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PTPR-370-D > Module 7: Acid Stimulation > Flashcards

Module 7: Acid Stimulation Flashcards

1
Q

What is stimulation?

A

the act of either removing the skin damage (matrix acidizing) or bypassing the damage and creating a negative skin (hydraulic fracturing)

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2
Q

When referring to acid stimulation or matric stimulation, are the injection pressure above or below the fracture pressure of the formation?

A

BELOW

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3
Q

Name 6 types of damage that acid stimulation can attempt to remediate?

A
  1. Clay
  2. Paraffin Asphaltenes
  3. Emulsions
  4. Wettability Issues
  5. Scale
  6. Particulate damage
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4
Q

When does the presence of clay become an issue in a reservoir?

A

if it is present in large enough volumes and will react in a a detrimental manner to the fluid flowing through the pore space.

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5
Q

What are the 4 most common clays that account for most the of the formation damage seen in oil and gas wells?

A
  1. Kaolinite
  2. Smectite (montmorillinite)
  3. Illite
  4. Chlorite
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6
Q

What kind of formation damage can be seen from Kaolinite clay?

A

large particle sizes and does not bond well to host grain, making It a migrating and plugging issue

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7
Q

What kind of formation damage can be seen from Smectite Clay?

A

swelling problems, sensitive to water. High micro-porosity that traps migrating particles and binds water to the host grain.

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8
Q

What kind of formation damage can be seen from Illite Clay?

A

same as smectite and also fibres can trap micro size debris and may also break off and migrate.

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9
Q

What kind of formation damage can be seen from Chlorite clay?

A

serves as a collection point for migrating debris and contains high levels of iron which may precipitate as iron hydroxide.

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10
Q

When are paraffins and asphaltenes deposited?

A

during the production of crude oil

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11
Q

How is the precipitation of paraffins triggered?

A

loss of pressure, loss of temperature and/or loss of light end hydrocarbons.

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12
Q

Where is the most common are for the precipitation of paraffins?

A

production tubing. But can also form on the perforations in cases where nearby pressure-depleted reservoirs experience dry gas cycling.

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13
Q

What are the 3 common forms asphaltenes are found in?

A
  1. Hard coal like substance
  2. Blackened sludge or rigid film emulsion
  3. In combination with paraffins
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14
Q

What leads to the precipitation of alphaltenes?

A

anything that takes away the resin or breaks the stability of the micelle.

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15
Q

What is an emulsion and what does it consist of?

A

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).

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16
Q

What are some common solids that stabilize emulsions?

A 
Silt
Sand
Clays
Cuttings
Metal flakes
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17
Q

What is wettability?

A

the fluid type and behaviour of that fluid that coats the grain of the formation and acts as its connate saturation component.

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18
Q

Formation’s wettability can be?

A

Water-wet
Oil-wet
Neutral

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19
Q

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?

A

Water-wet

Achieved by using surfactants

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20
Q

Will change to wettability affect ultimate recovery and relative permeability?

A

YES!!

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21
Q

When does scale usually occur?

A

from the mixing of incompatible waters

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22
Q

What are the 3 most common scales?

A
  1. Calcite
  2. Calcium sulfate
  3. Barium Sulfate
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23
Q

How can the 3 scales be removed?

A

calcite- HCL
Calcium sulfate- not removed by acid
Barium sulfate- mechanical removal is necessary

24
Q

What is particulate damage?

A

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.

25
Q

Name 4 methods of diagnosing damage?

A

DST
Inflow Performance Analysis
Fluid Analysis
Reservoir Logging methods

26
Q

What 3 things should you ensure you eliminate as possible well performance failure prior to considering an acid stimulation?

A
  1. Artificial lift method correct
  2. if the well is a water injector, is it possible that hydrocarbons could have been injected causing emulsion or phase blocking
  3. is there fill covering the producing interval
27
Q

What are the 2 kinds of acid stimulation?

A

Matrix acidizing

Hydraulic fracture stimulation

28
Q

Matric acidizing will succeed in doing what to the skin S=?

A

S=0, will only return the skin to neutral state and will not aid in yielding stimulation

29
Q

What happens when skin damage is present in a well?

A

it causes additional pressure drop in the system which would not appear if the well was undamaged.

