“Down and Dirty“ Field Scale Analysis

This is a procedure used when the Account Representative or the field Technician is called upon to identify scale samples in the field. An operator may need to take immediate steps to remove scale from production tubing, flow lines, or other pieces of equipment, and time does not permit submitting the sample scale to a laboratory for analysis. The PCC personnel must be able to determine where the scale is calcium carbonate, iron carbonate, calcium sulfate, barium sulfate, strontium sulfate, or a combination of scales. The following procedure outlines various methods that the personnel in the field may use to determine the type of scale in question. At the very least, this method of identification will give a reasonable basis for recommending a removal treatment.

Prior to subjecting any scale sample to an analytical procedure, the sample should be rinsed in a solution of xylene to remove any oil coating.

1. Check with magnet to determine if any iron is in the solids. (Strongly magnetic? Slightly magnetic, Not magnetic) If magnetic, then you already know that it is some type of iron compound.

2. Put solid in water. If it dissolves, it’s salt (NaCl). If not, got to step 3.

3. Put solid in 15% HCl. If it violently effervesces (like Alka-Seltzer) with no odor and does not appreciably turn the acid yellowish/greenish, it’s Calcium Carbonate (CaCO3) scale. If not, go to step 4.

4. If it violently effervesces (like Alka-Seltzer), turns the acid yellowish/greenish, gives off “rotten egg” odor, it’s Iron Sulfide (FeS). If it slowly efferveseces, turns slightly yellowish/greenish, gives off slight “rotten egg” odor, turns white while effervescing, it’s Iron Carbonate (FeCaCO3). If not, go to step 6. NOTE: IRON CARBONATE SCALE IS A CORRROSION BY-PRODUCT OF CO2 AND WILL ALWAYS HAVE UNDER-DEPOSIT PITTING!

5. Put solid sample in scale converter. After some time, if it turns into “cottage cheese”, add 15% HCl. If it solubilizes, it’s Calcium Sulfate (CaSO4) scale.

6. If still no reaction, put solid into solvent. If it solubilizes, it’s hydrocarbon (paraffin, asphaltene). (If it burns with lighter, it’s hydrocarbon.

7. If no response from previous steps, the solid is either inert (sand, silica, clay) or Barium Sulfate (BaSO4) or Strontium Sulfate (SrSO4) scale…get to lab.

Soluble in water = salt (NaCl)

Not soluble in water

BUT, when exposed to acid = Violent reaction with HCl = CaCO3

No reaction with water or HCl

Scale converter turns it into an acid soluble sludge

HCl solubilizes acid soluble sludge, i.e. converted scale = CaSO4

Micel solvents, such as PCC Acid Booster, prevents acid emulsions, removes hydrocarbons from acid soluble material, prevents sludge, increases permeability, leaves formation rock “water wet”

Scale Scale in Heavy Sludge

Sludge Coated Scale in 15% HCL + Micel

Approximately 10 Seconds Later

QUALITATIVE ANALYSIS OF SOLIDS

      Soluble in HCL    

ComponentSoluble in Solvent Magnetic Reaction

Acid Color Smell Water Soluble

Hydrocarbons Yes No None None None No

CaCO3 No No Violent None None No

CaSO4 No No None None None NoBaSO4, SrSO4 No No None None None No

FeS No Weak Strong Yellow H2S No

Fe2O3 No No Weak Yellow None No

Fe3O4 No Strong Weak Yellow None No

FeCO3 No No V Strong Yellow None No

NaCl No No None None None YesSand, Silt,

Clay No No None None None No

QUALITATIVE ANALYSIS OF SOLIDS

      Soluble in HCL    

Component Soluble in Solvent Magnetic Reaction Acid Color Smell Water Soluble

Hydrocarbons Yes No None     No

CaCO3 No No Violent None None No

CaSO4 No No None     No

BaSO4, SrSO4 No No None     No

FeS No Weak Strong Yellow H2S No

Fe2O3 No No Weak Yellow None No

Fe3O4 No Strong Weak Yellow None No

FeCO3 No No V Strong Yellow None No

NaCl No No None     Yes

Sand, Silt, Clay No No None     No

Hydrocarbons Paraffin; Asphaltenes

CaCO3 Calcium Carbonate; Calcite

CaSO4 Calcium Sulfate; Anhydrite; Gypsum

BaSO4, SrSO4 Barium Sulfate, Barite; Strontium Sulfate, Celestite

FeS Iron Sulfide

Fe2O3 Iron Oxide

Fe3O4 Iron Hydroxide

FeCO3 Iron Carbonate

NaCl Salt

Sand, Silt, Clay Inerts

Scaling Tendency Calculations

Calcium Carbonate:

