New technology integrates prestack seismic insight into mainstream interpretation workflows
Kenny Laughlin, Janet Hicks - Landmark
Prestack seismic data can provide unmatched insight into a reservoir’s potential. In today’s landscape of high-risk and complex assets, such insight can be key to avoid nonproductive time and to successfully overcome geoscience challenges like fluid and lithology delineation, tight gas detection, deepwater exploration, and fractured reservoirs.
Despite the advantages of integrating prestack data into seismic interpretation workflows, significant barriers to incorporating the format, such as the limited storage capacity and interpretation abilities of available technologies remain. These limitations prevent most interpreters from leveraging prestack data in their subsurface analyses. The format has been relegated instead to use by amplitude offset specialists and seismic processors. With these experts in short supply, the industry continues to embrace the easier-to-use poststack format.
Prospect panel comparisons at wet versus pay versus prospect locations leveraging prestack data.
Now, leading upstream technology providers, including Landmark, are leveraging advancements in computing power, storage capabilities, and analysis tools to harness prestack seismic data and integrate it into standardized interpretation workflows – bringing this important data type directly to interpreters’ desktops. This convenient, efficient access to prestack data allows interpreters to accurately identify fluid and lithology changes, bypassed pay zones and new reserves, and to more confidently pursue plays that were previously thought to be too risky for development.
There are many reasons exploration and production operators jumped at the chance to use poststack data when it was invented more than 40 years ago. Namely, it made seismic interpretation manageable for the first time.
Prestack data traditionally is in a cumbersome format impossible to integrate into standardized workflows. The sheer size of the data, 50 to 100 times larger than poststack volumes, means generally it has been stored only on its original tapes. Interpreters ambitious enough to seek out prestack seismic data were forced into a tedious process to coordinate data management personnel to identify and recover the tapes containing the desired data, to locate the appropriate tape drive to view the data, or remastering the tape onto new media, and then to load the format and running a quality control check. The entire process could take weeks.
However, interpreters turning to more convenient, condensed poststack data sacrifice a level of accuracy in their subsurface imaging and analysis that can result in lower-than-expected well performance or even dry holes. Integrating prestack data into interpretation workflows can lead to more confident prospect identification and field development by allowing interpreters to quickly verify their poststack data analysis, rapidly reprocess data when questions of seismic data integrity arise, and better predict subsurface fluid and lithology effects.
The value of prestack data
Most processors working with seismic data are challenged to create the best possible image of a specific target. As a result, the images of the surrounding subsurface often are unclear. However, as the target is examined and compared to other wells, new opportunities often appear that also need evaluation. The technologies behind the latest prestack seismic interpretation workflows provide for the integration of prestack data in project management systems such as Landmark’s OpenWorks database, rather than at the application level, making it a native, managed data type in the interpreter’s software. This allows an interpreter to quickly reinterpret the prestack seismic data for that area and to evaluate these additional opportunities in real time.
Gathers above stack with AVO header plot.
Further, when questions of data integrity arise, convenient online access to prestack data from applications like the OpenWorks software allows interpreters to reprocess data immediately without having to completely revise the drilling and evaluation schedule. This is important if questions about the initial interpretation arise late in the field development cycle – at a time when rigs already are contracted and the costs of delays are high.
Particularly relevant to challenging deepwater operations is the ability to use new, mainstream interpretation technology to predict changes in reservoir fluids and lithology directly from the prestack data. Combined with velocity analysis, the prestack data is essential to determine the difference between fluids such as gas, oil or brine, and lithologies such as sand, lime, shale, igneous or salt, as well as to predict pore pressure. This information leads to more accurate interpretation and more informed decision-making in multi-million dollar deepwater drilling programs.
The use of prestack data in other unconventional plays is less established, but is increasing as economics change and as operators look to produce areas where traditional poststack data has failed. For example, interpreters can leverage the subtleties in prestack data to determine fracture orientation in carbonates and tight sands.
The end result for an operator using prestack seismic data is greater confidence that production targets can be met and development plans will succeed. This is critical information at a time when extracting additional pay from existing fields and identifying new reserve zones in unconventional fields is imperative to every oil and gas company’s continued sustainability.
Recognizing prestack potential
One national oil company recently was able to generate substantial savings in its exploratory well operations, and to reduce significantly its data processing costs by giving its geophysicists convenient, online access to prestack data.
The company, seeking to enhance its hydrocarbon detection efforts, implemented Landmark’s prestack data on the desktop workflow and a rigorous prestack data management system, ensuring that interpreters had quick, easy access to the right data.
Gather comparison at two different well locations with stack, VSP, and prestack seismic data with log curves.
Using the prestack interpretation software as an integration platform, the company’s interpreters were able to view not only prestack data, but also high-quality well logs, poststack seismic data, horizons, and faults – at the same time. As a result, the company was able to significantly lower its subsurface risks by correlating well information to both prestack and poststack seismic data.
Access to the prestack data was simply through a highly efficient and flexible data management system based on Landmark’s comprehensive PetroBank database. Traditionally, the company’s prestack seismic data had been nearly inaccessible. The company stored terabytes of data on hundreds of thousands of magnetic tapes in a large storage facility. To rectify the situation, the company created a system to access prestack files on high-speed, high-capacity disks. This allows interpreters to identify directly the seismic survey and data they seek, then outline the desired data in a map view, submit an online request, then download the data.
Making prestack seismic data use more routine not only has saved the company money, but also has allowed rapid re-affirmation of an important drilling location. Indications at the proposed location showed overpressure, necessitating a re-examination of the seismic data for the area. Previously, this would have taken nearly a week, causing the company to abandon the location. However, with the new data management system and prestack data interpretation applications, the company was able to generate new data in a day and half, and drilling proceeded as planned.
While the benefits of integrating prestack seismic data into interpretation workflows are clear, the traditionally cumbersome nature of the prestack data format has led most oil and gas operators to turn almost exclusively to poststack data. Now, cutting-edge technologies are available to make prestack seismic data available in standardized interpretation workflows.
The convenient access provided by these new tools allows operators to leverage prestack data’s unique reservoir insight to effectively execute strategic prospecting and development operations, even in the most complex fields.
