The geosciences continue to expand into the life-of-field arena by integrating an array of technologies. With the American Association of Petroleum Geologists (AAPG) and the European Association of Geoscientists & Engineers (EAGE) holding conferences at the same time in June, several suppliers took advantage of the timing to introduce new and improved products. Following are some of those:
At the EAGE conference and exhibition and also AAPG, Paradigm debuted its Rock & Fluid Canvas 2009 | Epos. The system uses a higher-order workflow designed to use a variety of applications on the common platform provided by the Epos infrastructure. It combines geopohysics, geology, petrophysics, and drilling engineering suites.
“This allows the user to explore the design and to interact with the subsurface data at any point using all available data…well logs, seismic, petrophysics, even to geosteering,” says Duane Dopkin, Paradigm senior vice president, technology. “Users can integrate data from Earth Decision acquisition to subsurface modeling via SKUA. And Epos enables scalability for multiple users on the same project.”
Paradigm’s Rock & Fluid Canvas is based on pulling data from where ever they are and adding them to an extendible “canvas.”
Once the data is collected, Dopkin says the prospect is scalable up to regional scale and also from a regional scale down to the prospect. It can be used for scenario modeling with repeat workflows to capture uncertainties in the scenarios.
Desktop 3D seismic
Also at EAGE, ffA released SEA 3D Pro 2009, the next version of its desktop 3D seismic analysis and volume interpretation software running on Linux. According to ffA, this new version extends its range of interactive analysis including a seismic facies classification module, additions to its frequency decomposition, multi-attribute color and opacity blending, and iso-proportional slicing.
The new program has an interactive link with GeoProbe 3D software from Landmark for volume interpretation.
New 4D inversion algorithm
A new global 4D inversion algorithm is available for application to time-lapse reservoir characterization using more than two vintage seismic data sets.
This provides a framework to monitor production-induced fluid movements with 4D seismic. The use of smart 4D constraints reduces the inherent non-uniqueness of 4D inversion and produces more accurate quantitative results consistent with the expected production effects, says developer Hampson-Russell Software & Services.
This approach was used for the time-lapse monitoring of reservoir fluids in the Brage field in the Norwegian North Sea. It has been in production since 1993. The study aimed to identify undrained oil sands in order to extend the life of the field.
The 4D processing of the 1992 base and 2003 monitor surveys was performed by CGGVeritas. It included anisotropic (TTI) pre-stack depth migration to accurately position the reservoir’s bounding faults and optimum focusing of events in the migrated gathers. A “4D mask” was defined using an energy attribute cube, computed from 2003-1992 amplitude differences. For cells outside the mask (i.e. with minimal 4D difference) a time-invariant solution was sought so that the model had the same values at base and monitor survey times. Inside the 4D mask, the allowed ranges of Vp, Vs, and ρ variations between base and monitor surveys were determined from fluid substitution analysis: water injection is expected to increase Vp and ρ by a maximum of 5% and decrease Vs by up to 2%. Pressure effects on the 4D response were expected to be small and therefore were excluded in the definition of the 4D constraints. The results of the 4D global inversion and 4D Bayesian fluid classification are shown in as maps of oil-sand probability which depict changes in fluid distribution after 10 years of production. They are broadly consistent with expected effects of the water flooding and also are supported by water saturation logged along the path of a horizontal well drilled in 2005, Hampson-Russell says.
Analysis development
In the global 4D inversion, joint perturbations of Vp, Vs, and ρ values are introduced for the base and all monitor surveys, and are accepted or rejected as a whole to find the best fit for all the vintages. To incorporate 4D constraints, the inversion uses a simulated annealing procedure adapted to the multi-vintage setting. According to Hampson-Russell, this allows user control over the level of 4D coupling which can be expressed in terms of simple rock physics rules restricting the range of variations between consecutive surveys.
For example, if water injection takes place between the base and monitor survey times, a large increase in Vp but only a small decrease in Vs due to the density change is expected. Appropriate limits on the variation of these parameters can be set. Outside the reservoir further constraints can be applied. In areas where no 4D effect is expected or observed, a model optimization is performed across all vintages to reduce the impact of non-repeatable noise on the inversion results.
The 4D coupling introduced in the global inversion identifies solutions consistent with observed production data and a priori knowledge of the reservoir. This is vital in reducing the non-uniqueness of 4D inversion and it results in more accurate, quantitative estimates of changes in reservoir properties, says Hampson-Russell.
The interpretation of elastic attributes from inversion can be aided by lithology or fluid classification. The principle is to determine the ranges of elastic attributes corresponding to particular lithology and fluid combinations. Hampson-Russell uses a Bayesian classification scheme involving multivariate probability distribution functions. This recognizes that elastic attributes from different lithologies can overlap and the inversion results should, therefore, be described in terms of percentage probability of belonging to one or more of the defined litho-classes.
Cascading global 4D inversion with 4D Bayesian lithology classification allows reservoir properties, in particular fluid saturation, to be derived from the elastic attributes. It facilitates interpretation by clearly showing the evolution in the fluid distribution over time and quantifying the uncertainty in the inversion results.
Geoscience Workbench
Fugro-Jason announced availability of another version of its Jason Geoscience Workbench with new AVO attribute/analysis and full waveform synthetics applications, and a series of enhancements to existing products. JGW integrates geological, geophysical, petrophysical, and rock physics information into a single consistent model of the earth.
“This latest release, driven by user requests, expands JGW to encompass additional seismic interpretation and analysis tools,” says Joe Jacquot, marketing manager for Fugro-Jason. “With these new tools and enhancements, our customers will be able to do a better job of integrating traditional seismic AVO analysis and JGW seismic inversion.” The AVO attribute/analysis module will allow extraction of seismic AVA or AVO attributes from pre- or partial stack seismic data. Options include:
- Shuey 2-term (intercept and gradient)
- Shuey 3-term (intercept, gradient, and far-offset)
- Smith and Gidlow (Vp and Vs contrasts)
- Fatti et al. (Zp and Zs contrasts)
- Gray et al. (λ, μ and ρ contrasts).
This add-on application to the Well Log Editor provides full waveform synthetics. Pre- and post-stack NMO synthetics with and without multiples can now be calculated. Using well control, this module allows analysis of which seismic events are primaries and which ones are not.
The new release also includes enhancements to existing applications including a new spectral decomposition module, improvements to the deterministic inversion and wavelet estimation algorithms, and usability enhancements.
Release is scheduled for the third quarter of this year.
Processing toolkit extension
Just prior to the opening of the conferences, GX Technology (GXT) announced an extension to its toolkit for processing seismic data acquired in difficult subsurface environments including subsalt. Two enhancements to GXT’s technology toolkit are the ability to handle marine seismic data acquired using complex-azimuth (CAZ) geometries, including wide-azimuth and rich-azimuth datasets, and the ability to incorporate anisotropy in full commercial production across all elements of the seismic workflow, including velocity model building using tomography and reverse time migration (RTM).
Nick Bernitsas, senior vice president of ION’s GXT Imaging Solutions group, says, “Wide-azimuth surveys are becoming increasingly commonplace in challenging imaging environments like the Gulf of Mexico. These datasets take the degree of processing complexity to new levels. With the enhancements we have made to our imaging toolkit, we can now deliver a more accurate representation of the sub-surface to our clients in a timely and efficient manner.”
