Module 7: Acid Stimulation Flashcards
What is stimulation?
the act of either removing the skin damage (matrix acidizing) or bypassing the damage and creating a negative skin (hydraulic fracturing)
When referring to acid stimulation or matric stimulation, are the injection pressure above or below the fracture pressure of the formation?
BELOW
Name 6 types of damage that acid stimulation can attempt to remediate?
- Clay
- Paraffin Asphaltenes
- Emulsions
- Wettability Issues
- Scale
- Particulate damage
When does the presence of clay become an issue in a reservoir?
if it is present in large enough volumes and will react in a a detrimental manner to the fluid flowing through the pore space.
What are the 4 most common clays that account for most the of the formation damage seen in oil and gas wells?
- Kaolinite
- Smectite (montmorillinite)
- Illite
- Chlorite
What kind of formation damage can be seen from Kaolinite clay?
large particle sizes and does not bond well to host grain, making It a migrating and plugging issue
What kind of formation damage can be seen from Smectite Clay?
swelling problems, sensitive to water. High micro-porosity that traps migrating particles and binds water to the host grain.
What kind of formation damage can be seen from Illite Clay?
same as smectite and also fibres can trap micro size debris and may also break off and migrate.
What kind of formation damage can be seen from Chlorite clay?
serves as a collection point for migrating debris and contains high levels of iron which may precipitate as iron hydroxide.
When are paraffins and asphaltenes deposited?
during the production of crude oil
How is the precipitation of paraffins triggered?
loss of pressure, loss of temperature and/or loss of light end hydrocarbons.
Where is the most common are for the precipitation of paraffins?
production tubing. But can also form on the perforations in cases where nearby pressure-depleted reservoirs experience dry gas cycling.
What are the 3 common forms asphaltenes are found in?
- Hard coal like substance
- Blackened sludge or rigid film emulsion
- In combination with paraffins
What leads to the precipitation of alphaltenes?
anything that takes away the resin or breaks the stability of the micelle.
What is an emulsion and what does it consist of?
combination of 2 or more immiscible fluids that will not molecularly disperse into one another. consists of an inside phase and an outside phase (interface).
What are some common solids that stabilize emulsions?
Silt Sand Clays Cuttings Metal flakes
What is wettability?
the fluid type and behaviour of that fluid that coats the grain of the formation and acts as its connate saturation component.
Formation’s wettability can be?
Water-wet
Oil-wet
Neutral
In order to recover the most hydrocarbons, it is the aim of most treatments to change the formation wettability to and how is this achieved?
Water-wet
Achieved by using surfactants
Will change to wettability affect ultimate recovery and relative permeability?
YES!!
When does scale usually occur?
from the mixing of incompatible waters
What are the 3 most common scales?
- Calcite
- Calcium sulfate
- Barium Sulfate
How can the 3 scales be removed?
calcite- HCL
Calcium sulfate- not removed by acid
Barium sulfate- mechanical removal is necessary
What is particulate damage?
fines blocking of pore throats is caused by invasion of drilling mud, cements, kill fluids, and dirty water during drilling, completion, and production of a well.
