How Far Has Pressure Traveled in Your Reservoir?
In reservoir engineering, pressure tells a story and the radius of investigation helps us read it.
The radius of investigation is the distance from the wellbore to the farthest point in the reservoir that has felt the effects of a pressure disturbance caused by production or injection.
In simpler terms, it’s how far the reservoir “knows” that the well is operating.
🧠 Why Is the Radius of Investigation Important?
This concept is a cornerstone in well testing and reservoir evaluation.
✅ Evaluate Reservoir Properties
It helps assess permeability, porosity, and fluid properties based on pressure behavior.
✅ Define the Drainage Area
Engineers can estimate how much of the reservoir is contributing to the well’s flow.
✅ Detect Boundaries
A sudden pressure change or deviation can signal faults, barriers, or fluid contacts.
📐 How Is It Calculated?
The radius of investigation is calculated using the following formula:
Where:
- ri: Radius of investigation (ft or m)
- : Permeability (mD)
- : Time since the start of the test (hours)
- : Porosity (fraction)
- : Fluid viscosity (cP)
- : Total compressibility (psi⁻¹)
🔍 Interpretation:
Higher permeability or test time → Larger radius- Higher viscosity, porosity, or compressibility → Smaller radius
🎯 Key Factors That Influence It
| Factor | Effect on Radius |
|---|---|
| 🔓 Permeability | High k → Larger radius |
| 💧 Viscosity | High μ → Smaller radius |
| 🧱 Porosity | High φ → Slower pressure propagation |
| ⏳ Test Duration | Longer test → Larger radius |
🔧 Applications in Petroleum Engineering
📊 Reservoir Characterization
Provides insight into reservoir size, heterogeneity, and pressure communication.
🧪 Well Test Interpretation
Helps analyze drawdown, buildup, and interference tests to extract meaningful reservoir parameters.
🗺️ Well Spacing and Drainage
Guides decisions on how far apart to place wells for efficient drainage.
🚧 Boundary Detection
Identifies pressure barriers or faults that affect production.
🔬 Radius of Investigation by Test Type
📉 Drawdown Tests
As the well flows, pressure propagates outward useful for identifying heterogeneities and near-wellbore behavior.
📈 Buildup Tests
After shut-in, pressure data is used to analyze how far the reservoir was “touched” during production.
🔁 Interference Tests
Assesses connectivity between wells by monitoring the pressure response in an observation well.
⚠️ Challenges and Limitations
| Challenge | Description |
|---|---|
| 🧪 Uncertain Reservoir Properties | Errors in k, φ, μ, or cₜ can mislead interpretation |
| 🗻 Complex Geology | Faults and layers disrupt uniform pressure propagation |
| ⏱ Short Test Duration | May not reach boundaries, limiting data value |
✅ Conclusion: The Value of Radius of Investigation
The radius of investigation isn’t just a distance it’s a diagnostic window into your reservoir’s behavior.
Understanding how far pressure travels gives engineers the power to:
- Optimize well spacing
- Fine-tune production strategies
- Detect and map reservoir boundaries
- Design smarter reservoir management plans
🎓 Want to Go Deeper?
At Petrosmart, we empower petroleum professionals with practical knowledge.
📚 Join our Telegram Channel for:
- Exclusive ebooks on well testing
- Step-by-step guides on pressure analysis
- Advanced resources on radius of investigation and beyond
💬 Join the Conversation
How do you use the radius of investigation in your work?
- Have you used it to identify boundaries?
- What challenges have you faced during pressure test interpretation?
👇 Share your experiences in the comments we’d love to hear your insights!
0 Comments