I. Core Responsibilities — Geologist (Tight Oil & Gas Reservoirs)
Focuses on subsurface characterization, well placement, and frac-ready geologic models tailored to nano-Darcy systems with strong stress and capillary controls.
- I.1 — Play and sweet-spot definition: integrate cores, logs, seismic, and production to map TOC, brittleness, natural fractures, pressure, and fluid phase windows.
- I.2 — Stratigraphic framework: build sequence/facies models, correlate benches/landing zones, maintain regional and pad-scale tops/grids with uncertainty envelopes.
- I.3 — Petrophysical integration: partner with petrophysics to derive porosity, saturation, TOC, kerogen type/maturity; QC NMR, density–neutron, resistivity, spectroscopy, and image logs.
- I.4 — Geomechanics for fracability: estimate Young’s modulus, Poisson’s ratio, UCS, and in-situ stresses to support stage spacing, cluster design, and parent–child mitigation.
- I.5 — Landing/well path design: prescribe target windows, geo-hazards, and well trajectories; deliver pre-drill geologic prognosis and anti-collision/spacing constraints.
- I.6 — Geosteering: provide 24/7 or business-hours steering using LWD/MWD (GR, resistivity, images) against the model; update targets and send look-ahead guidance.
- I.7 — Frac design support: translate brittleness/natural fracture intensity and stress contrasts into stage count, cluster count, proppant/fluid systems in concert with completions.
- I.8 — Diagnostics & surveillance: interpret microseismic, fiber DAS/DTS, tracers, DFITs; reconcile with RTA/PTA and frac hits to refine the geologic/geo-mech model.
- I.9 — Core & lab programs: design coring, plug selection, and lab tests (XRD, MICP, SEM, NMR, Rock-Eval, CT); tie rock properties to logs and mechanical behavior.
- I.10 — Hazard identification: map faults, karst, over-pressured streaks, water-bearing intervals, and H2S; provide drilling notes and mud weight windows (with drilling).
- I.11 — Development planning: contribute to spacing/stacking pilots, section development (cube development), and depletion sequencing with reservoir/completions.
- I.12 — Data stewardship: curate well headers, tops, markers, facies, and grids; ensure WITSML and corporate datastores are clean, versioned, and auditable.
II. Required Skills & Physical Demands
II.A Technical Skills
- II.1 — Tight-reservoir stratigraphy and facies analysis; thin-bed recognition and bench delineation.
- II.2 — Petrophysics for low-perm systems: Archie/dual-water, NMR interpretation, capillary pressure scaling, SCAL integration.
- II.3 — Geomechanics: dynamic-to-static conversions, stress inversion from logs/DFITs, natural fracture characterization, frac-barrier assessment.
- II.4 — Seismic interpretation: attribute analysis, fault/fracture extraction, depth conversion, AVA/AVO screening where applicable.
- II.5 — Geosteering and wellbore imaging: structure/facies steering, dip picking, bed boundary detection.
- II.6 — Unconventional diagnostics: microseismic QC/interpretation, tracers, fiber DAS/DTS, pressure interference, RTA pattern recognition (linear/bilinear/transition flow).
- II.7 — Data analytics/GIS: spatial statistics, uncertainty handling, domain-specific ML feature engineering (estimated for some teams).
- II.8 — Rock physics: elastic property estimation from sonic/density; brittleness and mineralogical proxies.
II.B Soft Skills
- II.9 — Cross-discipline collaboration with drilling, completions, petrophysics, reservoir, and production ops.
- II.10 — Rapid decision-making under time pressure during geosteering and frac ops.
- II.11 — Clear communication of uncertainty and operational implications.
- II.12 — Data hygiene, version control, and reproducible workflows.
II.C Physical Demands
- II.13 — Predominantly office-based; periodic rig/site visits requiring PPE, ladder climbs, and long days.
- II.14 — Ability to work extended hours during drilling/completions campaigns and night-shift rotations for steering (as assigned).
III. Tools, Software, and Equipment
- III.1 Subsurface interpretation: Petrel, DecisionSpace/OpenWorks, Kingdom, Petra; seismic attributes and fault/fracture extraction modules.
- III.2 Petrophysics: Techlog, Interactive Petrophysics; Python/R notebooks for custom saturation/TOC workflows.
- III.3 Geomechanics: RokDoc/JewelSuite/Techlog Geomechanics; DFIT/G-function utilities; Mohr-Coulomb/Mogi-Coulomb toolkits.
- III.4 Frac modeling (interface): GOHFER, StimPlan, MFrac/ResFrac (for geologic/geo-mech inputs and interpretation).
- III.5 RTA/PTA: KAPPA (Saphir/Emeraude), Harmony Enterprise for flow regime diagnostics and depletion trends.
- III.6 Geosteering: StarSteer/WellArchitect/GeoSteer; real-time WITSML viewers; LWD image interpretation.
- III.7 Diagnostics: Microseismic interpretation suites; fiber DAS/DTS visualization; tracer analytics dashboards.
