Advanced Geosteering Equations: Part 2
Mastering advanced geosteering equations is vital for high-precision well placement. While Part 1 covered the basics of dip and inclination, this lesson explores how to handle complex geometry, including fault crossings and changing bed thicknesses.
Calculating Vertical Bed Thickness
Often, the formation is not perfectly horizontal. To understand the true reservoir potential, you must calculate the Vertical Bed Thickness (VBT).
If you know the True Stratigraphic Thickness (TST) (the thickness measured perpendicular to the rock layers), you can derive the VBT using the formation dip angle:
- VBT = TST / cos(dip)
Consequently, as the formation dip increases, the vertical thickness of the bed appears to increase on your logs. Recognizing this is crucial to avoid misinterpreting a steep dip as a thickening reservoir.
Handling Fault Crossings
Furthermore, faults introduce discontinuities that break your geometric model. When you cross a fault, your depth marker “jumps.”
- Normal Faults: These cause a “missing section” in your logs. You appear to jump from a younger rock layer to an older one.
- Reverse Faults: These cause a “repeated section.” You see the same rock sequence twice.
Therefore, by analyzing the jump in your logs, you can mathematically estimate the “throw” (the vertical displacement) of the fault. You can learn more about these structural dynamics at the American Association of Petroleum Geologists (AAPG).
Summary of Advanced Analysis
- VBT Correction: Always adjust for dip when estimating the size of your target zone.
- Fault Recognition: Use log jumps to identify and map structural breaks.
- Proactive Modeling: Integrate these calculations into your software to update the reservoir model in real-time.
In conclusion, these advanced geosteering equations provide the framework for professional well placement. By mastering these principles, you ensure your well stays in the most productive zones, even in highly faulted or complex geological settings.