Multiply mg/liter of Bicarbonate by the mg/liter of CalciumIf the resulting product is:

Below 500,000 Tendency RemoteAbove 500,000 Tendency PossibleAbove 1,000,000 Tendency Probable

Calcium Sulfate (Gypsum):

Multiply mg/liter of Sulfate by the me/liter of Calcium

Below 5,000,000 Tendency Remote5,000,000 to 10,000,000 Tendency PossibleAbove 10,000,000 Tendency Probable

Cations Anions Other Properties

*Calcium (Ca) *Chloride (Cl) *pH *Magnesium (Mg) *Carbonate (CO3) *Temperature *Sodium (Na) *Bicarbonate (HCO3) *Specific Gravity *Iron (Fe) *Sulfate (SO4) *Dissolved Carbon Dioxide *Barium (Ba)

*Sulfide as H2S Strontium (Sr)

Resistivity Manganese (Mn)

Dissolved Oxygen

Bacterial Population

Oil Content

Turbidity

Suspended Solids – amount, size, shape, chemical composition

The components marked with an (*) are essential to obtaining a thorough and meaningful water analysis.

Table 2 Relative Solubilities of Mineral Scales in Water

Mineral Scale Solubility (mg/L) in Water Calcium Sulfate (Gypsum) -- CaSO4 . 2H2O 2080 mg

Calcium carbonate -- CaCO3 53 mg Barium Sulfate -- BaSO4 2.3 mg

Table 1 Primary Constituents of Oilfield Waters

Table 3 Primary Variables in the Formation of Mineral Scales

Scale, or Deposit Chemical Formula Primary Variables

Calcium Carbonate CaCO3

-Partial pressure of CO2 (scale increases as CO2 decreases)

-Less Soluble with Increasing temperature

-Pressure Drops -More soluble as TDS increases

Calcium Sulfate CaSO4 . 2H20 (dehydrate) CaSO4 (anhydrite)

-Less Soluble with Increasing temperature

-Pressure drops -More soluble as TDS increases

Barium Sulfate Strontium Sulfate

BaSO4

SrSO4

-More soluble as Temperatures increase

-More soluble as TDS increases Iron Compounds:

Iron Carbonate Iron Sulfide

Iron (II) Hydroxide Iron (III) Hydroxide

Iron Oxide

FeCO3

FeS Fe(OH)2

Fe(OH)3

Fe2O3

-Corrosion by-products -Bacterial activity -Dissolved gases

-Depositions increase as pH increases (especially true after an

acid job with spent acids)

Type Hydrocarbons Iron

Compounds Carbonates Sulfates Insolubles/organics

-Oil Carry Over -Iron sulfide -Calcium -Calcium -Formation fines

-Paraffin -Iron oxide carbonate sulfate -Sand Detail Deposition -Iron carbonate -Iron carbonate -

Magnesium carbonate

-Magnesium sulfate -Barium sulfate

-Microbes - Asphaltenes

-Separator -Corrosion -Scaling waters -Scaling water -Inadequate wellbore

malfunction -Incompatible -Corrosion -High cleanouts

-Truck treating waters -Pressure drops temperature -Pump intakes set

schedules -Oxygen -Fluid property -Pump low Probable -Surface tank introduction changes outlets/shrouds -Bacterial activity Origin damages

-Improper equipment sizing

-Stimulation by- products

-Incompatible waters

-Natural, or induced, formation of asphaltenes (CO2flood)

Figure 1 - Representative Water Analysis Indicating Scaling Tendencies

Table 4 Common Suspended Solids and their Probable Origins

Figure 3 - Calcium Sulfate Scale

Figure 4 - Barium Sulfate Scale

Figure 2 - Calcium Carbonate Scale