FAQ - Oilfield Technology

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FAQ – Oilfield Technology

Oilfield Technology

The main technical questions

Read the most frequently asked technical questions about the Oilfield Technology market.

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CORROSION INHIBITORS

1 – What are corrosion inhibitors?

Corrosion inhibitors are organic or inorganic compounds capable of reducing or eliminating corrosion caused in environments with corrosive agents.

2 – What are the properties and mechanisms of corrosion inhibitors?

The oil industry uses film forming amines with adsorption characteristics, or which form a protective film against the action of corrosion-causing compounds on metal surfaces.

3 - What causes corrosion in oilfield systems?

Corrosion is caused by factors such as temperature, high levels of salinity of the environment, the presence of carbon dioxide (CO₂), hydrogen sulfide (H₂S), and runoff conditions.

4 - What performance tests are done for corrosion inhibitors?

The following tests are commonly used for performance evaluation of corrosion inhibitors:

Bubble Test
Rotating cylinder electrode (RCE) test
Rotating Cage Test
Flow loop test

5 – What is the importance of the kinetics of corrosion inhibitors in performance tests?

The kinetics of a corrosion inhibitor are related to the speed of formation of a protective film around the metal. With this film, there is a decrease in the electrochemical reactions between the metal and the environment and, consequently, a decrease in the rate of corrosion.

NON-EMULSIFIER

1 - What is a non-emulsifier?

Non-emulsifiers are products that prevent the formation and stablize emulsion.

2 - Where are non-emulsifiers used?

They are used in oil wells in the well stimulation stage.

3 - What is the difference between a non-emulsifier and a demulsifier?

They are products with different purposes. Non-emulsifiers are applied to prevent emulsion prior to stabilization. De-emulsifiers, on the other hand, are used when there is a stable emulsion and it is necessary to break this stability by separating the water from the oil.

4 - Why are non-emulsifiers needed in acidification stimulation?

Acid stimulations promote the formation of stable emulsions, so emulsion preventors must be added.

5 - How are non-emulsifiers tested?

Tests are carried out with crude oil, completion/stimulation fluids, and emulsion preventers to evaluate emulsion breakage at pre-defined times.

FLOWBACK

1 - What is flowback?

Flowback is the return of fluid injected into the rock during the oil reservoir stimulation operation due to the thrust caused by the internal pressure of the rock. Flowback additives reduce the damage caused to the formation, contribute to the return of injected fluids, and facilitate the separation between them and the oil produced.

2 – Surfactants: what is surface tension and interfacial tension?

Interfacial tension is the work required to increase the interface size between two immiscible fluids. If the interface is air/liquid, the term surface tension can be used. Although cohesive forces are relevant, the main forces involved in interfacial (or superficial) tension are the adhesive forces (tension) between the fluids. So, surfactants, which are at the water/oil interface (or on the surface of the water), reduce the interfacial (or superficial) tension.

3 - What is hydraulic fracturing?

Hydraulic fracturing is a technique to stimulate oil and gas reservoirs suitable for rocks with low permeability. Hydraulic fracturing involves injecting water, sand, and chemicals under high pressure into a rock formation through the well. This process aims to increase the permeability of the reservoir by creating new fractures in the rock, increasing the size, extent, and connectivity of existing fractures.

4 – How important is flowback in hydraulic fracturing?

The return of fluids injected into the reservoir to the surface (flowback) is necessary to reduce the damage caused to the formation after the stimulation operations of the oil reservoirs. The use of flowback additives contributes to improving the cleaning of reservoirs, maintaining the wettability characteristics of rocks, and preventing the formation of stable emulsions with injected fluids and the oil produced.

5 - What is the relationship between surfactants and flowback?

Surfactants are molecules that have two different groups of solubility tendencies, a water-soluble polar group commonly called the head, and an oil-soluble hydrocarbon, called the tail. The surfactant used as a flowback additive reduces the surface tension of the fluids used in reservoir stimulation operations and the interfacial tension between these fluids and oil. This causes the stimulation fluids not to accumulate in the pores of the rocks and so they return to the surface. Oil flows through the reservoir channels more easily, and stable emulsions are not formed with stimulation fluids and petroleum.

DEMULSIFIER

1 - What is a demulsifier?

Demulsifiers are surfactants that act on the breaking of the stable emulsion – between the aqueous and oily phases.

2 - What is an emulsion?

Emulsion is the combination of two liquids that are initially incompatible, but in the presence of stabilizing agents, such as solid particles, it manages to form a stable emulsion.

3 - What is the relative solubility number (RSN)?

The relative solubility number is a practical alternative to HLB and is used to check the hydrophobic characteristics of each product.

4 - What is the test method for determining the relative solubility number (RSN)?

The RSN is determined by titration of the sample using Dioxan or toluene.

5 - What types of demulsifiers are there?

Demulsifiers can be classified into chemical groups, or functionality. In the former, there are alcoxylated resins, block copolymers, alkoxylated polyols, polyethyleneimine, polyglycols, etc. In the latter, the applications in oil are Treaters, Droppers, Dryers, and Cleaners.

LUBRICANT

1 - What is a lubricant?

It is the product responsible for reducing friction, wear and/or heating of surfaces that are in contact with movement.

2 - What is the coefficient of friction, torque, and drag?

Friction is a mechanical force of resistance to a movement (sliding or rolling) between two surfaces. When we talk about drilling and completing fluids, we have rotational movements and descent and ascent movements of columns and equipment. The friction generated by the rotational motion of the drill column is known as torque. The resistance force resulting from the ascent and descent of drill columns or other equipment is known as drag force.

