Edgar Rangel
View from the Top

Enhancing Oil Recovery at Cantarell

Tue, 01/22/2013 - 14:10

Q: What should the future of Cantarell look like, and what are the most suitable technologies to be applied there to optimize production and recovery rate?

A: We have to make clear that Cantarell is a complex of different fields. It might often be seen as a project, an asset, or an account in the eyes of the Ministry of Finance, but in reality it is a set of fields, with the main field being Akal. When people assert that production at Cantarell has stabilized, in reality they mean that the Cantarell asset has stabilized, because some of its fields, such as Sihil, have increased production, while production at the Akal field has gone down. Historically, when we spoke of Cantarell, we referred to Akal, but output at that field has been declining for almost a decade and is expected to continue doing so, while production at Sihil and other smaller fields has increased. However, the Cantarell asset still has substantial reserves. It ranks number two in terms of proved reserves and number three in terms of 2P reserves, so it is an important mature field.

With an original volume of close to 30 billion bbl of oil in place, Akal is the most important field of Cantarell. In 1979, 60% of that volume was located in the matrix system – the solid parts of the rock – and 40% in the fracture system. Many years later, we have produced almost half of the original oil in place, but most of this came from the fractures, so currently 90% of the remaining oil is in the matrix and 10% is in the fractures. Thus, we do have a lot of oil remaining in Cantarell, but Pemex needs to expel the oil from the matrix system or “wash the rock,” and the way to do this is by means of injecting gases and chemicals, such as C02, natgas and surfactants or polymers. We at the National Hydrocarbons Commission (CNH) strongly believe that this requires complex Improved Oil Recovery (IOR), as opposed to simply Enhanced Oil Recovery (EOR). This entails a broader range of activities, such as acquiring new seismic data, running modern well logs, and performing reservoir engineering analyses to assess where most of the remaining oil is located in areas that have been partially drained, areas that are being cyclically refilled by gravity drainage, and areas that have been the least produced. Oil has been extracted from different blocks within the field, so Cantarell has been drained unevenly; some areas are relatively dry and others have a lot of oil. CNH recommends a series of recovery measures. New techniques now permit increased recovery when drilling unconventional wells. By using smart completions, you can place the tubing of producing wells in the “oil window,” you can also isolate “bad fractures” that are either pulling gas from the cap or water from the aquifer, and perform a variety of other activities to optimize the production of liquid hydrocarbons. In a project management program, using these tools will help to raise the recovery efficiency. We do believe that through all these IOR-EOR activities, it is possible to keep Cantarell’s production stable for several decades.

Q: Pemex officials say that production at Cantarell has stabilized. Yet, production numbers indicate this is not yet the case. Where will production stabilize?

A: It will stabilize once Pemex has implemented all these recovery enhancement strategies that collectively make up what we call IOR-EOR. For many years, Pemex has been basically draining the reservoir like a tank. But when the gas-oil contact or the oil-water contact reach the depth of producers, E&P needs to shut down these wells because they start producing significant amounts of gas or water. If you shut many wells per year and you do not replace them, production naturally decreases. Without a sufficient number of producing wells, there is nowhere to get the product from. If you just go and empty the tank - which is what has been occurring in Cantarell – and then you open the valve, you know that the tank has a lot of oil there, but nothing will come out, because you left most of the oil trapped in the solid parts of the rock.

We, as a regulator, have to be strong enough or intelligent enough to convince Pemex that the techniques mentioned will work. Otherwise, Pemex will continue using its current development plan, just draining fields and forgetting about the remaining oil. We need to persuade Pemex that it can both produce the reservoirs in an economic fashion and manage the remaining oil in a more modern way. They are already doing some pilot projects; learning about unconventional drilling with smart completions and studying the applicability of IOR-EOR.