The performance of an oil or gas well depends on how easily fluids can flow from the reservoir to the wellbore. Several factors influence this process, including the permeability of the reservoir rock, the thickness of the producing formation, the pressure difference between the reservoir and the well, the properties of the fluids, and the geometry of the wellbore itself. Altered conditions near the wellbore can also strongly affect production. Mud invasion during drilling can often damage the permeability near the wellbore, while stimulation treatments such as acid jobs can enhance near wellbore permeability. Hydraulic fracturing is categorized as a stimulation method, but it is not limited to changing near wellbore conditions. Because of that distinction, that hydraulic fractures can reach thousands of feet away from the wellbore, we consider their stimulation effect to be an alteration of wellbore geometry.
Why It Matters
Many hydrocarbon reservoirs, especially unconventional formations such as shale and tight sandstones, have extremely low permeability. In these formations, natural flow toward the wellbore is often insufficient to produce hydrocarbons at economic rates. Hydraulic fracturing is used to overcome this limitation by creating fractures that extend into the reservoir, providing efficient pathways for fluid flow. Understanding what controls well performance helps engineers design fractures that maximize production and improve reservoir recovery.
Learning Objectives
- Explain the steady-state inflow equation and identify the parameters that control production rate.
- Describe how near-wellbore conditions affect well performance using the skin factor.
- Explain why low permeability reservoirs often require hydraulic fracturing.
- Define dimensionless fracture conductivity and describe its role in evaluating fracture effectiveness.
- Identify the key fracture properties that control production improvement, including fracture half-length and fracture conductivity.
