Friday, February 12, 2016

Fractured Reservoir, Our Future

Naturally Fractured Reservoir is a term that we use to the reservoir that  the fracture have significant contribution to the change of the reservoir's permeability.With these fractures, there are others properties which will change too, such as flow rates, anisotropy, recovery, and storage. It is a kind of confusing material for many people, as until this day, people always prefer the conventional reservoirs which have been been developed and observed for hundred years. People simply don't know the fact that more than 50% of proven reserve in the world are obtained in Naturally fractured reservoir. Even almost all the geothermal reservoirs are naturally fractured reservoirs. Yes they are more complex and heterogeneous, but as the world need energy to develop the modern civilization, the advancement of technology to the more complex and multiple porosity reservoirs is a must. That is why our future will move towards the development of this fractured reservoir. While other form of energy (renewable energy) is still far too expensive (and perhaps won't be a cheap choice for the next years), the development of this unconventional reservoir is still cheaper, although it is not as easy as the conventional one.

There are several fields which are categorized as naturally fractured reservoir such as:

  1. Pina Field, Republic of Cuba (light oil)
  2. Purwakarta Field, Indonesia (CBM)
  3. jatibarang Field, Indonesia (CBM)
  4. Jatinegara Field, Indonesia (CBM)
  5. Ain Zalah Field, Iraq (oil)
  6. Kirkuk Field, Iraq (oil)
  7. Gela Field, Sicily (heavy oil)
  8. Elk Hills Field, USA (heavy oil from fractured shale)
  9. Santa Maria Field, USA (heavy oil from fractured shale)
  10. Big Sandy Gas Field, USA (gas from bituminous shale)

As it can be seen above, the content of the fractured reservoir might be different, and it is more to show the type of reservoirs which are dominated by fractures as their properties. Among other properties that should be remembered, the fractured reservoir have the main characteristic that the fracture will be the avenue for fluid flow and the matrix (rock pores) as the storage. In some fields, such as Ain Zalah Field, have very low permeability that it is impossible to flow the fluid inside the reservoir. This condition was not attractive, if we never consider the effect of the fracture. The effect of fracture as wide as 1 millimeter may produce oil as much as 7000-10000 BOPD (Braunstein 1953)! That is why the production of this kind of reservoir rely on the network of the fractures inside.As long as the fractures have the communication, the reservoir can be productive.  

Nelson classify this reservoir based on the fracture's effect to the reservoir properties:

  1. Type 1: Fractures provide essential porosity and permeability to reservoir
  2. Type 2: Fractures provide essential permeability to reservoir 
  3. Type 3: Fractures provide a permeability  assist to reservoir

then, talking about how the geologist could identify the reservoir, it is very important for them to find the outcorp of the fractured reservoir. Basically, the fracture will be created of either tectonic effect, regional effect, contractional, and surface-related effect. thus, the size could be as small as a compas and as big as a regional area. The finding of the outcorp doesn't guarantee the productivity of the reservoir. There are a lot of other things that should be considered such as is the reservoir produce/trap oil or not; or is the fracture filled with other mineral or not and so on. Basically, we may say that the fractured reservoir give more challenges, but the result will be worth it for human development.

Any suggestion, additional info, or input? please kindly write in the comment section. Thank you.


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Irianto Petrus Binsardo
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