PS Inversion Research Articles

Quadratic reflectivity-based joint PP and PS inversion for VTI media using the stiffness matrix

Quadratic reflectivity-based joint PP and PS inversion for VTI media using the stiffness matrix

The added value of joint PP–PS inversion for reservoir characterization: A case study using Jubarte PRM seismic data (offshore Brazil)

ABSTRACTThe added value of the joint pre‐stack inversion of PP (incident P‐wave and reflected P‐wave) and PS (incident P‐wave and reflected S‐wave) seismic data for the time‐lapse application is shown. We focus on the application of this technique to the time‐lapse (four‐dimensional) multicomponent Jubarte field permanent reservoir monitoring seismic data. The joint inversion results are less sensitive to noise in the input data and show a better match with the rock physics models calibrated for the field. Further, joint inversion improves S‐impedance estimates and provides a more robust quantitative interpretation, allowing enhanced differentiation between pore pressure and fluid saturation changes, which will be extremely useful for reservoir management.Small changes in reservoir properties are expected in the short time between the time‐lapse seismic acquisitions used in the Jubarte project (only 1 year apart). The attempt to recover subtle fourth‐dimensional effects via elastic inversion is recurrent in reservoir characterization projects, either due to the small sensitivity of the reservoirs to fluid and pressure changes or the short interval between the acquisitions. Therefore, looking for methodologies that minimize the uncertainty of fourth‐dimensional inversion outputs is of fundamental importance. Here, we also show the differences between PP only and joint PP–PS inversion workflows and parameterizations that can be applied in other projects. We show the impact of using multicomponent data as input for elastic seismic inversions in the analysis of the time‐lapse differences of the elastic properties. The larger investment in the acquisition and processing of multicomponent seismic data is shown to be justified by the improved results from the fourth‐dimensional joint inversion.

Joint PP and PS pre-stack AVA inversion for VTI medium based on the exact Graebner equation

Unconventional hydrocarbon reservoirs, such as shale rocks, are generally transversely isotropic with a vertical axis of symmetry (VTI). The identification of sweet spots in these reservoirs, which must take into account this anisotropic character, can be performed with amplitude variations with offset/angle (AVO/AVA) inversion. However, most approaches use the Rüger reflection approximate equation as forward modeling, which has low accuracy at moderate to large angles, where the seismic gathers contain most of useful information on anisotropy parameters. In this paper, we propose an exact-equation-based seismic pre-stack AVA inversion for stable estimations of anisotropy parameters in VTI media. A linear inversion scheme is adopted to save computational time and the Fréchet derivatives, the key factors of the scheme, are derived here. To improve the stability and accuracy, the PP data inversion is extended to joint PP and PS inversion, termed joint exact-Graebner-based prestack inversion (JEGI). It is applied to both synthetic and field multi-component seismic data, showing its feasibility and effectiveness.

Elastic modulus extraction based on generalized pre-stack PP–PS joint linear inversion

Joint PP–PS inversion offers better accuracy and resolution than conventional P-wave inversion. P- and S-wave elastic moduli determined through data inversions are key parameters for reservoir evaluation and fluid characterization. In this paper, starting with the exact Zoeppritz equation that relates P- and S-wave moduli, a coefficient that describes the reflections of P- and converted waves is established. This method effectively avoids error introduced by approximations or indirect calculations, thus improving the accuracy of the inversion results. Considering that the inversion problem is ill-posed and that the forward operator is nonlinear, prior constraints on the model parameters and modified low-frequency constraints are also introduced to the objective function to make the problem more tractable. This modified objective function is solved over many iterations to continuously optimize the background values of the velocity ratio, which increases the stability of the inversion process. Tests of various models show that the method effectively improves the accuracy and stability of extracting P and S-wave moduli from underdetermined data. This method can be applied to provide inferences for reservoir exploration and fluid extraction.

Generalized linear joint PP–PS inversion based on two constraints

Conventional joint PP—PS inversion is based on approximations of the Zoeppritz equations and assumes constant VP/VS; therefore, the inversion precision and stability cannot satisfy current exploration requirements. We propose a joint PP—PS inversion method based on the exact Zoeppritz equations that combines Bayesian statistics and generalized linear inversion. A forward model based on the exact Zoeppritz equations is built to minimize the error of the approximations in the large-angle data, the prior distribution of the model parameters is added as a regularization item to decrease the ill-posed nature of the inversion, low-frequency constraints are introduced to stabilize the low-frequency data and improve robustness, and a fast algorithm is used to solve the objective function while minimizing the computational load. The proposed method has superior antinoising properties and well reproduces real data.

