Enhancing Production Recovery in Brownfields Using 4D Seismic Survey

Enhancing Production Recovery in Brownfields Using 4D Seismic Survey

Conventional brownfields account for roughly 65% of global crude oil production, a percentage that is even higher in Egypt at 77%. The majority of these old fields are in the Gulf of Suez and the Western Desert, from which more than half of Egypt crude oil production comes.

Until now, new discoveries are not matching the declining production in Egypt’s mature oil fields. Egyptian production of crude oil peaked in 1993 when it exceeded the level of 910,000 barrels per day (b/d); however, it has been declining since then, and it is expected to further decline and bottom out by 2029, according to Wood Mackenzie’s “Egypt Upstream Summary” report.

Meanwhile, exploration and production (E&P) witnessed a number of technological breakthroughs in recent decades, one of which is the four-dimensional (4D) seismic survey. 4D seismic survey is an advanced well-established data acquisition technique, which uses multiple seismic surveys of a producing field during a certain period in order to determine changes in reservoirs over time.

“In general, 4D seismic aims at visualizing the movement of fluids within the reservoir and help design the optimal production strategy with the final objective of maximizing the recovery of hydrocarbons from the subsurface. Although reservoir engineers have a very clear picture of the status at the well locations, they can only assume, or infer what happens in between wells,” Panos Doulgeris, Co-founder of Delft Inversion, told Egypt Oil & Gas.

“4D seismic data have the potential to provide information on production effects away from the wells,” he added. “I am always amazed by the accuracy achieved in predicting time-lapse effects within a reservoir that may lie more than 4,000 meters below our feet, just by measuring information at the surface.”

Schlumberger defines the technique as 3D seismic data acquired at different times over the same area, in order to assess changes in a producing hydrocarbon reservoir over time. Changes may be observed in fluid location and saturation, pressure and temperature. It is one of the several forms of time-lapse seismic data that can be acquired on the surface or in a borehole. It is worth noting that it can also be conducted via repeated 2D surveys.

“A more precise term is repeated seismic… a seismic survey over a given area [such as an oil or natural gas field] is repeated in order to monitor production changes. Time-lapse seismic is another term used for this,” according to Knut Bjørlykke and Martin Landro’s paper published in Petroleum Geoscience.

4D or time-lapse seismic survey is applied in monitoring three major things, namely the changes in a producing hydrocarbon reservoir, underground storage of carbon dioxide (CO2), and geohazards, such as landslides and volcanoes, according to Bjørlykke and Landro.

Time-lapse seismic survey could play an essential role in brownfield development, especially in terms of decision making and determining the best ways that could be used to capitalize on reserves in mature hydrocarbon fields, as it assists in reservoir characterization, identifying the movement of fluid interfaces and locating reserves. It has also become a worldwide-recognized technique, as it provides higher accuracy and a clearer understanding of reservoirs, as well as guiding the selection of the best possible technique that could be applied in production, as different circumstances require different techniques.

4D Seismic Survey in Egypt    

“The deployment of time-lapse seismic as a tool to enhance the production of hydrocarbons hinges on both the commercial and the technical feasibility of the method in Egypt. On the commercial side, the profit margins of natural gas-producing assets are typically not high enough, especially offshore, to justify the cost of acquiring a time-lapse seismic survey,” Doulgeris explained.

When it comes to natural gas, in specific, given Egypt’s strong position in proven natural gas reserves and its rising daily production, exceeding 6.5 billion cubic feet per day (bcf/d), the limited use of time-lapse seismic in gas fields can be explained. However, with the move towards ultra-deepwater in Eastern Mediterranean, a paradigm shift towards the use of more 4D seismic can occur, as the information derived from such processes can prove very valuable when drilling very expensive ultra-deep-water wells, he further noted.

“From a technical point of view, the monitoring of fluid changes in the reservoir is generally more challenging in carbonate than in sandstone reservoirs. This limits the applicability of the method in Egypt, as many of the reservoirs are carbonates. We also need to keep in mind that 4D seismic requests high-fidelity repetition of all the conditions regarding the acquisition and processing of the data in order to explore the very subtle differences between two datasets that have been acquired at a different point in time,” Doulgeris indicated.

“Land data, especially from the Western Desert, often exhibit a low quality that may act as an impediment for the further deployment of 4D seismic surveys. However, technological advances in the processing of time-lapse data, such as joint seismic inversion, can increase the value of information extracted and help in this way build the required business cases around the use of 4D seismic in Egypt,” he added.

Speaking of how Egypt can boost the use of modern technologies in the petroleum sector, the Co-founder of Delft Inversion stressed his belief that innovation in the sector is not only driven by major service and operating companies but also smaller technology companies.

“A major hurdle these companies could face to extend their services to Egypt is the long registration and verification time required to start doing business. The simplification of the process along with fiscal motives for operators to test new methodologies would certainly grow the influx of new modern technologies into the country,” he noted.

Business Aspects

The acquisition, processing, and interpretation of data collected in 4D seismic surveys have budgetary consequences. Increasing the recovery factor of a reservoir, even by a small rate, significantly impacts revenues, which is a determining factor in brownfield development, according to CGGVeritas, a Paris-based geoscience company that has been using 4D seismic for more than 20 years now.

“With maturing basins and even deeper and more complex frontiers, the importance of extending the life of and maximizing recovery from producing fields has never been greater,” the French company explained.

The technique clearly provides economic and business advantages, as it facilitates the detection and extraction of oil trapped below complex surfaces. “Since 4D seismic can be used to identify [oil] pockets, it is easy to understand the commercial value of such a tool. However, if the reservoir geometry is simpler, the number of untapped hydrocarbon pockets will be less and the business benefit correspondingly lower,” Bjørlykke and Landro wrote.

Although the accuracy of the technique was originally limited to being a qualitative indicator of production effects, advances in technology, especially 4D processing, have allowed the production of more precise 4D seismic data that is transformed into the context of reservoir engineering.

The technique also witnessed a shift from being a purely geophysical interpretation tool to a reservoir management tool, which can be used to assess the remaining hydrocarbon volumes and optimize the recovery strategy through quantitative estimates of changes in reservoir properties such as fluid saturation and pressure, according to CGGVeritas.

As Egypt aims at meeting the rising local demand and ensuring energy security, 4D seismic survey could be a key technology to help in capitalizing on mature oil and natural gas fields, thus increasing brownfield production alongside that of new discoveries, while introducing state-of-the-art technologies, modernizing production recovery practices, as well as training the needed technical expertise to apply modern techniques.


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