The 5 Magic Parameters for Oil Accumulation: Nigeria’s Chad Basin Experience

I offer this as a follow-up piece to my article titled “Oil in Nigeria’s Chad Basin: A Deepening Dilemma” which was originally written for the July 2012 newsletter of the Young Earth Scientists (YES) Network of the Geological Society of Africa. Although the article in question was initially meant to be published only for the benefit of fellow YES Members, who by default, subscribe to the YES Network newsletter, I would later feel the need to spread out its readership by publishing the same piece in both print and online national dailies in Nigeria.

As it was, the ensuing wider reach of the article would generate some little responses from everyday journal readers. I therefore received with delight, responses from professionals that vary from academics in the earth sciences to industry-based professionals, and to professionals-turned-politicians. Each of them has sought to know more on the so-called five magic parameters for oil accumulation in the Chad Basin area of Nigeria. Here it goes:

Source rock: The Gongila formation or Fika Shale can serve as a potential source rock for petroleum accumulation in the Chad Basin based on its Total Organic Carbon (TOC). The TOC of the Gongila Formation which is rated at 1.2wt percent, and that of the Fika Shale is rated at 0.9wt percent.

Reservoir rock: Some geologists are wont to believe that following its stratigraphic position and its lithology, not only the Gombe Sandstone can be a reservoir rock; the Kerri-Kerri Formation can be a suitable reservoir rock too.

Geothermal temperature: The depth of burial of the source rock can be said to be as deep as 300 meters, a reasonable depth at which the requirement to convert organic matter into petroleum is plausible (60 to 120 degrees centigrade). The temperature gradient of the Chad Basin is said to be increasing by a degree centigrade per a hundred meters with a surface temperature average of 35 degrees centigrade. It is believed that the source rock of this basin falls somewhere between 65 to 70 degrees centigrade as per geothermal temperature.

Migration pathway: Based on the preceding parameters (above), it is believed that hydrocarbon have been generated in the Chad Basin area of Nigeria. The Chad Basin is believed to have experienced a series of tectonic activities that resulted into series of faults probably during the Jurassic as a result of the splitting of Gondwanaland. These are favorable conditions that can serve as suitable migration pathways for accumulated hydrocarbon.

Trap: Hydrocarbon traps in the Chad Basin can be as a result of both Santonian folding or Jurassic rifting that has resulted into faults.

Conclusion: It is reported by Klemme (1986) that 35 percent of rifted basins are productive. While Kingston et. al (1983) reported that 49 percent of poly-historic basins are productive worldwide. The Chad Basin qualifies as both rifted and poly-historic. It is therefore possible that based on the above evidences, hydrocarbon might have occurred in the Chad Basin area of Nigeria. Although it must be noted that there is a bit of a controversial subject associated with the basin’s productivity—the presence of some volcanic intrusions; is a notable factor which might degrade the organic matter. But by and large, there is the need for further research, to help evaluate in detail, the hydrocarbon potentials of the Chad Basin area of Nigeria.

Corrigendum: I mistakenly wrote in my previous piece, “Oil in Nigeria’s Chad Basin: A Deepening Dilemma” (page 8 of the July 2012 YES Network Newsletter) that geothermal temperature of between 120-150 degrees centigrade supports oil formation. To put it correctly, the oil formation window falls between 60 to 120 degrees centigrade. The implication of this is palpable to a beginning student of petroleum geology. The error is therefore regretted.

By Mohammed Dahiru Aminu

Mohammed Dahiru Aminu, wrote from London, United Kingdom. He can be reached at mohd.aminu@gmail.com