How Oil or Gas is Discovered
- Surface Geology Studies
- Geologists look for rock formations (anticlines, salt domes, fault traps) that can act as reservoirs.
- Outcrops, seeps (oil/gas at surface), and rock sampling give first clues.
- Geophysical Surveys
- Seismic Surveys (2D, 3D, now even 4D time-lapse):
- Sound waves are sent into the ground. Reflections from different layers show subsurface structure.
- Software models the reservoir geometry.
- Gravity & Magnetic Surveys:
- Detect density or magnetic variations → hints at possible hydrocarbon-bearing basins.
- Seismic Surveys (2D, 3D, now even 4D time-lapse):
- Geochemical Surveys
- Soil, water, or gas samples are tested for hydrocarbon “microseepage.”
- Biomarkers can indicate presence of petroleum systems.
- Exploration Wells (Wildcat Drilling)
- After surveys, a test well (exploration well) is drilled.
- Mud logging: gases in drilling mud analyzed for hydrocarbons.
- Core samples: rock is cut and analyzed for porosity & permeability.
- Well Logging (Wireline Logs) – Data Gathering Downhole
- Tools lowered into the well measure rock & fluid properties:
- Resistivity Log → Hydrocarbon zones show high resistivity (water conducts electricity, oil/gas doesn’t).
- Gamma Ray Log → Identifies shale vs. clean sandstone.
- Neutron & Density Logs → Show porosity & fluid type.
- Sonic Log → Measures acoustic velocity, relates to porosity.
- Combining logs gives a picture of reservoir quality.
- Tools lowered into the well measure rock & fluid properties:
- Drill Stem Test (DST) / Well Testing
- Well is temporarily completed to allow fluids (oil, gas, water) to flow.
- Pressure & flow measurements indicate reservoir capacity & fluid type.
- Reservoir Engineering & Simulation
- Data from cores, logs, and tests used to build 3D reservoir models.
- Simulation estimates reserves, flow rates, and economic viability.
What Data is Gathered During Oil/Gas Discovery
| Stage | Data Collected | Purpose |
| Surface Survey | Rock samples, outcrop data, structural maps | Identify possible traps |
| Seismic Survey | Reflection times, amplitudes, velocity models | Map subsurface layers, detect traps |
| Geochemical Survey | Soil gas, biomarkers, isotopes | Detect hydrocarbon seepage |
| Drilling (Mud Logging) | Cuttings, gas readings, mud returns | Real-time hydrocarbon detection |
| Core Sampling | Rock porosity, permeability, saturation | Reservoir quality |
| Wireline Logging | Resistivity, gamma ray, density, neutron, sonic logs | Fluid identification & formation evaluation |
| Well Testing (DST) | Flow rate, pressure buildup/drawdown, fluid samples | Reservoir deliverability & fluid type |
| Production Testing | Oil/gas/water cut, GOR (Gas-Oil Ratio), PVT analysis | Commerciality check |
Summary
- Oil and gas are discovered by combining surface geology, geophysical surveys, geochemical data, drilling logs, core analysis, and well testing.
- The key basis for discovery is whether the reservoir has enough hydrocarbons, is porous/permeable enough, and is sealed properly to trap oil/gas.
- Data is gathered at every stage — from seismic images to actual downhole logs and production tests.
🔎 Sensors Used to Access Oil/Gas
- Seismic & Survey Sensors
- Geophones / Hydrophones – detect seismic wave reflections on land and offshore.
- Vibrators (land) / Air guns (offshore) – source of seismic energy.
- Gravity meters, Magnetometers – measure variations in Earth’s gravity and magnetic field to detect basin structures.
- Drilling Stage Sensors
- Mud Logging Sensors
- Gas detectors → measure hydrocarbons in drilling mud.
- Chromatographs → separate hydrocarbon gases (C1–C5).
- Cutting analyzers → check rock type while drilling.
- Measurement While Drilling (MWD) / Logging While Drilling (LWD)
- Downhole sensors measure resistivity, density, porosity, gamma ray, and acoustic data in real time.
- Gyroscopes & accelerometers → provide well trajectory.
- Pressure & temperature sensors → monitor wellbore safety.
- Wireline Logging Sensors (after drilling)
- Gamma Ray Detectors → distinguish shale vs. clean sand.
- Resistivity Tools (induction, laterolog) → detect oil/gas vs. water zones.
- Neutron & Density Sensors → measure porosity & fluid type.
- Sonic/Acoustic Sensors → measure sound velocity to infer porosity and mechanical properties.
- NMR (Nuclear Magnetic Resonance) Logging → fluid typing and permeability estimate.
- Well Testing & Production Sensors
- Downhole pressure & temperature gauges → measure reservoir behavior.
- Multiphase flow meters → measure oil, gas, water fractions.
- Coriolis & Turbine flow meters → measure produced fluid flow rates.
- PVT (Pressure-Volume-Temperature) analyzers → for gas-oil ratio, fluid properties.
- Fiber Optic Sensors (DTS/DAS) → distributed temperature/strain sensing along wellbore.
Software Used in Oil/Gas Exploration & Access
- Seismic Interpretation & Reservoir Modeling
- Schlumberger Petrel – seismic-to-simulation platform for reservoir modeling.
- Halliburton Landmark (DecisionSpace) – seismic interpretation & well planning.
- Paradigm (Emerson) – seismic processing & reservoir characterization.
- Kingdom Suite (IHS) – seismic and geological interpretation.
- Drilling & Well Planning Software
- Landmark WellPlan / Compass – well trajectory design.
- Schlumberger Techlog – well logging data interpretation.
- Baker Hughes JewelSuite – drilling optimization.
- Rig instrumentation software – real-time drilling monitoring (WITSML protocol).
- Reservoir Engineering & Simulation
- Eclipse (Schlumberger) – reservoir simulation.
- CMG (Computer Modelling Group) – thermal, compositional, unconventional reservoir modeling.
- tNavigator – dynamic simulation & flow modeling.
- Production Monitoring & Optimization
- PI System (OSIsoft, now AVEVA) – real-time production data historian.
- WellView – wellbore schematics & reporting.
- KAPPA Workstation – production analysis (pressure transient, decline curve).
- SCADA/DCS systems – field automation & remote monitoring.
- AI/ML & Data Analytics (Modern Tools)
- C3.ai, Palantir Foundry, Azure Energy AI – predictive analytics, drilling optimization.
- Custom ML algorithms – seismic fault detection, reservoir property prediction.
- Digital Twins – simulate well & reservoir behavior virtually.
Summary
Sensors: Seismic geophones, mud logging gas detectors, LWD/MWD downhole tools, wireline sensors (gamma, resistivity, neutron, NMR), flow meters, fiber optics.
Software: Petrel, Landmark, Techlog, Eclipse, CMG, PI System, SCADA, plus AI/ML tools for prediction and automation.
Together, these allow oil companies to find, evaluate, and optimize hydrocarbon production safely and efficiently.