/
Analysis

Electromagnetic Data Acquisition in Mexico

Wed, 01/22/2014 - 10:16

A leader in the electromagnetic (EM) data acquisition market, EMGS is working in the deepwater areas of the Gulf of Mexico. Its activities on the US side involve carrying out a multi-client survey in Alaminos Canyon, a prominent oil region for large IOCs. This is a direct offshoot of work EMGS has previously done in the deepwater Perdido Fold Belt region in northern Mexico. The company uses its specializations in Controlled-Source Electromagnetic Surveys (CSEM) and Magnetotelluric Surveys (MT) to provide better structural modeling. By integrating these methods with traditional exploration techniques, such as resistivity and seismic data, it is able to produce smooth subsurface images for its clients. The application of these technologies enables EMGS’ clients to reduce geological risk by increasing the visibility of the desired geological target, leading to improved chances of exploration success. EMGS uses vessels with submersible receivers to reach the significant depths required for the imaging of offshore reservoirs. These receivers are released from the vessel to be laid out on the surface of the seafloor and where they are held by dissolvable concrete slabs. “We are putting down 150 receivers in a given layout, which are spread a couple kilometers apart and thus cover a very wide area,” states David Hicks, President Western Hemisphere and Multiclient of EMGS. CSEM and MT data acquisition techniques have different yet interrelated purposes, explains Hicks, adding that they both involve the mapping of the stratigraphic horizons of potential reservoirs. In CSEM surveying, a horizontal electric dipole is introduced about 30m above the seafloor, which transmits a lowfrequency electromagnetic signal into the subsurface to map resistive bodies. Differences in pore fluid resistivity provide the results that characterize geologic structures, which can then be analyzed for their hydrocarbon potential. By combining CSEM with seismic data, a highresolution image is produced that clients can use to assess drilling feasibility at a certain location. While MT also works with the response of resistive formations, it measures the electric and magnetic fields on the seabed when the controlled-source is inactive during a CSEM survey. Utilizing these fields enables deep penetration, which shows up a view of thicker layers while also interpreting regional geology. Moreover, MT surveys are very useful to define a salt structure’s base and boundaries, making it an interesting option for offshore operators in the Gulf of Mexico. Considering that CSEM focuses on more subtle hydrocarbon indicators in the subsurface, MT complements EMGS’ data acquisition techniques to provide an overview of the prospect at hand.

Besides providing results when delimiting hydrocarbonbearing reservoirs and salt geometries, EMGS is proficient at establishing volumetric assessments for the exploration workflow. After all the data is obtained, processing, postmodeling, and inversion are performed to produce 3D resistivity volumes, which allow companies to better determine the plausibility of their projects through Quantitative Interpretation (QI). This method essentially analyzes a reservoir’s volume, which Hicks refers to as “barrels of resistivity”. “There is a vertical variation in the resolution of the data but typically we get excellent horizontal resolution. Then, if a company believes that a body contains hydrocarbons, we can go in quantitatively and carry out a variety of measurements, such as water saturation, and provide a good picture of what the ultimate reserves are. This process can lead to 4D work, where one can go back and look at how the reservoir changes over time.”

Hicks explains that his firm has come to understand the geology of the Gulf of Mexico very well. “When you look north of the border, the Gulf of Mexico on the US side is like a global laboratory for intensive imaging and exploration, which is right across the border from Mexico’s somewhat virgin territory. I think there is going to be a tremendous boom,” Hicks affirms. The company is currently based in Villahermosa, where it works with senior geoscientists that have experience in offshore exploration in the Gulf of Mexico. He sees it as an objective to extend the exploratory successes that have been enjoyed on the US side of the Gulf of Mexico oil regions to Mexican reservoirs. “If we could map the entire Wilcox trend across the border through the Perdido region with CSEM and seismic data, it would be a tremendous exploration product.”

Having worked with PEMEX’s deepwater prospects such as Supremus and Maximino during the past three years, the firm has established a presence in the country’s exploration market. Moreover, EMGS is proud of its track record by not ever having given a misdiagnosis when executing surveys and data processing for PEMEX to analyze a potential hydrocarbon opportunity. Hicks delves deeper into the surveying process, explaining that each one first involves the definition of a prospective area by PEMEX’s asset team and EMGS staff. After that, selecting the appropriate method for this project becomes a more tailored process. “Instead of simply going out and shooting seismic through whichever method and area, we go in ahead of time and do a sensitivity analysis to decide the right area for our end technology,” he describes. This precision makes well placement an easier task for PEMEX or any other operator.

In terms of cost-maximizing opportunities, Hicks highlights the importance of a sound exploration workflow, which can be obtained through the integration of an EM survey with seismic and well data. “If integrated correctly, a company truly increases its success percentage, with a combination that really boosts the prospect’s potential. If a firm is going to spend US$200 million or more to drill a deepwater well, it makes complete sense to spend US$10 million to integrate all of its data to increase its chances of success. Economically, it makes a lot of sense,” he asserts. Additionally, and relevantly to PEMEX and other future operators to the Gulf of Mexico, Hicks thinks that this combination of techniques could prove to be an effective imaging method for sub-salt structures in shallow waters and deepwater. EMGS has already had experience with similar cases in the US and is planning how to apply this knowledge to Mexico’s specific geological challenges.