Full Workflow and Main Technologies of Well Logging

In modern oil and gas exploration and development, "logging" has evolved far beyond the traditional suite of Gamma Ray and resistivity curves. It has transformed into a comprehensive, multi-physics field system integrating borehole, formation, fluid, and mechanical data, often acquired in real-time during drilling.

Modern logging is not a single measurement but an integrated evaluation system composed of:

(I) The 10 Key Technology Families

(II) The 4 Operational Platforms (How Logging is Executed)

These technologies are deployed via four primary platforms, which work in concert across the well's lifecycle:

• Wireline Logging: The classic method, run after drilling is complete. It provides the highest density and highest resolution data (e.g., imaging, NMR) for detailed reservoir evaluation.
• Logging While Drilling (LWD): Measurements are taken during the drilling process and transmitted in real-time. This platform is essential for geosteering and acquiring data before deep mud invasion.
• Cased-Hole Logging: Operations performed after casing is set. Used for evaluating cement jobs (CBL), monitoring reservoir depletion and fluid contacts (PNN, C/O), and production logging (PLT).
• Digital Logging: An overarching platform that integrates multi-source data (logs, core, production) and applies AI and machine learning models for automated interpretation, pattern recognition, and reservoir characterization.

Modern logging systems are designed to provide six interconnected capabilities, moving from basic rock characterization to dynamic fluid and mechanical properties.

1. Formation Identification (GR / Spectral GR)
Beyond simple clay content, spectral gamma ray (K, U, Th) provides insights into depositional environment, mineralogy, and even organic richness in shales. It's a "formation fingerprint."

2. Reservoir Electrical Properties (Resistivity)
A suite of resistivity measurements (deep, shallow, micro) defines fluid saturation (using Archie's equation) and invasion profiles. High-resolution electrical imaging (FMI) reveals bedding, fractures, and sedimentary features at the borehole wall.

3. Porosity & Pore Structure (Density / Neutron / Sonic / NMR)
The classic "porosity trio" (density, neutron, sonic) remains fundamental. However, NMR logging represents a major advancement, providing the T₂ spectrum which distinguishes between clay-bound water, capillary-bound water, and movable fluids, and yields a continuous permeability estimate.

4. Geological Structure & Fracture Identification (Imaging)
Borehole imaging (electrical and acoustic) is revolutionary, providing a high-resolution "picture" of the borehole wall. It allows direct interpretation of fractures (natural and induced), stress directions, fault zones, and fine-scale sedimentary features, critical for both conventional and unconventional reservoirs.

5. Formation Mechanics (Advanced Sonic)
This capability is vital for the unconventional era. Advanced sonic tools (like SonicScanner) measure compressional (Vp) and shear (Vs) wave velocities in multiple directions. This data yields dynamic elastic properties (Young's modulus, Poisson's ratio), rock strength, anisotropy, and stress orientation, which are essential inputs for geomechanical modeling and hydraulic fracture design.

6. Fluid & Production Logging (Formation Testers / Cased-Hole)
Formation testers (MDT) provide definitive answers: direct pressure measurements, fluid gradients to define contacts, and fluid samples. Downhole Fluid Analysis (DFA) characterizes fluids in-situ (GOR, composition). Cased-hole tools like PNN, C/O, and PLT monitor fluid saturations behind casing and well production profiles over time.

These capabilities and platforms are deployed in a coordinated sequence across a well's lifecycle.

Phase 1: Drilling (LWD for Geosteering): Real-time LWD data (GR, resistivity, density-neutron, and deep-directional resistivity) guides the wellbore to stay within the optimal reservoir zone.

Phase 2: Post-Drilling (Wireline for Evaluation): Once total depth is reached, a wireline program is run. This includes a basic suite (GR, resistivity, porosity) for standard calculations, followed by advanced logs (imaging, NMR, sonic, formation tester) for detailed reservoir characterization, fracture analysis, and fluid typing.

Phase 3: Production (Cased-Hole for Monitoring): During the production phase, cased-hole logs are run to evaluate cement integrity (CBL), monitor saturation changes (PNN, C/O) to identify bypassed oil or water encroachment, and run production logs (PLT) to determine zonal contributions.

Phase 4: Full Integration (Digital Logging): All acquired data (wireline, LWD, core, production) is integrated. AI and machine learning are increasingly used for automated multi-well correlation, electrofacies classification, and building predictive reservoir models.

Modern logging has evolved from simple curve interpretation into a complete formation-fluid-mechanics evaluation system. It integrates data from multiple physical principles across wireline, LWD, and cased-hole platforms. This holistic system supports every stage of field development, from exploration and geosteering to detailed reservoir characterization, hydraulic fracturing design, and production optimization, including applications in unconventional resources and CO₂ storage. Understanding this modern framework is now essential for any engineer involved in subsurface evaluation. For more detailed information, please don't hesitate to contact Vigor team for more detailed product information.