A Professional Approach to the Study of the Earth’s Interior

Processing and interpretation of 2D and 3D seismic data

GeoGrid’s hallmark is the close cooperation and often collaboration between the groups of processing and interpretation of seismic data within the geophysical departments.

Processing of seismic data

Final results of any geological and geophysical activities in the form of geological models of prospective targets depend largely on the results of seismic data processing which, apart from the structural framework, is the foundation of the results to be obtained.

Seismic data processing and interpretation are among the core strategic activities of the GeoGrid Center. The GeoGrid seismic data processing group has both technical tools and personnel required for the full cycle of complex seismic data processing.

Processing of 2D and 3D  onshore data

The GeoGrid Center has all the tools required for both standard and custom flows of 2D and 3D onshore data processing. The standard processing flow includes kinematic (data quality assessment, geometry assignment, spherical divergence compensation, static correction evaluation, velocity analysis, etc) and dynamic (noise attenuation, multiple wave attenuation, surface consistent amplitude correction, surface consistent inverse filtering, etc.) sets of procedures. A separate stage in the classical view of the processing flow are the migration transformations which can be implemented by the GeoGrid computing facilities in pre- and post-summation modifications both in time and depth domains.

For each project an optimum flow is chosen based on customer requirements and specific geological conditions, in order to to maximize the resolution of the seismic record while preserving the true amplitude correlation to maximize the signal to noise ratio.

Processing of 2D and 3D offshore data

Offshore seismic survey data and the corresponding processing flow are somewhat different from wavefields found  onshore. This is due to offshore survey methods and the nature of registered wavefields. The key differences between offshore and onshore data are the survey geometry, an almost total absence of static corrections in offshore data, as well as differences in source and receiver characteristics.

One of the main types of noise for offshore seismic surveys are multiple reflection waves in the water, which are successfully removed by the GeoGrid via algorithms based on the Radon transform, the wave equation solved through the WEMA method, and via multiple wave model forecasting (surface-related multiple elimination, SRME).

The seismic data processing group of the GeoGrid regularly implements 2D and 3D offshore seismic data processing projects.

Interpretation of multicomponent seismic data

For a long time multicomponent data were overlooked due to their complexity and high costs. However, seismic survey encounters increasingly complex challenges (e.g. assessment of rock lithology, fracturing and direction, porosity, fluid saturation, etc.) which requires recording the whole set of the wavefield components: longitudinal (PP), converted (PS) and shear (SS) waves.

The full-wave seismic survey technology includes recording and processing of seismic data aimed to maximize the volume of geological information via the processing of rich azimuth and multicomponent data.

Engineers at the GeoGrid computational facilities have hands-on experience of multicomponent seismic data processing both onshore(3D/3C, 4D/3C, 3D/9C, 4D/9C) and in offshore and transit areas (3D/4C, 4D/4C).

4D monitoring of deposits in development

Experience of development of deposits discovered 30-40 years ago shows that, even with highly efficient production, about 50% of hydrocarbons remain not recovered. This often happens due to the closure of fractures because of the significant fall of pore pressure in the drainage area which inevitably results in fluid filtration stoppage.

One of the few solutions in this case is regular seismic re-surveying and re-comparing survey results in the course of production.

GeoGrid often acts as the hydrocarbon deposit development monitoring operator for sustainable process management.

Supervisory control over the processing

The GeoGrid Center provides supervisory support services for all processing stages performed by 3rd party organizations. This type of service is rather in-demand in recent years, because not only the contractor organization but also the supervisor company are responsible for the quality of deliverables. This significantly improves the quality of deliverables which is proved by the reference list of the projects completed.

Creating a unified database of seismic surveys from multiple years

Any geoscientist faces the problem of the joint use of seismic survey data from multiple years in his or her work. Taking into consideration the specifics of evolution of the national geological and seismic survey, the processing group of the GeoGrid Center has repeatedly faced the task of synchronous processing of data obtained by different parties and with different equipment at intervals which may make up tens of years.

The experience has shown that thorough processing of various data with due account for transformation operators can produce results which can be used for cooperative structural or sometimes even dynamic interpretation of seismic data.

Interpretation of seismic data

The GeoGrid Center provides the full range of services for structural and dynamic interpretation of seismic data.

Reliability of all interpretation procedures, both geophysical and geological, depends primarily on the thorough correlation of reflecting horizons, as well as on detailed tracing of tectonic dislocations. The experience of cooperation with many service organizations shows that this stage is often overlooked.

