2. ?????????? ??????????????: ??Inherited Heterogeneity + Deformation Bands ??

Let’s look at the composite image, an example from the scale of m-cm to mm of deformation bands. Unit: Bajo Barreal Formation in the Cerro Colorado de Galveniz outcrop.

In the previous post Scale Matters 1 we see how in a regional view of an extensional fault (equivalent scale of seismic in the subsurface) we can miss a lot of details of our reservoir. And as we look closer we find out discontinuities causing grain reorganization, rotation, and in the same cases cataclasis (deformation bands: DB).

So now let’s see the air permeability measurements in the protolith (not affected by DB) and in the deformation bands. What did we find? What are the values are telling us??

• First of all, it is worth it to mention that the reservoir already has variations in grain size, sorting, and matrix content. So, depending on which part of the fluvial architectural element and facies we measure, the K (mD) values we obtain. See the upper right photo: Conglomeratic sandstone (Gst) has 1 order of magnitude higher on K (mD) than the sabulitic sandstone (Sgt).
• In general, most of the DB involves a reduction in permeability. The K measurements of the Shear DB are 1 or 2 orders of magnitude lower than the protolith. And, particularly lowest in the Cataclastic DB (Cat: K 78.2 mD).
• The K varies along the bands. There are also some K values of the deformation bands greater than the permeability in the protolith. An even some variations along band clusters. As we can observe in the microscope photo, in the dilatation DB a conduit has been created, moreover an enhancement of the K measurement value.
• So having dilation Deformation bands might sound like a good thing. However, through geological history, the conduit can be cemented and be a more effective barrier to fluid flow than the Shear DB.?
• And last but not least, we have to consider what type of fluid the reservoir has, what is its density, and viscosity. What order of magnitude— in terms of K (mD) is critical for the fluid not to flow?

Many insights, many questions definitely ?? Outcrops are a great source of Food-for-Thought.

?????? ?????? ???????? ?????????????? ?????????????? ????????????? ?????????? ??t.

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Thank you very much to Facundo Méndez and Allard José Oscar for the photos, you can see more in detail about their work soon. ?? They will be presenting more results at the IAPG Conexplo Congress.

And looking forward to reading more publications about this great analogue that will be carried out by José Allard.

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#exploration #deformationbands #geology #reservoir #oilandgas