Standard tools use coaxial antennas (loops parallel to the tool axis). The NGI tool uses a combination of coaxial and tilted antennas. By measuring the phase shift and attenuation of EM waves as they pass through different geological layers, the tool calculates anisotropic resistivity (horizontal and vertical resistivity, Rh and Rv).
Schlumberger’s NGI (Near-Grid Imaging / Networked Geomechanics & Imaging—commonly referred to simply as “NGI”) tool is a specialized technology used in subsurface characterization and wellbore integrity assessment. It combines high-resolution imaging, geomechanical analysis, and data-integration workflows to help operators better understand formation properties, fractures, and wellbore–formation interactions. This post summarizes what the NGI tool does, its primary applications, typical workflow, benefits, and practical tips for field and data teams.
For a complete evaluation, combine NGI with:
| Tool | Purpose | |------|---------| | Density / Neutron | Total porosity, lithology | | Array Induction (e.g., AIT) | Deep ( R_t ) for true ( S_w ) | | Nuclear Magnetic Resonance (NMR) | Clay-bound water, capillary-bound water, permeability | | Elemental Spectroscopy (ECS) | Mineralogy for dielectric mixing law | schlumberger ngi tool
Contrary to popular belief, the NGI tool does not replace full LWD suites; it augments them. In a typical high-end BHA for a shale play, you might see:
In this stack, the NGI provides the local formation data at the bit, while the Periscope looks 15-20 feet around the borehole. The combination gives you "micro" precision (NGI) and "macro" vision (Periscope).
A typical NGI log presentation includes: Standard tools use coaxial antennas (loops parallel to
Track 1: Depth
Track 2: ( \phi_t ) (from density/neutron) overlaid with ( \phi_w ) (from NGI)
Track 3: ( S_xo ) from NGI
Track 4: Resistivity (deep & shallow)
| Feature | Conventional SGR | Schlumberger NGI | |---------|------------------|------------------| | Detector type | NaI (Sodium Iodide) | BGO (Bismuth Germanate) | | Efficiency | Low at high energies | High (3-5x more efficient) | | Logging speed | Slow (20 ft/min) | Fast (up to 60 ft/min) | | Statistical precision | Moderate | Excellent | | Borehole correction | Limited | Advanced (uses 3 detectors) |
The NGI processing chain outputs:
In the high-stakes world of oil and gas exploration, understanding the true geometry of a reservoir is not just an advantage—it is a necessity. Drilling a well is an expensive gamble, and the difference between a commercial discovery and a dry hole often lies in the subtleties of formation evaluation.
For decades, the industry has relied on a suite of logging-while-drilling (LWD) and wireline tools to map the subsurface. Among these, one name stands out when the target is thin-bedded reservoirs, anisotropic formations, or complex structural traps: the Schlumberger NGI tool.
But what exactly is the NGI tool? Why has it become a critical component of modern geosteering and reservoir characterization? This article provides a deep dive into the technology, applications, and operational benefits of the Schlumberger Near-bit Gamma and Inclination (NGI) tool. In this stack, the NGI provides the local