The GeoGrid Center’s distinctive feature is its due and special attention to the structural interpretation which necessarily includes the concurrent work of both geophysics and geologists having deep experience in studying wavefields in different areas of the world.

Building velocity-depth models

Obtaining depth properties of formations from their time surfaces for geologists, drilling technicians and developers is a rather important procedure which is however often reduced to rough estimates of velocity properties in well points. The GeoGrid Center uses velocity-depth models for mandatory comprehensive analysis of velocities obtained from seismic data, as well as velocities based on sonic scanning and VSP data in wells. Combined with time and depth data analysis based on seismics and wells, the velocity model produced is highly reliable which results in the high accuracy of resulting structural models.

Attribute analysis

The attribute analysis in comparison with the modern dynamic interpretation of seismic data recedes into the background, giving place to actively progressing methods of seismic inversion and amplitude analysis from seismographs. However, due to the fact that attribute calculation is based on the final view of the wavefield rather than on original seismographs, the process of attribute assessment is more cost-effective and more stable compared to seismograph analysis methods. Moreover, experience shows that qualitative attribute analysis can often turn into quantitative analysis for certain fields with further forecasting of formation properties. An important drawback of this method is the lack of correlation of parameters from one field to another.

Attribute analysis is a mandatory dynamic interpretation process in GeoGrid regardless of the initial goals, as it can be used for qualitative studies of dynamical properties of the area of operations.

Frequency-dependent interpretation

The GeoGrid Center has a wide experience in frequency-dependent interpretation of seismic data, implemented in spectral decomposition methodology. Using the discrete Fourier transform and continuous wavelet transform methods for young sedimentary sequences allows to trace palaeochannels, fans and other prospective geological objects at the qualitative level, which cannot be traced in the summary spectrum of the seismic record.

AVO/AVA analysis

The Amplitude Variation with Offset (AVO) analysis is studying amplitude changes with distance and is applied to data before summation. This approach is currently used mainly for prospecting and exploration of gas reservoirs in young terrigenous rocks and for finding new reserves in already developed fields. GeoGrid has vast experience of AVO analysis resulting into relevant AVO attributes: Intercept (A), Gradient (B) of the binomial Shuey approximation, the fluid factor in chalk terrigenous sediments of West Siberia and Miocene sediments of the Vietnam plate.

The petrophysical substantiation for solving seismic inversion problems

The primary goal of the petrophysical substantiation is establishing correlation relationships between elastic parameters and petrophysical properties of deposits being studies. This analysis can be used to evaluate the efficiency of inversion transforms for forecasting reservoir properties and the possibility of lithotype separation in the elastic parameter field.

To that end, all the projects related to the inverse problem of seismic data in GeoGrid include mandatory analysis of relationships between elastic (acoustic impedance, shear impedance, Poisson’s ratio, volume compression modulus, shear modulus, etc.) and petrophysical (porosity, effective depth, etc.) properties of target formations.

Seismic data inversion

Transformation of seismic wavefields into impedance stacks and cubes is the key stage of dynamic interpretation of seismic data for a number of reasons, the main of which is obtaining quantitative properties of target formations, namely acoustic (Vp*ρ) and shear (Vs*ρ) impedances. These attributes are petrophysical properties of a rock and can be confirmed via measurements in wells.

The GeoGrid Center has all the tools required for any type of acoustic (recursive, operator-based, rare pulses, based model) and elastic (extended elastic, synchronous) inversions.

Prediction of petrophysical properties and of target formations

The quality of seismic data can now be used to predict lithology and fracturing, determine the type of formation fluid, evaluate porosity and pore pressure.

The comprehensive approach to determining petrophysical properties of target formations based on joint qualitative (attribute analysis, spectral decomposition, etc.) and quantitative (rock physics modelling, seismic inversion) types of analysis can be used to produce highly accurate predictions of desired parameters, confirmed by results of deep drilling.

Comprehensive interpretation of geophysical data

The seismic surveying method is often incapable of solving the relevant problems due to certain geological and technical obstructions. Other geophysical methods of the Earth's crust exploration should be used in such cases.

Engineers of the geophysics department of the GeoGrid Center have hands-on experience in using data from in-depth electric prospecting (MT sounding, near-field transient electromagnetic sounding, telluric current methods), magnetic prospecting and gravity prospecting to solve geophysical problems, including petroleum fields exploration, via the comprehensive approach.