Determination ◽  
P Wave ◽  
Seismic Survey ◽  
Fracture Density ◽  
Structural Interpretation ◽  
Coalbed Methane Reservoir

Methane is produced from fractured coalbed reservoirs at Cedar Hill Field in the San Juan Basin. Fracturing and local stress are critical to production because of the absence of matrix permeability in the coals. Knowledge of the direction of open fractures, the degree of fracturing, reservoir pressure, and compartmentalization is required to understand the flow of fluids through the reservoir. A multicomponent 3-D seismic survey was acquired to aid in coalbed methane reservoir characterization. Coalbed reservoir heterogeneities, including isolated pressure cells, zones of increased fracture density, and variable fracture directions, have been interpreted through the analysis of the multicomponent data and integration with petrophysical and reservoir engineering studies. Strike‐slip faults, which compartmentalize the reservoir, have been identified by structural interpretation of the 3-D P‐wave seismic data. These faults form boundaries for pressure cells that have been identified by P‐wave reflection amplitude anomalies. The analysis of polarizations, traveltimes, and reflection amplitudes from the shear‐wave seismic data has allowed the identification of zones of variable fracture direction and fracture density. There is good agreement between stresses inferred from the structural interpretation and those indicated by the shear‐wave polarizations. Reflection amplitudes have been calibrated to seismic velocities and reservoir pressures through the use of petrophysical data taken from core samples. New methods have been developed for the statistical analysis of prestack shear‐wave polarizations, poststack polarizations, and the accurate determination of traveltime anisotropy. The prestack polarization analysis method allows for rapid and efficient determination of a dominant polarization direction. Shear‐wave anisotropy has been quantified over the reservoir zone using both traveltime and thin‐bed reflection response with excellent agreement between the two methods. Crack densities computed from the anisotropy show two regions of high crack density, one coinciding with a sealed overpressured cell and the other in the region of the Hamilton ♯3 well. This indicates the potential for monitoring production of coalbed methane reservoirs using multicomponent seismology.

Acoustic properties of carbonates: Effects of rock texture and implications for fluid substitution

Geophysics ◽  
2008 ◽  
Vol 73 (2) ◽  
pp. B51-B65 ◽  
Author(s):  
Klaas Verwer ◽  
Hendrik Braaksma ◽  
Jeroen A. Kenter
Keyword(s):  
Shear Modulus ◽  
Wave Velocity ◽  
Poisson’S Ratio ◽  
Acoustic Properties ◽  
P Wave ◽  
Poisson's Ratio ◽  
Fluid Substitution ◽  
Data Set ◽  
Rock Types ◽  
Rock Texture

More than 250 plugs from outcrops and three nearby boreholes in an undisturbed reef of Miocene (Tortonian) age were quantitatively analyzed for texture, mineralogy, and acoustic properties. We measured the P- and S-waves of carbonate rocks under dry (humidified) and brine-saturated conditions at [Formula: see text] effective pressure with an ultrasonic pulse transmission technique [Formula: see text]. The data set was compared with an extensive database of petrophysical measurements of a variety of rock types encountered in carbonate sedimentary sequences. Two major textural groups were distinguished on the basis of trends in plots of compressional-wave velocity versus Poisson’s ratio (a specific ratio of P-wave over S-wave velocity). In granular rocks, the framework of depositional grains is the main medium for acoustic-wave propagation; in crystalline rocks, this medium is provided by a framework of interlocking crystals formed during diagenesis. Rock textures are connected to primary depositionalparameters and a diagenetic overprint through the specific effects on Poisson’s ratio. Calculating acoustic velocities using Gassmann fluid substitution modeling approximates measured saturated velocities for 55% of the samples (3% error tolerance); however, it shows considerable errors because shear modulus changes with saturation. Introducing brine into the pore space may decrease the shear modulus of the rock by approximately [Formula: see text] or, alternatively, increase it by approximately [Formula: see text]. This change in shear modulus is coupled with the texture of the rock. In granular carbonates, the shear modulus decreases; in crystalline and cemented carbonates, it increases with saturation. The results demonstrate the intimate relationship between elastic behavior and the depositional and diagenetic properties of carbonate sedimentary rocks. The results potentially allow the direct extraction of granular and crystalline rock texture from acoustic data alone and may help predict rock types from seismic data and in wells.

