Scale 101-Part 2

The ABCs of H2S and mercaptans

Scale in Pipelines 101 – Part 2

In this blog, discover the specific causes of scale in pipelines and the importance of addressing them promptly.

Q2 Technologies Team

Experts in H2S Scavenging Solutions

With decades of combined experience, the Q2 Technologies team specializes in innovative hydrogen sulfide (H2S) scavenging solutions for the oil and gas, wastewater treatment, and industrial sectors.

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Welcome back to our series on pipeline scale. In Part 1, we explored the basics of scale formation and its impact on operations. Now, we’ll delve into the specific causes of scale and the importance of addressing it promptly.

To start, take a look at these pictures showing scale in various parts of the pipeline. These images highlight the real-world challenges posed by scale buildup and underscore the necessity of effective prevention and treatment strategies.

Scale in facility

A sample of these scales was analyzed with XRD, and the results (shown in the graph below) indicate the presence of calcium carbonates and strontium carbonates. The height of the peaks corresponds to the concentrations of these compounds, with higher peaks indicating higher concentrations.

Causes of Scale on operations

This is by no means an exhaustive list, but scale can be caused by the following:

Decreased oil production
Increased water production
Influx of contaminants or formation sand
Plugged tubing strings
Plugged perforations
Stuck or leaking valves
Plugged gas anchors
Blocked flow lines
Fouled fire tubes
Heaters and heat exchangers offline
Cooling tower basins
Damaged boiler tubes
Fouled dump valves
Mismanaged metering equipment
Cemented filters
Downtime for maintenance

…Just to name a few potential headaches!

Removing existing scale:

Regular monitoring and mitigation strategies are essential to prevent scale buildup and maintain the efficiency of oil and gas production operations.

Key reasons for removing scale include:

Production may be adversely affected by a scale layer.
Corrosion is accelerated under a scale layer.
Bacteria grow and thrive under a protective scale layer.
Scale formation accelerates when seated by existing scale. In other words, scale will form quicker in dirty systems than in a clean system. Scale begets scale.

How to Prevent and Treat Scale Formation in Oil Fields?

Always consult a scale or chemical specialist before doing any work that could modify the physical or chemical properties of an asset.

Preventive measures

Careful monitoring and management of the chemical properties of the water.
Various treatments can be used, including chemical inhibitors, mechanical removal, and adjustments to water injection rates and chemistry. The specific approach will depend on the characteristics of the formation water, injection water, and the oil reservoir itself.

Treatment methods

Chemical inhibitors: often used to prevent scale formation by modifying the chemistry of the water to prevent minerals from forming solid deposits.
Mechanical removal: scraping or jetting, to remove scale deposits from equipment.
Adjustments to water injection rates and chemistry may also be made to prevent the mixing of incompatible waters.

Acids for scale treatment

There are two major types of acids used for breaking up scale: mineral acids, which are inorganic, and organic acids, which contain a carbon component.

Mineral Acids:

Hydrochloric acid, most common (HCl)
Hydrochloric + Hydrofluoric acid (Mud acid)
Sulfuric acid (H2SO4)
Nitric acid (HNO3)
Phosphoric acid (H3PO4)

Organic Acids:

Acetic Acid (CH3COOH)
Formic acid (HCOOH)

Challenges:

However, it’s not simply a matter of pumping acid down a well and expecting all scale to dissolve. Proper dissolution requires the acid to effectively contact the scale. Three main challenges are typically encountered: