CSEM-Driven Exploration in the Gulf of Mexico

Stefatos, Aristofanis ¹; Monsen, Rolf ¹; Vereshagin, Alexander ¹; Alaeimajolan, Behzad ¹; Hesthammer, Jonny ¹
(1)Rocksource ASA, Bergen, Norway.

The extensive distribution of salt bodies in combination with relatively small size and low resistivity pays in the Gulf of Mexico (GOM) have inhibited most E&P companies from incorporating the Controlled Source ElectroMagnetic (CSEM) technology in their exploration tools in this region. In 2009, Rocksource decided to start exploring for hydrocarbons in the GOM using the CSEM technology as the primary driver. This decision was founded on confidence built on previously gained experience from the application of the technology in many basins worldwide and the positive evaluation of already acquired CSEM surveys over a number of prospects in the GOM. Today the company has built a portfolio of 17 leases and has increased the available CSEM data through acquisition of new surveys to a total of 13 surveys.

Besides the known challenges posed by salt and weak pay resistivity contrast to the surroundings, the GOM was proven a challenging operational environment. Steep sloping seafloor and extensive infrastructure on the seabed require very careful survey designs and experienced offshore crew to run the operations. The bathymetry variations can be dealt with during the data processing. However, the infrastructure poses restrictions on equipment deployment and navigation and has the potential to corrupt the data by increasing the noise and inducing artifacts. Operating in the GOM offers the advantage of having dense well coverage.

Well log data provide important control points for the inverted CSEM resistivity maps of the subsurface. Being aware of the difficulties and through careful planning and modeling it was possible to acquire good quality data that contributed significant value in the exploration of the GOM.

The CSEM data allowed the identification and de-risking of the prospects that appear to be resistive. The value of the information was highlighted in surveys where the derived subsurface resistivity was matching the existing well log data. In addition some of the data resolved unexpected resistivity anomalies in areas that were later associated to new prospects. At least three new prospects were generated on the basis of the CSEM resistivity information that focused the attention on a previously overlooked prospect, a prospect within a new play concept, and finally on a prospect without clear seismic amplitude signature.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.