P- and S-wave velocity models of shallow dry sand formations from surface wave multimodal inversion

Geophysics ◽  
2016 ◽  
Vol 81 (4) ◽  
pp. R197-R209 ◽  
Author(s):  
Paolo Bergamo ◽  
Laura Valentina Socco
Keyword(s):  
Surface Wave ◽  
Wave Velocity ◽  
Power Law ◽  
Poisson’S Ratio ◽  
Real Data ◽  
P Wave ◽  
Poisson's Ratio ◽  
S Wave ◽  
Data Set ◽  
Seismic Characterization

Surficial formations composed of loose, dry granular materials constitute a challenging target for seismic characterization. They exhibit a peculiar seismic behavior, characterized by a nonlinear seismic velocity gradient with depth that follows a power-law relationship, which is a function of the effective stress. The P- and S-wave velocity profiles are then characterized by a power-law trend, and they can be defined by two power-law exponents [Formula: see text] and two power-law coefficients [Formula: see text]. In case of depth-independent Poisson’s ratio, the P-wave velocity profile can be defined using the [Formula: see text] power-law parameters and Poisson’s ratio. Because body wave investigation techniques (e.g., P-wave tomography) may perform ineffectively on such materials because of high attenuation, we addressed the potential of surface-wave method for a reliable seismic characterization of shallow formations of dry, uncompacted granular materials. We took into account the dependence of seismic wave velocity on effective pressure and performed a multimodal inversion of surface-wave data, which allowed the [Formula: see text] and [Formula: see text] profiles to be retrieved. The method requires the selection of multimodal dispersion curve points referring to surface-wave frequency components traveling within the granular media formation and their inversion for the S-wave power-law parameters and Poisson’s ratio. We have tested our method on a synthetic dispersion curve and applied it to a real data set. In both cases, the surficial layer was made of loose dry sand. The test on the synthetic data set confirmed the reliability of the proposed procedure because the thickness and the [Formula: see text], [Formula: see text] profiles of the sand layer were correctly estimated. For the real data, the outcomes were validated by other geophysical measurements conducted at the same site and they were in agreement with similar studies regarding loose sand formations.

Some numerical solutions for Lamb's problem

1974 ◽  
Vol 64 (2) ◽  
pp. 473-491
Author(s):  
Harold M. Mooney
Keyword(s):  
Rayleigh Wave ◽  
Poisson’S Ratio ◽  
Pulse Width ◽  
Numerical Solutions ◽  
Pulse Height ◽  
P Wave ◽  
Poisson's Ratio ◽  
Wave Form ◽  
Lamb’S Problem ◽  
Wave Forms

abstract We consider a version of Lamb's Problem in which a vertical time-dependent point force acts on the surface of a uniform half-space. The resulting surface disturbance is computed as vertical and horizontal components of displacement, particle velocity, acceleration, and strain. The goal is to provide numerical solutions appropriate to a comparison with observed wave forms produced by impacts onto granite and onto soil. Solutions for step- and delta-function sources are not physically realistic but represent limiting cases. They show a clear P arrival (larger on horizontal than vertical components) and an obscure S arrival. The Rayleigh pulse includes a singularity at the theoretical arrival time. All of the energy buildup appears on the vertical components and all of the energy decay, on the horizontal components. The effects of Poisson's ratio upon vertical displacements for a step-function source are shown. For fixed shear velocity, an increase of Poisson's ratio produces a P pulse which is larger, faster, and more gradually emergent, an S pulse with more clear-cut beginning, and a much narrower Rayleigh pulse. For a source-time function given by cos2(πt/T), −T/2 ≦ T/2, a × 10 reduction in pulse width at fixed pulse height yields an increase in P and Rayleigh-wave amplitudes by factors of 1, 10, and 100 for displacement, velocity and strain, and acceleration, respectively. The observed wave forms appear somewhat oscillatory, with widths proportional to the source pulse width. The Rayleigh pulse appears as emergent positive on vertical components and as sharp negative on horizontal components. We show a theoretical seismic profile for granite, with source pulse width of 10 µsec and detectors at 10, 20, 30, 40, and 50 cm. Pulse amplitude decays as r−1 for P wave and r−12 for Rayleigh wave. Pulse width broadens slightly with distance but the wave form character remains essentially unchanged.

Shear‐wave velocity and density estimation from PS-wave AVO analysis: Application to an OBS dataset from the North Sea

Geophysics ◽  
2000 ◽  
Vol 65 (5) ◽  
pp. 1446-1454 ◽  
Author(s):  
Side Jin ◽  
G. Cambois ◽  
C. Vuillermoz
Keyword(s):  
Wave Velocity ◽  
North Sea ◽  
Random Noise ◽  
P Wave ◽  
S Wave ◽  
Data Set ◽  
Avo Analysis ◽  
The North ◽  
Avo Inversion ◽  
The North Sea

S-wave velocity and density information is crucial for hydrocarbon detection, because they help in the discrimination of pore filling fluids. Unfortunately, these two parameters cannot be accurately resolved from conventional P-wave marine data. Recent developments in ocean‐bottom seismic (OBS) technology make it possible to acquire high quality S-wave data in marine environments. The use of (S)-waves for amplitude variation with offset (AVO) analysis can give better estimates of S-wave velocity and density contrasts. Like P-wave AVO, S-wave AVO is sensitive to various types of noise. We investigate numerically and analytically the sensitivity of AVO inversion to random noise and errors in angles of incidence. Synthetic examples show that random noise and angle errors can strongly bias the parameter estimation. The use of singular value decomposition offers a simple stabilization scheme to solve for the elastic parameters. The AVO inversion is applied to an OBS data set from the North Sea. Special prestack processing techniques are required for the success of S-wave AVO inversion. The derived S-wave velocity and density contrasts help in detecting the fluid contacts and delineating the extent of the reservoir sand.

