Mention asset integrity in the oil and gas sector today, and many undoubtedly will look to the physical assets that represent the oil and gas project life cycle, from the assignment of drilling rigs and identifying exploratory wells through to the front-end engineering and design and construction phases as production operations get under way.
In reality, however, asset integrity and asset management start much earlier in the process, as operators seek to make sense of the geological data coming from the single biggest asset – the targeted reservoir. One challenge in the management of operators’ reservoir assets is maximizing the value of these geological data.
While seismic interpretation technologies have improved dramatically over the last few years in developing geologically consistent 3-D representations of the subsurface, too often operators remain dependent on highly generalized geological models. No one disputes the gigabytes of data that are being generated, yet much of these data end up being condensed into a few kilobytes of valuable interpreted data. The result is that potentially valuable seismic information is lost.
So how can seismic interpretation technologies improve their performance and play a crucial role in asset integrity management (AIM)? How can greater detail of structural geologies be generated to maximize assets?
Meeting the challenges of geological complexity
As operators look to more remote regions when expanding their reservoir assets, it is clear that the resulting geological complexities have increased.
Whether it is limited seismic coverage; the decline in classical structural traps; presalt and post-salt areas; or unconventional resources such as tight gas, oil shales, and oil sands; the pressure is on seismic interpretation technologies to extract maximum value from multiple volumes of often complex seismic and geological data. The signs are, however, that seismic interpretation is meeting these challenges.
Take the need to detect more subtle traps and reservoir fluid content in seismic interpretation. To meet this need, it is important to provide the interpreter with a better understanding of both seismic stratigraphy and fluid migration.
dGB’s seismic interpretation software, for example, now can reconstruct the history of deposition in geological time as well as cross-correlate events between wells through the tracking of chronostratigraphic horizons. This results in a more accurate targeting of reservoir, source rock, and seal potential.
In terms of fluid migration, the growing emergence of chimney cubes – the vertical noise trails that are generated when hydrocarbons migrate upwards – also has enabled the interpreter to follow the fluid migration paths from deep thermally mature source rocks into the trap and upward to the surface, thus generating vital information about the petroleum system.
Chimney probability cubes also can be generated to obtain a qualitative measurement of fault leakage.
Furthermore, through the study of spatial relationships among faults, chimneys, and trap configurations, chimney cubes can be used for prospect ranking.
Attribute analysis also is playing a key role in revealing otherwise hidden geological information. This is being achieved through the increasing sophistication of multivolume, interactive attribute analysis where users can target and calculate attributes, test attribute parameters, create their own attributes to find the optimal setting for their data, and access filtering and processing capabilities.
Increasing the number of horizons
Another means of improving the detail of structural geologies as a means of maximizing reservoir assets is through increasing both the number and density of tracked horizons in the seismic interpretation process. This can increase the potential of high-resolution seismic in reservoir characterization and lead to an improvement in low-frequency model building.
In a new module for seismic interpretation, a dense set of correlated 3-D stratigraphic surfaces are, through an advanced algorithm, developed into a set of continuous, chronologically consistent horizons.
These auto-tracked horizons allow a detailed and accurate low-frequency model to be developed with the differences shown in regard to not only the quality of the model, but also the quality of the acoustic impedance inversions.
It also opens up a host of new editing possibilities. Tracked events, for example, can be assigned a relative geological age with a corresponding color using an interactive slider to add or remove chronostratigraphic events.
And the benefits for seismic interpreters include improved quantitative rock property estimation, enhanced definitions of stratigraphic traps, more accurate and robust geological models, and the ability for interpreters to extract more from their high-resolution seismic data.
The importance of peer review
For all the developments and expertise being put into seismic interpretation technologies today, the best means of ensuring that such software packages meet today’s asset integrity needs is through continuous peer review.
dGB’s seismic interpretation software is available on an open-source seismic interpretation platform that has been downloaded more than 30,000 times since Sept. 1, 2009, with many users providing important feedback. Several oil and gas companies as well as service companies have used the software, and to date about 200 universities have incorporated it into their teaching and research, with more than 1,000 free commercial licenses adopted in universities in Europe, the Middle East, Africa, Asia and Asia Pacific, and the Americas. The latest academic partnership in July 2010 saw the donation of US $4.8 million of commercial licenses to 20 universities across Nigeria.
dGB also recently provided software to the University of Pittsburgh, which, according to the visiting professor at the university, will help drilling companies currently exploring and extracting natural gas from the Marcellus shale layer of Pennsylvania.
Along with being able to use the software, the universities also can access an extensive database of seismic data, interpreted horizons, and well data from a number of global locations, including Central Alaska, offshore Netherlands, and the North Atlantic Ocean offshore Canada.
Skills transfer, workflow integration
An open-source base system, unprotected by licensing software, also supports two other important developments in seismic interpretation – the fast-track development of easy-to-use interpretation tools and the integration with existing workflows.
With the shortage of graduates entering the oil and gas industry and a workforce reaching retirement age, it is vital for future asset integrity that skills can be transferred easily. That is why many seismic integration packages currently come with a host of new visualization and editing features.
The same goes for integration. Seismic interpretation now has application across the entire reservoir management workflow. An accurate workflow and integration with other data sources ensures that best practices are disseminated, guidelines are established for those entering the sector, and a sound basis for uncertainty assessments and AIM decisions is provided.
With this in mind, it has been particularly important that seismic interpretation has an integrated workflow that covers not only geology and geophysics applications but that can be fed into future reservoir models and reservoir management decision-making.
While no one can claim that there will not always be a large element of uncertainty in reservoir management decisions, there is still much that can be done to ensure decisions are made with the maximum amount of information and that assets are fully optimized. Seismic interpretation is a key tool in achieving this.
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