Well Stimulation

Well Stimulation

Well stimulation is a specialized intervention performed on oil or gas wells to boost production. By improving the flow of hydrocarbons from the drainage area into the wellbore, stimulation techniques enhance the overall efficiency and output of the well. This process typically involves extending perforation tunnels and creating fractures within the reservoir rock to facilitate better hydrocarbon movement.

Types of Well Stimulation Techniques

There are primarily two types of well stimulation techniques:

1. Acidizing
2. Hydraulic Fracturing (Fracking)

1. Acidizing

Acidizing, also known as acid stimulation, involves using reactive acids to increase the permeability of the reservoir. This method dissolves acid-soluble solids naturally present in the rock matrix or those causing formation damage.

Types of Acidizing

Acidizing can be categorized into two main types:

• Matrix Acidizing
• Fracture Acidizing

Matrix Acidizing:

• Process: Acid is pumped into the formation below the fracture pressure.
• Purpose: Removes acid-soluble damage, enhancing permeability.
• Applications: Suitable for both sandstone and carbonate formations.

Fracture Acidizing:

• Process: Acid is injected above the fracturing pressure of the reservoir rock.
• Purpose: Creates long and open channels to improve hydrocarbon flow.
• Applications: Typically used in carbonate reservoirs with lower permeability compared to sandstone.

Acids Used in Acidizing

• Hydrochloric Acid (HCl)
• Acetic Acid (CH₃COOH)
• Formic Acid (HCOOH)
• Hydrofluoric Acid (HF)
• Mud Acid (HCl-HF)
• Sulfamic Acid (NH₂SO₃H)

Acid Additives:

• Surfactants
• Corrosion inhibitors
• Anti-sludge agents
• Suspending agents

2. Hydraulic Fracturing (Fracking)

Hydraulic fracturing, commonly referred to as fracking or hydrofracturing, is a widely used stimulation method that involves two major steps:

1. Creating Cracks in the Rock Formation: Using a pressurized liquid to fracture the reservoir rock.
2. Proppant Injection: Introducing materials to keep the fractures open, ensuring a continuous flow path for hydrocarbons.

Objective: The primary goal of hydraulic fracturing is to significantly increase well productivity by creating highly conductive pathways for hydrocarbons to flow into the wellbore.

Composition of Fracture Fluid

• Water
• Proppant (e.g., sand)
• Gelling Agents (e.g., guar gum)
• Foaming Agents
• Compressed Gases (e.g., N₂, CO₂, air)
• Corrosion Inhibitors

Stages of Hydraulic Fracturing

1. Spearhead Stage: Mixing water with acid to clear debris and create a pathway.
2. Pad Stage: Injecting fluid before the proppant to break the formation.
3. Proppant Stage: Injecting water and sand, which remains in the formation to keep fractures open.
4. Flush Stage: Pumping fresh water into the wellbore to finalize the process.

Proppants

Proppants are granular materials that prevent the newly created fractures from closing after the fracturing treatment. Common types include:

• Silica Sand
• Resin-Coated Sand
• Bauxite
• Ceramics