The Santos Basin still has a lot in store

Production in the giant pre-salt province of the Santos Basin only started with the Tupi field about 10 years ago. In the years since, it has grown into one of the most prolific basins in the world, delivering almost 2.3 million boe/d in December 2020 (around 1.8 million bpd of oil and about 85 million m³/d of natural gas, or roughly 65% of Brazilian production). 

It is amazing to look back now, knowing the long and winding road that brought us here. Exploration in the Santos Basin actually dates back to the 1970s, with the drilling of more than 80 exploration wells in the three decades that followed. After so much effort and so little to show for it, it looked like it had all been for not.  

Meanwhile, Petrobras had made major discoveries in the giant Tertiary and Upper Cretaceous turbidite sandstone reservoirs of the neighboring Campos Basin. So, in hopes of mitigating future exploration risk in Santos, an intense drilling campaign targeting the bright spots within sandstone turbidites of the Upper Cretaceous drift/post-salt sedimentary wedge was kicked off in 2001, with another 77 exploratory wells drilled up to 2005. However, this turbidite sandstone paradigm dominated the entire campaign, leading to failure after failure, with only three notable discoveries ever being made in the turbidite sandstones of the Santos Basin.  

Eventually, with better seismic imaging and new advanced biomarker technology (applied to oil samples from Santos, Campos and Espirito Santo), this dominant paradigm slowly started to shift. It was now undeniable that almost all the hydrocarbons found in the turbidite post-salt reservoirs of the Campos and Santos basins were actually sourced from the previously well-documented lacustrine pre-salt source rock system. It was finally time to go deeper! 

After drilling one more unsuccessful well in the pre-salt section of the Parati prospect, oil was finally found in the pre-salt carbonate reservoirs in 2006, setting the stage for the giant Tupi discovery. From there, it was off to the races!

Fast forward to present day, and we find ourselves at a similar crossroads. All the success in the Santos Basin to date has been strictly limited to what has come to be known as the “Picanha”, or sirloin, of the inboard area. Exploration in the outboard has really just begun. Athough some might even say that it got off to a rough start with wells 1-BRSA-1363-RJS (Peroba Block) and 1-SHEL-33-RJS (Saturno Block) coming up short, we here at BPS beg to differ. Considering the long road that brought us here, we need to remember that the Santos Basin never gave it up easy. It has truly been a case of No Pain, No Gain! 

In fact, the most important thing we learned from these two most recent wells is that similar elements and processes of the petroleum system present in the inboard could indeed exist in the outboard province. With the 17th Bidding Round fast approaching, the key question is how far the pre-salt mid to late Aptian lacustrine hypersaline (Sag) and upper and Lower Barremian (Rift) lacustrine saline to brackish source and the Aptian microbial reservoir systems extend beyond the limits of the already well-understood “Picanha” comfort zone (Figure 1).

 

Figure 1. Map of the Santos Basin showing post and pre-salt production fields, sectors/ exploration blocks to be offered in the 17th Bidding Round and the location of the satellite images and recently-drilled wells in the Peroba and Saturno blocks (source: ANP Boletim, 2020). Note the limits of the pre-salt “Picanha “area, considered to be the inboard comfort zone for exploration in Santos Basin. Most of the sectors being offered are situated in the outboard area where no wells have been drilled to date.

Enter BPS. After spending the better part of the last year working on a series of state-of-the art PSM studies of the inboard and outboard Santos Basin, we can confidently say that there is oil out there, potentially to the tune of 100 billion boe. The meaning might have changed slightly, but it’s time to say it again. Let’s go deeper! 

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