Survey design for coal-scale 3D-PS seismic reflection

Geophysics ◽  
2016 ◽  
Vol 81 (6) ◽  
pp. P57-P70 ◽  
Author(s):  
Shaun Strong ◽  
Steve Hearn
Keyword(s):  
Survey Design ◽  
High Amplitude ◽  
Azimuthal Anisotropy ◽  
Mine Planning ◽  
P Wave ◽  
Depth Range ◽  
Low Velocity ◽  
Converted Wave ◽  
Data Set ◽  
Economic Considerations

Survey design for converted-wave (PS) reflection is more complicated than for standard P-wave surveys, due to raypath asymmetry and increased possibility of phase distortion. Coal-scale PS surveys (depth [Formula: see text]) require particular consideration, partly due to the particular physical properties of the target (low density and low velocity). Finite-difference modeling provides a pragmatic evaluation of the likely distortion due to inclusion of postcritical reflections. If the offset range is carefully chosen, then it may be possible to incorporate high-amplitude postcritical reflections without seriously degrading the resolution in the stack. Offsets of up to three times target depth may in some cases be usable, with appropriate quality control at the data-processing stage. This means that the PS survey design may need to handle raypaths that are highly asymmetrical and that are very sensitive to assumed velocities. A 3D-PS design was used for a particular coal survey with the target in the depth range of 85–140 m. The objectives were acceptable fold balance between bins and relatively smooth distribution of offset and azimuth within bins. These parameters are relatively robust for the P-wave design, but much more sensitive for the case of PS. Reduction of the source density is more acceptable than reduction of the receiver density, particularly in terms of the offset-azimuth distribution. This is a fortuitous observation in that it improves the economics of a dynamite source, which is desirable for high-resolution coal-mine planning. The final-survey design necessarily allows for logistical and economic considerations, which implies some technical compromise. However, good fold, offset, and azimuth distributions are achieved across the survey area, yielding a data set suitable for meaningful analysis of P and S azimuthal anisotropy.

Seismic Survey Across An Environment With Very High Poisson’S Ratio

1999 ◽  
Author(s):  
Michael Roth ◽  
Roman Spitzer ◽  
Frank Nitsche
Keyword(s):  
Poisson’S Ratio ◽  
Poisson's Ratio ◽  
Seismic Survey ◽  
Very High

Frame moduli of unconsolidated sands and sandstones

Geophysics ◽  
1994 ◽  
Vol 59 (9) ◽  
pp. 1352-1361 ◽  
Author(s):  
James W. Spencer ◽  
Michael E. Cates ◽  
Don D. Thompson
Keyword(s):  
Poisson’S Ratio ◽  
Empirical Relation ◽  
Ultrasonic Pulse Velocity ◽  
Ultrasonic Pulse ◽  
Pulse Velocity ◽  
P Wave ◽  
Poisson's Ratio ◽  
Unconsolidated Sands ◽  
Seismic Amplitude ◽  
Seismic Frequencies

In this study, we investigate the elastic moduli of the empty grain framework (the “frame” moduli) in unconsolidated sands and consolidated sandstones. The work was done to improve the interpretation of seismic amplitude anomalies and amplitude variations with offset (AVO) associated with hydrocarbon reservoirs. We developed a laboratory apparatus to measure the frame Poisson’s ratio and Young’s modulus of unconsolidated sands at seismic frequencies (0.2 to 155 Hz) in samples approximately 11 cm long. We used ultrasonic pulse velocity measurements to measure the frame moduli of consolidated sandstones. We found that the correlation coefficient between the frame Poisson’s ratio [Formula: see text] and the mineral Poisson’s ratio [Formula: see text] is 0.84 in consolidated sandstones and only 0.28 in unconsolidated sands. The range of [Formula: see text] values in unconsolidated sands is 0.115 to 0.237 (mean = 0.187, standard deviation = 0.030), and [Formula: see text] cannot be estimated without core or log analyses. Frame moduli analyses of core samples can be used to calibrate the interpretation of seismic amplitude anomalies and AVO effects. For use in areas without core or log analyses, we developed an empirical relation that can be used to estimate [Formula: see text] in unconsolidated sands and sandstones from [Formula: see text] and the frame P‐wave modulus.

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