Synthesis and Characterization of a New Series of Paramagnetic Ferroelectric Liquid Crystalline Nitroxide Radicals

A new series of all-organic liquid-crystalline (LC) chiral radical compounds, trans-1-alkoxyphenyl-4-[(4-(4-alkoxyphenyl)-2,5-dimethylpyrrolidine-1-oxy-2-yl)-benzylideneamino]benzenes (1) with various alkyl chains, containing a chiral nitroxide unit in the mesogen core were synthesized and their LC properties were fully characterized. The enantiomerically enriched compounds (2S,5S)-1 showed N*, TGBA*, SmA* and SmC* phases, while the racemates (±)-1 exhibited N, SmA and SmC phases. The phase transition behavior and the ferroelectric properties of the SmC* phase of (2S,5S)-1 differed from those of previously reported analogues with an ester group as a substitute for the imino group of (2S,5S)-1. Some of the (2S,5S)-1 series showed a temperature-dependent spontaneous polarization PS (θ) inversion. We discuss the origin of this difference in terms of their molecular structures optimized by molecular orbital calculations. The phase transition behavior supports the hypothesis that the large ϕ, which is defined as the angle between the molecular long axis (one of the principal axes of inertia) and the direction of the dipole moment in each molecule, results in the stabilization of the SmA* (SmA) phase.

Application of joint PP and PS inversion to the exploration of shale-gas reservoirs

In recent years,the development of shale oil and gas shows that shale heterogeneity and lateral orientation have relatively great impacts on single well shale gas production,recovery factor and the economy of shale gas exploitation,and natural micro-fracture is the main factor resulting in shale heterogeneity. Accordingly,to carry out research on the natural micro-fractures and prediction of sweet spots within shale has become an inevitable choice for successful emplacement of high-yielding wells and improving economic benefits of shale gas exploitation. Based on the high resolution 3C /3D seismic data in Marcellus shale play within Appalachian Basin,North America,natural micro-fracture zone of Marcellus shale was predicted by means of fast and slow converted shear wave( PSV-1 / PSV-2) integrated interpretation,then the open / closed fractures and gas-bearing property of extensional micro-fractures were separately identified and detected by utilizing combined attribute parameters like joint inversion density,velocity ratio of compressional and converted wave( vP/ vS) extracted from joint inversion of compressional wave and converted shear wave( PP-PS). In addition,drilling data were used to verify the sweet spots predicted by geophysical method in Marcellus shale. Joint inversion technique( PP-PS) has outstanding advantages in natural extensional micro-fractures identification and gas-bearing detection,which can effectively reduce the drilling risk.

From ocean-bottom cable seismic to porosity volume: A prestack PP and PS analysis of a turbidite reservoir, deepwater Campos Basin, Brazil

The Campos Basin is the best known and most productive of the Brazilian coastal basins. Turbidites are, by far, the main hydrocarbon-bearing reservoirs in the Campos Basin. Using a 4C ocean-bottom cable seismic survey, we set out to improve the reservoir characterization in a deepwater turbidite field in the Campos Basin. To achieve our goal, prestack angle gathers were derived and PP and PS inversion were performed. The inversion was used as an input to predict the petrophysical properties of the reservoir. Converting seismic reflection amplitudes into impedance profiles not only maximizes vertical resolution but also minimizes tuning effects. Mapping the porosity is extremely important in the development of hydrocarbon reservoirs. Combining seismic attributes derived from the PP and PS multicomponent data and porosity logs, we used linear multiregression and neural networking to predict porosity between the seismic attributes and porosity logs at the well locations. After estimating porosity in the well locations, those relationships were applied to the seismic attributes to generate a 3D porosity volume. The porosity volume highlighted the best reservoir facies in the reservoir. The integration of elastic impedance, shear impedance, and porosity improved the reservoir characterization.

