prediction of reservoir performance using stimulation methods

1. Production
Improvement by
Stimulation Methods
By
Syed Nawaz
Delta Studies Institute
Andhra University

2. Content
Introduction
What is Stimulation ?
When Stimulation
Why Stimulation and types of Stimulation
Well stimulation work process
Types of Stimulation Methods
Matrix Acidizing
Hydraulic Fracturing
References

3. Introduction
What is Stimulation?
Generally it is encouragement of something to make it develop or become more
active.
Well stimulation : any of several operations used to increase the production of a well

4. When stimulation?
Pressure decreases and even production reduces naturally
Reduction in permeability due to overburden stress
Natural low permeability formation
Formation Damage

5. Why Stimulation
Simply to maintain the reservoir or to increase the production or to improve the flow
of HC from Reservoir to wellbore at desire conditions, and the parameters which are
to be maintain are as :
Reservoir pressure
Permeability
Fluid properties

6. Well stimulation work process

7. Types of Stimulation methods
Based on Injection rate of Fluid into the reservoir and pressure of injection or
reservoir the well stimulation techniques are classified into 2 types and they are as
follow:
If Injection rate is below fracture pressure then it is termed as Matrix Acidizing
and
If injection rate is above fracture pressure then it is said to be fracture acidizing

8. First Acid Stimulation in 1932-33

10. Matrix acidizing
The matrix acidizing is applied to remove skin damage caused due to drilling, completion, workover, well killing, or injection fluids and by
precipitation of scale deposits from produced or injected water
During Matrix Acidizing the acids dissolve the sediments and mud solids within the pores
General procedure for conducting Matrix Acidizing operation :
1- Run breakdown tests with oil or water to estimate fracture pressure of a reservoir
2- selection of stimulation process based on pressure estimation
3- clean up of hole prior of stimulation
4- lowered the tool for acidizing into the selected area and connect with pumping unit at the surface
5- start the process of pumping acid into the formation
6- When acid starts entering into the formation, gradually remove the nozzle for complete acidizing over the selected area.
7- Thus acid reduces skin and widened the path of fluid
8- allowing fluid to flow and simultaneously removing the lowered tool

11. Carbonate Rocks
Carbonate rocks are sedimentary rocks composed primarily of carbonate minerals.
The two major types are
limestone, which is composed of calcite or aragonite
dolomite rock (dolostone) which is composed of mineral dolomite.
We should remove carbonate in order to prevent the formation of precipitation due to
the reaction between these chemicals
Calcium and magnesium will behave immiscible when react with hydrochloric acid or
hydrofluoric acid

12. The common acid is Hydrochloric acid (HCL). Concentration is 15-28% for conducting
general stimulation operation. And low concentration HCL is used to clean up the well
Organic acids such as Acetic acid and formic acid are used particularly for high
temperature wells.
In high temperature applications, HCl does not produce acceptable stimulation results
due to its fast reaction that leads to Lack of penetration. Organic acids, like formic or
acetic acids, can be used to offer a slower-reacting and thus deeper stimulating acid[5]

16. Acid Stimulation process

17. Common Acids for Stimulation
Hydrochloric
Hydrochloric-Hydrofluoric
Acetic
Formic
Sulfamic
Fluoboric
Combination of above acids based on situations

18. Problems due to Acid
Create precipitants
Form emulsion
Create sludge
Corrode steel, etc
To avoid these problems additives are being used along with acid. And if water wet formation
then used surfactant for all acid jobs to reduce surface tension and interfacial tension to
prevent emulsions
Anti sludge agents: heavy asphaltic crudes forms an insoluble sludge (resins, paraffin waxes,
high molecular weight HC and other materials) when contacted with acid, so in order to avoid
this addition of surfactants to acid can prevent the formation of sludge
Corrosion inhibitors for acid are chemical additives that reduce the rate of corrosion of steel
by acid

19. Factors that effects the function of Acid
Type of steel including hardness
Temperature
Type of acid
Acid concentration
Acid contact time
Physical and chemical properties of reservoir rock
Flow velocity of acid
Pressure
Area of contact per unit volume of acid

20. Hydraulic Fracturing
The objective of hydraulic fracturing is to increase well productivity by creating a
highly conductive path into the formation.
In this process the sand laden gelled fluid is pump with a predetermined pressure into
the subsurface rock formation to improve the flow into a wellbore.
Mainly for fracking formaldehyde, acetic acids were used, and boric acids, etc and
hydrochloric acid is mainly used to dissolve the minerals in the rock . For a single
fracking process 80-300 tons of chemicals may be used,

21. First Hydraulic Fracturing in 1947

22. Hydraulic Fracturing in OMAN 90’s

23. Hydraulic fracturing in 2000’s

25. Fracturing process
It is done in 3 steps:
First, a pad of fracture fluid is injected into the well to initiate fracturing of reservoir.
Follow by a slurry of fracture fluid and propping agents are pumped down the well to
extend the fractures and fill them with propping agents.
Propping agents or proppants are small spheres that hold open the fractures after
pumping has stopped.
The well is then back flushed in the third stage to remove the fracture fluid

26. Commonly used chemicals and solution
Fracture fluid is a gel formed by water and polymers
Oil based fracture fluid and foam based fracture fluids using bubbles of N2, CO2 can
also be used to minimize formation damage
Citric acid,
Sodium erythobate
Thioglycolic acid, these are used to stop metal from precipitation within the fluid
Polyacrylamide and hydrotreated light petroleum distillate are used to lubricate the
water and reduce friction.

27. References
Running notes by Dr.Hareram Sir (Guest faculty for Delta Studies Institute, Andhra University)
Syed Nawaz (Ex-Student Petrogate Academy, Student of Andhra University)
Society of Completion and Association (Stimulation Expertise)
Oil and Gas Well Testing by Amanath Chowdary
Rigzone
SPE
IRS
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28. Any Queries?