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Mexico’s Deepwater Geology

Tue, 01/22/2013 - 17:29

During the first few years of Pemex’s venture into deepwater, the E&P division devoted itself to learning new geologic acquisition technologies and applying them across the 500,000km2 of the Perdido folded belt. “In 2007 we defined a new strategy for geological surveys, establishing that the first step would be to identify the areas with the highest probability of containing liquid hydrocarbons. This initial phase was carried out through regional geological and geochemical modeling,” recalls José Antonio Escalera Alcocer, Subdirector of Exploration at Pemex E&P.

Five different elements need to be understood in any exploration project: the source rock, the reservoir rock, the trap, the seal, and the sync and migration. “The first step in the modeling phase of an exploration project is to identify where the source rock is located. In order to do this, you have to determine where the proper conditions are available for the rock to be in the source window, whether the search is for oil or gas resources,” Escalera Alcocer explains. “The key is to find those five elements within the surveyed geology and work methodically through the exploration process, without skipping any stage, since that would lower our probability of success. This has required a long understanding and training process, and has further allowed us success rates above normal industry levels.”

For Pemex to follow the procedure that Escalera Alcocer describes, the E&P division hired a vessel to acquire 3D seismic data for five years, at the same time that they contracted the necessary rigs and platforms, anticipating the market dynamics. “The deepwater area we surveyed consisted of 120,000km2. Due to the large area we were trying to cover, we had to perform 2D or 3D seismic studies,” Escalera Alcocer says. “The acquisition of seismic data that the 8km extension of the 12 cables on the vessel produced was a key component in enabling us to see the subsea structures.”

Application of both 2D and 3D seismic allowed Pemex to elaborate geological and geochemical models and focus on inversions. The exploration division devoted itself to understanding and interpreting the results of those surveys to create a list of priorities in deepwater, but they found some challenging aspects within the geology of the region. The effect of salt layers in the Perdido folded belt, such as the saline province of Bravo, stopped the creation of accurate subsea structure models with that technology. This made Pemex take a step forward and use wide azimuth technologies to better understand the formations that data interpreters initially could not see. “We performed a wide azimuth survey across almost 24,000km2,” Escalera Alcocer adds. “Without this technology, we would not have been able to see our work area, and that would have prohibited us from operating effectively. Seismic was extremely beneficial and allowed us to visualize all the elements in the oil system, reduce cycle times and identify Trion.”

“The key to understanding the operation was going back to regional models, mastering the geological and geochemical modeling processes, regional sedimentary models and predictive models,” Escalera Alcocer stresses. “Even though the technology involved in seismic acquisition plays an essential role in modeling subsea geology, it is extremely important to understand the regional context, since that is the fundamental factor that defines where seismic investments should be made.”