The purpose of seismic reservoir characterization is to predict the spatial distribution of the subsurface rock properties from a set of direct and indirect measurements. Commonly, rock property volumes are obtained in a two-steps approach. First, the elastic properties are inverted from seismic reflection data and then used to compute rock properties volumes by applying a calibrated rock physics models. Such an approach is not only time consuming but may also lead to biased results as the uncertainties related to seismic inversion may not be propagated through the entire geomodeling workflow. Here, we propose an iterative geostatistical shale rock physics seismic AVA inversion method to invert seismic reflection data directly for shale rock properties. The workflow consists of three main steps starting from shale properties model generation of brittleness, total organic carbon (TOC), and porosity using stochastic sequential simulation and cosimulation and calculation of a volume of shale. In the following step, elastic property volumes are calculated based on a calibrated shale rock physics model using the self-consistent approximation. The elastic models are then used for the calculation of the synthetic seismic data. In the final step, the misfit between synthetic and real data is calculated and used as part of the stochastic update of the model parameter space. The whole process is repeated until a minimum misfit between the observed and synthetic seismic is achieved. The proposed method is successfully tested on an onshore Lower Paleozoic shale gas reservoir in Northern Poland, and the predicted shale rock properties agree with those observed at a blind-well location.

/pdf/direct-geostatistical-seismic-amplitude-versus-angle-2l2kausjtp.pdf

Direct Geostatistical Seismic Amplitude Versus Angle Inversion for Shale Rock Properties

Wavefield separation via principle component analysis and deep learning in the local angle domain

Small-scale subsurface features, such as natural fractures, act as scattering sources for seismic waves propagating through the subsurface. The wavefield generated by those source points is identified as diffraction energy. The amplitude of this type of energy is much smaller than the recorded events reflected from actual interfaces between different geological layers. Moreover, diffraction energy is normally suppressed by conventional processing and standard imaging algorithms, where summations and averaging processes are applied. The common objective in such processing workflows is to focus on the high specular amplitudes in order to enhance the continuity of seismic reflection events for improving the structural mapping of the subsurface. Our goal is to complement the traditional seismic interpretation workflow by integrating information relative to diffraction energy as another seismic attribute to be interpreted.
The technique applied in this paper is based on a depth imaging algorithm that maps and bins the recorded surface information into multi-dimensional, local angle domain (LAD) common image gathers. The advantage of this system is its unique ability to decompose the wavefield into reflection and diffraction energy directly at the image locations. This paper provides a brief overview of the technology and illustrates its benefits when applied to the Eagle Ford and Barnett shale reservoirs, where seismic data can be of moderate quality, leading to accurate, high-resolution, and highcertainty seismic interpretation for risk-managed field development.

High resolution diffraction imaging for reliable interpretation of fracture systems

In this study we test brittleness prediction by integrating well and 3D seismic data using machine learning (proximal support vector machine algorithm) for the Lower Paleozoic shales from Baltic Basin in Northern Poland. The workflow allowed for differentiation of the brittle and ductile zones of the thin shale layers, as well as mapping of the marly formation (fracture barrier) with superior resolution as compared with the resolution of the original input seismic data. The important part of the success was the appropriate definition of the mineralogical brittleness index (BI) tailored to the local geological conditions. Obtained BI volume outlines both the more and less brittle zones in the lower shale unit, i.e. the Sasino formation, as well as overlaying unit with high values of BI (Prabuty marls). The mechanical BI based on Young modulus and Poisson ratio did not deliver desired brittleness characterization of the formations of interest, what confirms the weakness of estimating BI using above geomecha...

Brittleness prediction for the Lower Paleozoic shales in northern Poland

Here we show a case study of amplitude versus angle and azimuth analysis (AVAZ) applied to quantify the amount of the azimuthal anisotropy present in the Lower Paleozoic shales of the Baltic Basin (Northern Poland). The challenges encountered here are related to thin (up to 25 m), deeply buried (approximately 3 km) targets, characterized by a weak average azimuthal anisotropy (1-2% from cross-dipole sonic data). Synthetic AVAZ modelling confirms the applicability of the method. We used data after full-azimuth angle-domain pre-stack depth migration (PSDM) processed by a contractor and in-house sectored pre-stack time migration (PSTM). Application of AVAZ on full-azimuth PSDM data provided results that were further corroborated by the available calibration data. Anisotropy azimuths from AVAZ correlates with natural fracture direction from image logs (XRMI) interpretation, especially at the wells with only one dominant fracture system present. Fracture strikes inferred from AVAZ correspond also with fracture...

Seismic azimuthal anisotropy study of the Lower Paleozoic shale play in northern Poland

The exploration and development of shale plays in Europe show that the ‘statistical drilling’ approach used in some basins in recent years cannot be extend­ed to areas where local stress in rocks or fracture distribution varies both laterally and in depth. Moreover, drilling and fracturing practices confirm the presence of local geobodies resistant to hydraulic fracturing. 

This paper discusses the application of a new seismic data imaging method full-azimuth angle domain depth imaging, which is particularly useful when working with rich-azimuth seismic data. This innovative technology was applied to meet the challenges of imaging in a complex geological environ­ment, and is a pioneering solution in Polish shale gas geology. 

Results obtained in the study from the analysis of seismic data were in line with results of the geologic and geophysical analysis of the borehole data, as well as with information from microseismic monitoring of fracturing treatment. The technology delivered high-quality images of the reservoir and geomechanical characterization of rocks with the precision needed to steer horizontal drilling, detect sweet spots, and locate geobodies resistant to fracturing. 

The seismic imaging workflow is based on software spe­cifically developed to meet the challenges of shale gas seismic (Koren and Ravve, 2011, Koren et al., 2013, Canning and Malkin, 2013). One of the main advantages of this approach is that it works directly in the local angle domain (LAD) instead of the surface offset/azimuth domain. The use of in situ azimuth in LAD, visualized together with dedicated seis­mic attributes, provides information about the intensity and orientation of geological stress/fracture systems. Geothermal prospecting and seismic imaging of conventional hydrocar­bon plays can also profit from this method. This technique is particularly suitable for Poland, where conventional seismic migration of reflections from geology covered by a complex overburden has frequently resulted in improper imaging.

Imaging and characterization of a shale reservoir onshore Poland, using full-azimuth seismic depth imaging

This paper discusses the application of imaging and characterization in the local angle domain (LAD) in a shale reservoir. The system delivers high-quality images of the reservoir and geomechanical characterization of rocks with the precision needed to steer horizontal drilling, detect sweet spots, locate geobodies resistant to fracturing, or image geobodies of irregular shape. This technique is particularly attractive in Poland, where conventional seismic imaging in complex tectonics has frequently resulted in dry wells. Using this method, and combined with well data, image horizons were accurately tied to well markers, and stress/fracture orientations were highly correlated in the vicinity of the wells.

https://www.geofizyka.pl/wp-content/uploads/2015/04/First-Break-October-2014-Imaging-and-characterization-of-a-shalereservoir-onshore-Poland-using-full-azimuthseismic-depth-imaging.pdf

Imaging and Characterization of a Shale Reservoir in Onshore Poland Using Full-azimuth Seismic Depth Imaging

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Imaging and characterization of a shale reservoir onshore Poland, using full-azimuth seismic depth imaging

Imaging and Characterization of a Shale Reservoir in Onshore Poland Using Full-azimuth Seismic Depth Imaging