3 - What are the main performance tests for lubricants?

The main test for lubricant is the lubricity test, done in equipment developed for evaluations of drilling and completement fluids, called a Lubricity Tester. It simulates a condition of the drilling process, where we have friction between two metal surfaces, in the fluid to be evaluated (drilling or completion). It is important to note that in addition to the lubricity assessment, all evaluations for aqueous fluids (described in API 13B-1) should be performed for any drilling and supplementation fluid additive.

4 - How are lubricants used in completion brines?

In Completion, the torque challenge is not as problematic as in drilling, but nevertheless a lubricant is essential for optimizing the descent of equipment, especially in the completion of horizontal or very extensive zones. The choice of this lubricant should also be made carefully, as it will contact the production zone directly and must not damage it.

5 - What differentiates a drilling lubricant for completion?

All fluid additives have a specific purpose, which matches the operation and the type of formation to be drilled. When we talk about drilling and completion, we have different operational scenarios. For example, drilling requires more than one lubricant in terms of performance, because the friction in the drilling process is much higher, especially in high-extension or directional wells. On the other hand, the lubricants used in completion brines need to undergo an evaluation: turbidity, because this type of lubricant must be soluble in the saline solution and not lose performance amid the high concentration of ions in the fluid.

CASING CLEANER

1 - What is a casing cleaner?

A degreaser surfactant that helps in cleaning the well by changing synthetic base fluid to aqueous base.

2 – How important is it to apply a casing cleaner?

The product eliminates oily deposits on the metal downhole surface. Without cleaning, emulsions may form in the aqueous base brine, which makes it difficult to pump.

3 - Which drilling stage are casing cleaners introduced in?

In well completion stage when the flushing liquid is used.

4 - What tests are performed for casing cleaners?

Gravimetric evaluation of oil removal in a rotor with a metallic surface.

5 - What are the required toxicity limits?

There are no specific restrictions for this application, as the fluid is injected into the well in a flow that returns to the surface.

VISCOELASTIC

1 - What does viscoelastic mean?

Viscoelastic materials combine two different properties. The term viscous implies that they deform when exposed to an external force. The term elastic implies that once the external force has been removed, the material will return to its original configuration. The materials that combine these two characteristics show unique features, such as excellent absorption and enhanced rigidity with the increase of the force applied to the material. Viscoelastic fluids used in operations carried out in oil and gas wells improve productivity and reduce the complexity and number of chemical additives used.

2 - What is rheology?

Rheology is the study of how materials flow or deform when a force is applied. If the force is applied in a purely viscous liquid, it deforms proportionally to the measure of the applied force. An ideal solid deforms elastically – that is, when the energy required for deformation is removed, the body returns to its original form. Rheology describes the behavior of real materials, which exhibit a combination of elastic and viscous behaviors. In addition, it establishes relationships between the mechanical behavior of the material and its micro or nanometric structure.

3 – How important is the application of viscoelastic?

The viscoelastic properties of a fluid can be optimized to meet specific needs. There are several applications for viscoelastic materials in the pharmaceutical and cosmetic industry, food industry, chemical and fine chemical industry, construction industry, agrochemical industry and oil and gas industry. Viscoelastic fluids used in operations carried out in oil and gas wells improve productivity and reduce the complexity and number of chemical additives used.

4 - What are the properties and mechanisms of action of a viscoelastic fluid?

Viscoelastic fluids have the characteristics of viscous fluids and elastic solids. When a force is applied to a viscoelastic material, it stores energy in elastic form and partially returns to its original state, but part of the energy is also dissipated by viscous deformation. The viscoelastic fluid used in the stimulation operations of oil and gas reservoirs is designed to easily drain through rock channels, transport solid materials (known as proppants) and return to the surface when the pressure applied to the reservoir is relieved.

5 - What temperature range does a viscoelastic fluid work in?

Viscoelastic fluids are developed to be efficient in the operating temperature range. A viscoelastic fluid developed for stimulation operations of oil and gas reservoirs, for example, will be efficient in the temperature range of the reservoirs.

SOLVENT

1 – What is a solvent?

It’s a substance that allows other substances—known as solutes—to dissolve in it, thus forming a solution.

2- Where and why do we use solvents in the oil&gas industry?

The solvent is used as a base in different applications for the oil and gas sector, such as demulsifiers, asphaltene inhibitors, H₂S scavengers, etc. It’s important to facilitate the application of the product by adjusting parameters such as viscosity and aspect, and it has economic importance, since not every product needs to apply in concentrated form.

It’s important to highlight that the Brazilian main operator is currently looking for products with non-flammable characteristics for its operations, and solvents contribute significantly to this objective.

3 – What are flammable solvents?

Substances that meet the following characteristics:

Substances that, in contact with air and even at room temperature, can heat up and end up catching fire, even without an active heating source;
Substances that, in contact with water or air humidity, can produce highly flammable gases
Substances that have a flash point between 21ºC and 60ºC (70 ºF and 140 ºF)

4 – What is a flash point?

The lowest temperature at which a compound vaporizes sufficiently to form a flammable mixture with oxygen in the air.

5 – How to measure flash point?

The flash point can be measured by heating substances inside an open or closed cup, in certain temperature ranges, if when we add an ignition source inside the container and a spark occurs, this is the flash point of the substance.

THE MAIN TECHNICAL QUESTIONS