Selection criteria for well stimulation

Question is, when we use hydro fracturing treatment and when we use matrix Acidization treatment ?

Answer is, when we have very low permeability from initially, and if we do only matrix acidzation, then it will only give us that low initial permeability back only. And if we do hydraulic fracturing, then it can give us more permeability than earlier.

So, if our reservoir is having less than some threshold value of initial permeability, than we go for hydraulic fracturing.

And if we have initial reservoir permeability greater than some values, than restoration of that permeability can also will lead to more production. So we go for matrix acidization, if we have good initial permeability.

When we use matrix Acidization and when we use acid Fracturing ?

We decide based on lithology first.

We use Acid Fracturing in Limestone or Carbonate reservoirs only. And matrix Acidization is generally used in sandstone reservoirs.

Another view of answering is, in low permeability reservoirs, we have to inject fluid at high pressure (Darcy's law).

So generally injection pressure exceed the reservoir fracture pressure and treatment will be acid Fracturing rather than matrix Acidization.

And in high permeability reservoirs, we can inject acid at ease. So we will have comparatively lesser injection pressure.(less than fracture pressure of rock)

So, we use matrix Acidization treatment here.

When we use Acid Fracturing and when we use Hydro fracturing ?

In sandstone reservoirs, we can not do acid Fracturing. So we go for hydro fracturing (only) for sandstone reservoirs.

So, for sandstone reservoirs, we have two options,

1) Matrix Acidization (if initial permeability is high enough)

2) Hydro Fracturing (If initial permeability is lower.)

Generally, We go for Acid Fracturing in Carbonate reservoirs.