| The Time Factor |
| Features | |
| Written by Matt Bolch | |
 We report on several oil and gas companies finding 4D seismic imaging a useful tool to maximize production. Although 4D seismic imaging has been around for more than a decade, the time-lapse imaging still faces a few issues, including cost, said Jaime Stein, chief geoscientist at Geotrace, the Houston-based provider of such services as data management, reservoir characterization and modeling, and sensor technology. 4D imaging goes beyond the traditional 3D model by adding the element of time. As a deposit of oil or gas is transferred to the surface, movement within the deposit can leave pockets of product that the well cannot pick up. Because 4D uses stationary hydrophones (for ocean wells) or geophones (for land wells), a periodic snapshot of the deposit can be taken to figure out where the pockets are, allowing the drilling of supplementary wells or predicting how much product is left to be extracted. “It’s a great tool to determine whether anything has been left in the ground,” explained Stein. “There may be sealed pockets not connected to the main deposit.” One concern with 4D seismic imaging involves the repeatability of surveys to ensure that data from subsequent measurements accurately reflect any changes. Stein likens 4D imaging to comparing a photo of someone taken a year ago and today. Variations in the image can occur because of differences in the camera used, the lighting, changes in the person’s weight and health, and other factors. “There can be false positives, so you have to make sure the difference is hydrocarbon-related and not the difference between summer and winter readings, different equipment, or other factors,” Stein said. “You need to be able to say with some certainty how the field has evolved.” Leveling the playing field The decline in oil prices may benefit the evolving 4D technology. When oil is $140 a barrel, the lion’s share of resources are spent helping customers find oil. When production drops, engineers have more time to devote to R&D, which means the development of more accurate technology by the next time boom times arrive. Past R&D developments have brought the price of 4D seismic imaging down to a point where small independents can afford to use the technology, leveling the playing field among exploration companies. “I wish it was used all the time,” Stein said of 4D technology. “In the past, it was reserved for very large fields and companies with deep pockets. But now that the equipment is better and less expensive, companies of any size can use 4D.” Houston-based Hyperdynamics Corp. believes it will be using 4D imaging as it begins to drill production wells in the 31,000 square miles it has leased offshore of the Republic of Guinea in West Africa. The oil and gas exploration company also has oil production rights in Louisiana. After acquiring the leases, Hyperdynamics first conducted 2D imaging to develop a regional picture of likely deposits. The company now is embarking on the first 3D imaging in the shores off Guinea to specifically identify where it wants to drill first. Once successful test wells are drilled, the company likely will use 4D seismic imaging to maximize production, said Jim Spear, vice president of exploration and production at Hyperdynamics. “After drilling delineation wells to define the depth of the field so we can build the necessary infrastructure, we want to determine how that field is producing, and that’s where 4D comes into the picture,” said Spear. The main use of 4D is to maximize production. Spear said 3D imaging can cost between $20 million and $40 million, depending on the size of the area to be surveyed. Production wells can cost upward of $30 million to drill, not counting the cost of the related infrastructure, which can add another $750,000 a day. 4D imaging can help companies monitor the field, identify nearby pockets not connected to the main field, and help solve dollars-and-cents equations related to return versus cost. “4D gives you a better decline curve,” Spear said. “In the last 10 years, it’s becoming more widely used due to reservoir maintenance. A good reservoir manager wants to maximize production in a given field. As fluids migrate, 4D helps enhance the ability to produce and maintain a field.” Once a production field is identified, hydrophones are anchored on the bottom of the ocean floor. At set intervals, often every six months to two years, seismic data is collected and evaluated to monitor depletion of the field and map the migration of hydrocarbons over time. “Rigs are costly, and drilling is costly,” Spear said. “4D is expensive, too, but once the monitoring devices are laid down, you get a lot of return,” Spear said. Extra oil StatoilHydro estimates that 4D seismic imaging has helped improve production in its Gullfaks field in the North Sea by more than 60 million barrels of extra oil, said Reidar Helland, head of petroleum technology, during remarks at the World Petroleum Congress. The expected recovery factor in the field now tops 60%. StatoilHydro first used 4D seismic technology in 1996 and has drilled 17 wells at Gullfaks based on 4D seismic data. Helland said he doubted those wells would have been drilled without 4D data. The company hopes to achieve a recovery factor in the Gullfaks field of 70% and extend the life of the field to 2030. Stein from Geotrace notes that 4D imaging was developed for land use but now is employed primarily in marine environments, including in the North Sea and the waters surrounding the oil-rich Middle East. “Every year, we as an industry are getting better at equalizing 4D data so we can paint an accurate picture,” he said. Matt Bolch, This e-mail address is being protected from spam bots, you need JavaScript enabled to view it , is a freelance writer based in Atlanta. |
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