Innovators in Geosciences Series

Eastern Mexico's New Potential, Both Onshore and Offshore: Interview with Stephen Cossey

American Association of Petroleum Geologists (AAPG)

Eastern Mexico has been one of the most prolific and most complex regions of the world, and many believe there is still great potential for undiscovered giant and super-giant fields. Welcome to an interview with Stephen Cossey, whose work in eastern Mexico, both onshore and offshore, are pointing to exciting new potential.

What is your name and your relation to geology?

My name is Stephen Cossey (Steve) and I am a consultant and deepwater sedimentologist. I have been consulting for over 22 years and previously worked with BP and Conoco. I obtained my BSc from the University of Wales and MSc and PhD from the University of South Carolina.

What has been your focus in the last several years?

Lately I have been working a lot in Mexico (onshore and offshore) but have also completed projects in Peru, Myanmar and Nicaragua. I have been working part-time for 3 years with a small team in Uruguay which has built up an exploration company in South and Central America. I have also have been updating my database of worldwide deepwater fields and reservoirs which will be available on the web before the end of the year. I recently published a paper (with several authors) in the Interpretation Journal (February 2016) on the fieldwork which we have completed in eastern Mexico.

Please describe some of your field work.

In 2004 I started doing fieldwork on the Chicontepec Formation in eastern Mexico and developed a deepwater clastics field course in the area. We took many oil companies there in the years 2005-2012. I also worked on a project in 2008 where we studied the entire outcrop belt of the Tampico-Misantla Basin. Then I returned to do some personal fieldwork in 2015 on a unique outcrop at the erosional Paleocene/Eocene unconformity where an oil seep is preserved. The outcrop was very small so we excavated all of it and discovered it is very analogous to the oil seeps along the cliffs in Carpinteria, California. We have also studied other outcrops at the Paleocene/Eocene boundary in the Chicontepec area. I have also accompanied several students from the University of Oklahoma into the field when they have been studying the area for a Master's thesis or PhD dissertation.

What have been some of your major insights / revelations?

At the bitumen bed (oil seep) outcrop, we discovered that the bed was deposited along the Paleocene/Eocene erosional unconformity and interpreted it to have been deposited in a subaerial environment. This is interesting because it is overlain and underlain by bathyal turbidites and implies that a sea-level drop of over 200 meters occurred in a very short period of time as no shallow water facies were observed. We believe the sea-level fall was of the order of 1000 to 2000 meters due to the isolation and evaporation of the Gulf of Mexico at about 56 Ma. After an isolation period of probably less than 1 Ma, we believe the Gulf of Mexico catastrophically refilled. We have also found evidence of paleo-karst horizons where bathyal sediments have been karstified. Recently, we interpreted a salt core from a well in the Veracruz Basin as Paleogene in age.

How do they apply to exploration and development efforts?

There are many exploration implications. Large volumes of sediments would have been transported into the basin at this time and karsted horizons would have developed on any exposed carbonate areas. Trap seals would have failed due to the reduced overburden pressures and may contain hydrocarbons from multiple filling phases. In addition, fluvial sediments and evaporates may have been preserved much closer to the center of the Gulf of Mexico than previously thought.

Do you have plans for the future?

Our plans are to return to the field in eastern Mexico in 2017, after we have analyzed the results of our samples from the May 2016 fieldwork. We have excavated all of the bitumen bed and will now concentrate on what we believe are the post-refill canyon-fill sequences and other outcrops across the Paleocene/Eocene boundary.

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