Thinking in Pre-Salt? Look to carbonates

May 1, 2013

Over the last decade, the term “Pré-Sal” or Pre-Salt in English has crossed the mind of almost every oil and gas professional in Latin America.

The term gained popularity in 2006 when Petrobras and its partners announced an important oil discovery off the coast of Rio de Janeiro. In a well called Tupi drilled in the Santos Basin at a depth of approximately 5,000 meters from the water line, signs of oil were found under the salt layer. This success led to the drilling of seven more wells, all of which found oil deposits. The investment paid off and led to what is now referred to as the Pre-Salt. So why is Pre-Salt so important?

In the Santos Basin alone, it was initially estimated that the Pre-Salt had 5 to 8 billion barrels of oil equivalent of recoverable reserves. Today’s estimates indicate that the Pre-Salt has placed Brazil among the top 20 major reserve holders in the world and second in Latin America, with almost 14 billion barrels of oil in proven reserves. The value and importance of the Brazilian Pre-Salt is evident, the question is, what are the challenges?

Petrobras is by far the most experienced Operator in the Pre-Salt and has heavily invested in its development. In their own words, the Pre-Salt presents multiple challenges associated with geography, drilling, completion and investments. Beyond the geographical and investment challenges of offshore drilling, is the fact that the Pre-Salt target formation is a heterogeneous carbonate with low permeability and porosity. Carbonates are typically the reservoir rock, where the oil and gas is trapped once it has migrated from the source rock. The completion/production challenge is, how do you get it out?

Because the Pre-Salt is a heterogeneous carbonate, it requires of some type of formation treatment in order to achieve successful production. Acidizing, fracturing and a combination of both have all been tested with successful results; however, due to the complexity of the reservoir, no specific treatment has proven to be the optimal solution. So the question is, if you aren’t certain about the best way to stimulate your well, how do you plan your completion?

The equipment for a well completion provides the path through which hydrocarbon production is taken to surface and ultimately delivers return on investment. Completion design is typically planned months in advance, as the tubulars and downhole tools are tailor-made for a well. In most cases, however, the stimulation technique can be defined well in advance. Therefore, the completion solution that Operators should adopt is one that will have the versatility to allow both acid and/or fracturing operations.

Brazilian innovation has once again recently brought this to life. Over the last few years, one of Brazil’s major Operators has devised and implemented an innovative completion for carbonates in the Campos Basin. The system combines a series of high performance packing elements and premium well screens allowing individual zones to be isolated and treated, in addition to reducing solids production. This system was designed to be the foundation of the optimal completion technology for the Brazilian Pre-Salt. Its versatility and modular design offers Operators the flexibility to acidize and/or hydraulic fracture the well, with the added benefit of open hole, which capitalizes on production contribution from the entire wellbore.

So, if you are thinking about Pre-Salt, drilling through the salt is certainly a challenge, but the real challenge lies in producing the carbonate beneath, and the revolutionary technology to do so successfully is in one of Brazil’s most prolific wells today.