Damage during drilling

1-Tubing Damage
2-Matrix Damage
3-Deposition within Porous Formation
Reason for Scale Control: Tubing Damage
•Tubing ID Restriction
1-Constrained production
2-Often layered with scale, wax, asphaltene, etc.
•Completion components blocked with scale
1-Gas Lift Mandrels
2-SSSV
3-Nipples, ..etc
•Corrosion under scale deposition
1-Bacterial / H2S
2-Pitting
3-Loss of steel integrity
Reason for Scale Control: Matrix Damage
1-Hydrocarbon flow through water-saturated matrix
2-Scale deposition restricts flow
3-Scale reduces matrix permeability
4-Complete scaling of pore throat not likely; however,
5-Small quantity of scale =large loss in permeability
6-Large loss in permeability =significant reduction in productivity
Organic Deposit
A type of damage in which heavy hydrocarbons precipitate when temperature or pressure is reduced.
1-These deposits are commonly located in the tubing,gravel pack and perforations, or inside the formation . The injection of cold treating fluids promotes the formation of organic deposits.
2-Organic deposits such as paraffins or asphaltenes are resolubilized using aromatic organic solvents such as toluene or xylene.
3-Small amounts of alcohol help to further dissolve asphaltenes.
Organic deposits are heavy hydrocarbons (paraffins or asphaltenes) that precipitate as the pressure or temperature is reduced.
They are typically located in the tubing, perforations or formation.
1. Paraffins: (dissolved in oil)
Paraffins are the simplest of hydrocarbons. They are composed of only carbon and hydrogen atoms, and the carbons occur as an unbranded chain.
2. Asphaltenes: (undissolved, but suspended as a colloid in oil)
Asphaltenes are organic materials consisting of condensed aromatic and naphthenic ring compounds with molecular weights of several hundred to several thousand. In “solution,” they usually exist as a colloidal suspension,
3. Tar:
-Tar is simply an asphaltene or other heavy-oil deposit. It cannot be removed by acid or mutual solvents. Removal requires dispersion in an aromatic solvent, and energy is typically necessary to achieve removal.
4. Resins :
-(Peptizing agent, dissolved in oil, help suspend asphaltene in oil)
5. Wax:
-A combined deposit of paraffins, asphaltenes, resins, mixed with clays, sand, and debris (dissolved in oil)

Scale Inhibitor

A chemical treatment used to control or prevent scale deposition in the production conduit or completion system.
Scale-inhibit or chemicals may be continuously injected through a down hole injection point in the completion, or periodic squeeze treatments may be undertaken to place the inhibitor in the reservoir matrix for subsequent commingling with produced fluids.Some scale-inhibitor systems integrate scale inhibitors and fracture treatments into one step, which guarantees that the entire well is treated with scale inhibitor. In this type of treatment, a high-efficiency scale inhibitor is pumped into the matrix surrounding the fracture face during leak off.
It adsorbs to the matrix during pumping until the fracture begins to produce water. As water passes through the inhibitor-adsorbed zone, it dissolves sufficient inhibitor to prevent scale deposition. The inhibitor is better placed than in a convention a scale-inhibitor squeeze, which reduces the re-treatment cost and improves production.

Inhibitor Types

There are a number of scale inhibitor types:
1.Inorganic phosphates.
2.Organo phosphorous compounds.
3.Polyvinyl sulphonate co-polymers.
4.Organic polymers.
5.Blends of phosphonates and polymers.

Scale inhibitors prevent undesirable buildup on your equipment. Appropriate treatment by NCP Scale Inhibitors will extend the life of industrial equipment and provide optimal process conditions.Fields where NCP Scale Inhibitors can be used are:Oil and Gas field
1-Water injection
2-Refineries
3-Water desalination
4-Power plants
5-Industrial waters

Mineral Scale

Mineral scales (subsequently referred to as scales) are inorganic solids precipitated from water and subsequently deposited. Scales are a common form of formation damage and blockages or restrictions to perforations, screens, liner or tubing.
Like most production chemistry problems, they pose a safety issue through loss of operability of check valves, safety valves or, in severe cases, tree valves. To predict the scaling potential of reservoir aquifer water, a representative water sample is required.
This requires that an appraisal or exploration well deliberately produces water, and that any contaminants such as completion or drilling fluids are also analyzed so that interference is backed out.
The water chemistry of hydrocarbon bearing reservoirs is highly variable, ranging from very low ion strength to high salinity brines containing a wide range of various ions.
Prevention and mitigation:
1.Mitigate or prevent scale in formation by using formation water instead of seawater,
2.Scale Inhibitor
Scales:
Hard inorganic crystals (~ 3 –4 mhos)
1-Slightly less than steel (5 mhos)
2-Diamond, 9 mhos
3-Variable crystal size
4-Microns to centimeters
5-Produced form aqueous solutions
6-Soluble in specially formulated solutions