Joint PP and PS AVO inversion based on Zoeppritz equations

Considering Zoeppritz equations, reflections of PP and PS are only the function of ratios of density and velocity. So the inversion results will be the same if the ratios are the same but values of density, velocities of P-wave and S-wave are different without strict constraint. This paper makes efforts to explore nonlinear simultaneous PP and PS inversion with expectation to reduce the ambiguity of AVO analysis by utilizing the redundancy of multi-component AVO measurements. Accurate estimation of ratio parameters depends on independence of input data. There are only two independent AVO attributes for PP reflectivity (i.e. intercept and gradient) and two for PS reflectivity (i.e. pseudo-intercept and pseudo-gradient or extreme amplitude), respectively. For individual PP and PS inversion, the values of least-squares objective function do not converge around a large neighborhood of chosen true model parameters. Fortunately for joint PP and PS inversion the values of the least-squares objective function show closed contours with single minima. Finally the power function fitting is used to provide a higher precision AVO attributes than traditional polynomial fitting. By using the four independent fitting attributes (two independent attributes for PP and PS respectively), the inversion of four ratio parameters (velocities and densities) would be estimated with less errors than that in traditional method.

Delineating oil-sand reservoirs with high-resolution PP/PS processing and joint inversion in the Junggar Basin, Northwest China

Dramatic lateral lithological variations in the fluvial sediments in Chepaizi, in the Junggar Basin of Northwest China, have posed challenges in distinguishing true and false “bright spots” in oil-bearing sand reservoirs. A high-resolution multicomponent seismic survey and joint prestack PP and PS inversion conducted recently provided an effective technique for solving the problem and successfully delineating the characteristics of the reservoir. This is due to the different reflection response of shear waves to the lithology and fluid content, and their ability to resolve thin layers. Surface-consistent amplitude- and resolution-preserving pro-cessing produced high-quality prestack PP and PS migrated gathers and stacks for extracting seismic attributes. Application of joint prestack PP and PS inversion resulted in higher fluid factors and lower [Formula: see text] in oil-bearing sands compared with dry sands. The correlation between the inversion and the existing well data suggests that high-resolution multicomponent AVO can reduce drilling risks and provide more accurate reservoir characterization.

Prediction of Shale Plugs between Wells in Heavy Oil Sands using Seismic Attributes

A fundamental geologic problem in the Steam-Assisted Gravity Drainage (SAGD) heavy oil developments in the McMurray Formation of Northern Alberta is to determine the location of shales in the reservoirs that may interfere with the steaming or recovery process. Petrophysical analysis shows that a key acoustic indicator of the presence of shale is bulk density. In theory, density can be derived from seismic data using Amplitude Versus Offset (AVO) analysis of conventional or multicomponent seismic data, but this is not widely accepted in practice. However, with billions of dollars slated for SAGD developments in the upcoming years, this technology warrants further investigation. In addition, many attributes can be investigated using modern tools like neural networks; so, the density extracted from seismic using AVO can be compared and combined with more conventional attributes in solving this problem. Density AVO attributes are extracted and correlated with “density synthetics” created from the logs just as the seismic stack correlates to conventional synthetics. However, multiattribute tests show that more than density is required to best predict the volume proportion of shale (Vsh). Vsh estimates are generated by passing seismic attributes derived from conventional PP, and multicomponent PS seismic, AVO and inversion from an arbitrary line following the pilot SAGD wells through a neural network. This estimate shows good correlation to shale proportions estimated from core. The results have encouraged the application of the method to the entire 3D.

Psinversion in three homologous series of ferroelectric 5-(2-fluoro-alkyloxy)-2-(4-n-alkylphenyl) pyrimidines

Abstract We synthesized members of four homologous series of the general formula Most of the compounds exhibit smectic phases with negative PS, at higher temperatures, changing the sign to give positive PS, at lower temperatures. The inversion temperatures and PS, at a reduced temperature show alternating behavior. The tilt angles measured by X-rays as well as by electrooptical investigation do not possess any anomaly at TPS, and in several cases are practically constant. We discuss the molecular arrangemeit in C and C* phases. In order to explain the PS behavior we use the molecular statistical theory developed by Osipov et al. In this theory Ps is determined by the chiral dipole, the steric dipole and the polarizability properties of the molecules; the interplay of these properties characterizes the binding site. By opposite signs of dipolar and quadrupolar coupling of the molecules and the temperature dependence of the steric dipoles, the Ps inversion can be explained.