Matrix Acidization

After some time of production, when production rate decreases below our expectations, then we can say that, there is problem in our well.

We diagnose our well for problem, whether problem is in our tubing or inside reservoir ?

If we have tubing problem, like paraffin disposition, then we can remove it by Hot oil circulation or we can do, mechanical scraping with mechanical cutters.

When we have problem in reservoir, then we can not do direct mechanical scraping or cutting.

(Its obvious, we can not go at nano to micro pore levels to do scrapping.)

So, we do it by other means.

If we find, it is reservoir problem, then we do further study to identify exact problem.

 If problem found out is, choking of pores due to any rock materials or solids, then then we can not do direct mechanical scraping or cutting.

(Its obvious, we can not go at nano to micro pore levels to do scrapping.)

So, we do it by other means. We have two options to remove this formation damage.

First is, Acidization and second is, Hydraulic fracturing.

In hydraulic fracturing we creates new flow paths. So, we bypass the problem of damage.

And in matrix acidization (a type of acidization), we introduce acid to formation, which will go through nano to micro level pores (due to pressurized injection of acid) and will remove blocking chemically.

So, in matrix acidization, we inject acid of predetermined concentration and predetermined compositions, at pressure less than fracture pressure of rock.

So, it will not fracture the rock.

Acid will go inside reservoir rock and it will dissolve blocking material (which is blocking our pores or blocking our oil flow).

So, here main thing of heart is, our acid. We have to choose it very carefully for treatment, because if it is selected wrong or it is incompatible with formation, then it can lead to more formation damage also.

Apart from matrix Acidization another one type of acidization is, acid fracturing.

We use matrix Acidization for sandstone rock generally and acid Fracturing for carbonate rocks only.

Important factors for selection of treatment type and Design process:

1) Type of formation (Formation type determines the type(s) of acid necessary )

2) Permeability of rock. (formation permeability determines the pressure required for pumping the acid into the formation.)

1) Type of formation:

In carbonate formations, the acid job design is typically based on the use of hydrochloric acid (HCl) (To dissolve carbonate based materials to create new or clean existing pathways or channels).

In sandstone formations, the acid job design is typically based on the use of hydrofluoric acid (HF), also known as mud acid, in combination with HCl. (Sandstone minerals (sand (quartz), feldspar, and clay particles) are not appreciably soluble in HCl alone but are much more so in mixtures containing HF).

Most simple acid job designs use blends of HCl and HF to respond to the heterogeneous nature of geologic formations.  The strengths of the acids and their volumetric ratios (HCl:HF) are based on the detailed mineralogy of the formation being treated. 

Other additives that are commonly used in an acid job:

Corrosion inhibitor: to protect the well tubulars and related equipment that is exposed to the acid

An emulsion blocker (surfactant): to prevent formation of oil-water emulsions, 

An “iron-control agent”: to retain any dissolved iron (e.g., rust) in solution.

2) Permeability of rock:

Lower the permeability (<0.1mD), the higher the pumping pressure (Generally, above fracture pressure of rock, so we will have conduit to flow of acid, ''Acid Fracturing'').

High permeability (>10 mD) formations the acid can be pumped into the matrix of the formation at relatively low pumping pressures. (Generally, “matrix acidizing'').

For Selection Criteria of well stimulation, click here.

  

Click on icons to follow Us.