Scale Types

The equilibrium that existed for so long is then upset on a geologically diminutive timescale during the production phase of the field development.
Production creates pressure and temperature reduction or introduces new fluids (muds, completion fluids or water injection).
The main types of scales are:
1-Carbonates–mainly calcium carbonate, but also iron carbonate
2-Sulphates–barium, strontium and calcium
3-Sulphide–less frequently encountered scales, but include lead, zinc and iron
4-Salts–mainly sodium chloride;
Most Common Types of Scales
1-Calcite (CaCO3)
–Formed due to the presence of calcium ions and bicarbonate ions in the produced water
–Pressure changes may cause precipitation

2-Barite (BaSO4)
–Generally formed when there is co-production of formation water (Ba2+) and injection water (SO4-)

Hydrogen Sulfide Gas Problems

Hydrogen sulfide is a colour less, flammable, poisonous gas that smells like rotten eggs.
Hydrogen Sulfide gas is very dangerous and in high concentrations is lethal and in low concentration gives a rotten eggs mell.
Hydrogen sulfide(or hydrogen sulphide) is the chemical compound with theformulaH2S. This colorless, toxic, flammable gas is partially responsible for the foul odor of rotten eggs and flatulence. It often results from the bacterial break down of sulfur-containing organic matter in the absence of oxygen, such as in swamp sand sewers (anaerobic digestion). It also occurs in volcanic gases,natural gas and some well waters. The body produces small amounts of H2S and uses it as a signaling molecule.

Safety

Hydrogen sulfide is a highly toxic and flammable gas. Being heavier than air, it tends to accumulate at the bottom of poorly ventilated spaces. Although very pungent at first, it quickly deadens the sense of smell, so potential victims may be unaware of its presence until it is too late. For safe handling procedures, a hydrogen sulfide material safety data sheet (MSDS)should be consulted.

Toxicity of H2S

Hydrogen sulfide is considered a broad-spectrum poison, meaning that it can poison several different systems in the body, although the nervous system is most affected. The toxicity of H2S is comparable with that of hydrogen cyanide. It forms a complex bond with iron in the mitochondrialcy to chromeenzymes, thereby blocking oxygen from binding and stop ping cellular respiration. Since hydrogen sulfide occurs naturally in the environment and the gut, enzymes exist in the body capable of detoxifying it by oxidation to (harmless) sulfate.Hence, low levels of sulfide may be tolerated indefinitely.
At some threshold level, believed to average around 300–350 ppm, the oxidative enzymes become overwhelmed. Many personal safety gas detectors, such as those used by utility, sewage and petrochemical workers, are set to alarm at as low as 5 to 10 ppm and to go into high alarm at 15 ppm.
Exposure to lower concentrations can result in eye irritation, a sore throat and cough, nausea, shortness of breath, and fluid in the lungs. These symptoms usually go away in a few weeks. Long-term, low-level exposure may result in fatigue, loss of appetite,headaches, irritability, poor memory, and dizziness. Chronic exposures to low level H2S (around 2ppm) has been implicated in increased miscarriage and reproductive health issues amongst Russian and Finnish wood pulp workers, but the reports have not (as of circa 1995) been replicated.

Toxicity of H2S in Details

0.0047ppmis the recognition threshold, the concentration at which 50% of humans can detect the characteristic odor of hydrogen sulfide, normally described as resembling "a rotten egg".
Less than 10 ppm has an exposure limit of 8 hours per day.
10–20 ppm is the borderline concentration for eye irritation.
50–100 ppm leads to eye damage.
At 150–250 ppm the olfactory nerve is paralyzed after a few inhalations, and the sense of smell disappears, often together with awareness of danger,
320–530 ppm leads to pulmonary edema with the possibility of death.
530–1000 ppm causes strong stimulation of the central nervous system and rapid breathing, leading to loss of breathing;
800 ppm is the lethal concentration for 50% of humans for 5 minutes exposure(LC50).
Concentrations over 1000 ppm cause immediate collapse with loss of breathing, even after inhalation of a single breath.
Hydrogen sulfide was used by the British as a chemical agent during World War One. It was not considered to be an ideal war gas, but while other gases were in short supply it was used on two occasions in 1916.The gas, produced by mixing certain household ingredients, was used in a suicide wave in 2008, primarily in Japan.