04.01- Geosteering Introduction

What Is Geosteering?

Geosteering is the practice of adjusting a wellbore trajectory in real time based on geological data rather than just the planned survey. While directional drilling focuses on getting the bit to a specific coordinate, geosteering ensures the bit stays within the most productive part of the reservoir.

Geosteering bridges the gap between petrophysics and drilling engineering. A geosteering engineer monitors the influx of data to understand the subsurface environment, ensuring the well maximizes reservoir contact and avoids non-productive zones.

The Geosteering Workflow

Geosteering is a continuous, iterative cycle. It requires integrating data from three primary sources:

1. Planning: Before drilling, the team builds a geological model based on seismic surveys and offset wells. This creates a “target window.”
2. Monitoring: As the drill bit advances, MWD data (gamma ray, inclination) and LWD data (resistivity, porosity) arrive at the surface in real time.
3. Steering: The engineer compares the live data to the model. If the data suggests the bit is exiting the target formation (e.g., the gamma ray reading changes unexpectedly), the engineer communicates with the directional driller to adjust the path.

Key Geosteering Objectives

• Maximize Reservoir Exposure: Keeping the wellbore in the “pay zone” for as long as possible to increase production.
• Avoid Hazards: Steering away from faults, water-bearing zones, or geologically unstable formations.
• Optimize Efficiency: Reducing unnecessary “doglegs” or sharp curves that increase torque and drag, which can hinder long horizontal sections.

Geosteering vs. Directional Drilling

It is important to distinguish between these two roles:

• Directional Drilling is the “How.” It involves the tools, the motors, and the mechanical skill required to physically move the bit.
• Geosteering is the “Where.” It involves the geological interpretation and the decision-making process that directs the directional driller on where to go.

What You Will Learn in This Lesson

This lesson serves as the gateway to the core of your training. You will learn:

1. How to create a geological “type log” for correlation.
2. How to identify “picks” (markers) in the formation to track your position.
3. How to interpret dip and stratigraphic thickness.
4. How to document and report steering decisions effectively.
5. Best practices for communication between the office and the rig site.

→Next Lesson: [05 – True Stratigraphic Position TSP]