30
Q

The radius over which the skin occurs is usually small, how small?

A

up to 10cm

31
Q

What is the typical skin factors range?

A

50(very badly damaged) to -5 (stimulated well). It is impossible for a skin factor to be less than -8.

32
Q

What 2 ways can wellbore radius be increased?

A

underreaming or fracturing

33
Q

Why is acid stimulation without fracturing favourable?

A

increases permeability of the reservoir near the wellbore by removing any part of the grain cemetation that is acid soluble.

34
Q

In general, what 4 things are acid stimulation suitable for?

A
  1. High permeability rocks that incurred damage during drilling, completion or production
  2. Very soft, unproppable formations
  3. Very thick acid soluble zones
  4. Supplementing a hydraulic fracture treatment.
35
Q

What are the 4 acids used in oilfield applications?

A 
Hydrochloric acid (HCL)
Hydrofluoric-hydrochloric acid blends (HF-HCL), known as MUD ACID.
Acetic Acid (CHCOOH)
Formic Acid (HCOOH)
36
Q

What is the most common acid and what kind of formations does it react with?

A

HCL, reacts with limestone and dolomite

37
Q

What formation is mud acid commonly used in?

A

sand reservoirs

38
Q

Why is HF-HCL acid blend known as mud acid?

A

because it works well at eliminating damages caused by mud filtrate invasion during drilling.

39
Q

Formic and acetic acids are known as what and are used why?

A

organic acids and are used because of their slow reaction times and ease of inhibition. Commonly used with HCL.

40
Q

The design of acid additive systems depend on what 5 things?

A
  1. Temp
  2. Formation
  3. Rock type
  4. hydrocarbon trap
  5. damage mechanism
41
Q

Name 6 acid additives

A
  1. Corrosion inhibitor
  2. Surfactants
  3. Mutual solvents
  4. Alcohols
  5. Anti-sludge additives
  6. iron control/clay control
42
Q

corrosion increased as acid strength increases? T or F?

A

TRUE

43
Q

Corrosion inhibitors work to form a barrier on tubular surfaces which interferes with what?

A

electrochemical reactions

44
Q

Why are surfactants used?

A

to change or maintain wettability by controlling surface and interfacial tension

45
Q

What are the 3 types of surfactants, explain

A
  1. Anionic- used as a non emulsifying, retarding and cleaning agent
    2, Cationic- used as non-emulsifiers, corrosion inhibitors and bacteriacides
  2. Nonionic- used as a non emulsifiers and foaming agent
46
Q

Why are alcohols considered a cost effective alternative to surfactants?

A

have surfactant type qualities, can reduce the amount of water in a formation

47
Q

What do anti-sludge properties prevent?

A

negative reaction between acid and crude oil that cause heavy end precipitate which can be permanent.

48
Q

Does iron accelerate or retard sludge formation?

A

accelerate and stabilizes emulsions

49
Q

What are some specialty acids used for carbonate stimulation and why are they used?

A

Foamed acid- used for fluid diversion or for acid fracturing
Emulsified Acid- used to increase viscosity for fracturing
Surfactant Gelled Acid- Used for acid fracturing

50
Q

What 4 things to design acid treatments include?

A
  1. Tubing Pickling
  2. Acid washes
  3. Matrix acid jobs
  4. Acid diversion
51
Q

Why is tubing pickling used?

A

to remove iron, pipe dope, scale, etc from tubing prior to injecting acid into the zone

52
Q

Can Pickle acid come in contact with the formation?

A

NOOOO

53
Q

Why are acid washed used?

A

to was acid soluble residue or scale from pumps or tubulars.
to wash perforations to clean up damage from perforating

54
Q

Why are matrix acid jobs used?

A

removes near wellbore damage, treat zone that cannot be perforated

55
Q

In a matrix acid job, acid is injected in to the zone above or below fracturing pressure?

A

BELOW

56
Q

Why are acid diversions used?

A

to deliver live acid to a larger area of the formation and to provide deeper penetration into the formation

57
Q

Name 3 typical diversion agents?

A 
ball sealers (temporarily plug the perfs)
chemical diverters (benzoic acid, naphthalene and rock salt)
foam fills

PTPR-370-D (4 decks)

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