- III.8 GIS/Visualization: ArcGIS/QGIS, Spotfire/Power BI for pad/section development and surveillance maps.
- III.9 Lab/rock characterization: XRD/XRF, SEM/FIB-SEM, CT scanners, MICP systems, NMR, Rock-Eval pyrolysis.
- III.10 Data management: Corporate E&P datastores, well header/top databases, WITSML servers, version control.
IV. Work Environment
- IV.1 — Primarily onshore unconventional basins; office-based with field visits to rigs/pads and core labs.
- IV.2 — Support model: business hours with on-call during drilling/completions; or designated 12-hr shifts for geosteering (days/nights).
- IV.3 — Travel: regional field travel for wells in execution; occasional vendor/lab visits; conferences as approved.
- IV.4 — HSE: compliance with site inductions, permit-to-work awareness, and hazard communication for subsurface risks.
V. Reporting Lines & Interfaces
- V.1 Reports to: Geology Team Lead or Subsurface/Asset Development Manager.
- V.2 Direct interfaces:
- Petrophysicists — log interpretation, saturation/TOC, elastic properties.
- Geophysicists — seismic attributes, depth conversion, fault risk.
- Reservoir engineers — RTA/PTA integration, depletion/spacing pilots, material balance context.
- Drilling engineers — well planning, mud weights, hazards, anti-collision.
- Completions engineers — frac stage/cluster design, fluid/proppant selection, diagnostics.
- Production/Operations — flowback surveillance, interference, water management.
- Data management/Analytics — data quality, dashboards, ML pilots (estimated in some orgs).
- Land/Regulatory/HSE — lease lines, setbacks, subsurface risk communication.
- V.3 Deliverables & handoffs:
- Pre-drill package: strat model, markers, targets, hazards, mud window, uncertainty.
- Real-time steering notes: target updates, dips, structural corrections.
- Frac-ready geologic model: brittleness/stress maps, barriers, natural fracture trends.
- Post-well wrap: as-drilled vs prognosis, lessons learned, model updates.
- Development packs: spacing/stacking maps, parent–child plans, surveillance layouts.
VI. Career Ladder & Advancement
VI.A Typical progression
- VI.1 — Geologist ? Senior Geologist (asset) ? Staff/Principal Geologist ? Subsurface Lead ? Asset Development Manager (technical track may extend to Chief Geologist).
- VI.2 Requirements to advance: delivery of multi-well pads, demonstrable uplift from geo-informed frac/well placement, cross-discipline leadership, and stewardship of pilots (spacing/stacking, diagnostics).
VI.B Deliverables & Interfaces (role-centric)
- VI.3 Primary outputs: maps/grids, well target files, geo-mechanical property cubes, steering decks, post-frac interpretations, and subsurface risk registers.
- VI.4 Interfaces: routine technical reviews with subsurface/completions; daily rig call participation during execution; stage-by-stage frac room support as needed.
VI.C Toolchain Snapshot
- VI.5 — Interpretation: Petrel/DecisionSpace/Kingdom/Petra; GIS: ArcGIS/QGIS.
- VI.6 — Petrophysics/Geomech: Techlog/IP, RokDoc/JewelSuite; Diagnostics: KAPPA, Harmony, microseismic/DAS suites.
- VI.7 — Geosteering: StarSteer/WellArchitect; Frac interface: GOHFER/StimPlan/MFrac/ResFrac.
- VI.8 — Lab: XRD/XRF, SEM/FIB-SEM, MICP, NMR, CT; Data: WITSML/corp stores, Spotfire/Power BI.
VI.D Progression Trigger
- VI.9 — Typically promoted after delivering 4–6 pads (20–40 wells) with measurable EUR/frac-efficiency uplift, plus leading a spacing/stacking or diagnostics pilot; recognized competency in geosteering and geomechanics; internal technical certification or peer review completion (estimated thresholds vary by operator).
Key Equations & Tight-Reservoir Diagnostics (selected)
- Archie (clean formations): \( S_w^n = \dfrac{a\,R_w}{\phi^m\,R_t} \)
- Elastic properties (dynamic):
\( E = \rho\,V_s^2 \dfrac{3V_p^2 - 4V_s^2}{V_p^2 - V_s^2}, \quad \nu = \dfrac{V_p^2 - 2V_s^2}{2\,(V_p^2 - V_s^2)} \)
- Brittleness (mineralogical proxy): \( BI_{\text{min}} = \dfrac{\text{Quartz} + \text{Carbonate}}{\text{Quartz} + \text{Carbonate} + \text{Clay}} \)
- Linear-flow signature (RTA): half-slope on log-log derivative; characteristic length growth with time:
\( x_{\text{eff}} \propto \sqrt{\dfrac{k\,t}{\phi\,c_t\,\mu}} \)
- Minimum horizontal stress (simplified):
\( \sigma_{h,\min} \approx \dfrac{\nu}{1-\nu}\,(\sigma_v - \alpha P_p) + \alpha P_p + \Delta\sigma_{\text{tect}} \) (inputs refined with DFIT and logs)
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