Blog · RFour Energy
Technical notes
and field tutorials.
Articles on reservoir engineering, production surveillance, decline analysis, and applied machine learning in upstream oil & gas. Written for engineers who want to understand the physics, not just run the calculation.
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Organizing Subsurface & Production Teams for Mature Fields
A mature field needs a mature organization — not a Geology–Reservoir–Production hierarchy, but a
light matrix of three value streams: base management (surveillance, workovers, bypassed pay, water
handling), development & well delivery (infill, recompletions, fracturing), and modeling,
planning & asset development (models, reserves, FDP). Plus one integrated forecast, a governance
rhythm, and the accountability boundaries that keep opportunities from falling between the boxes.
When the Protocol Passes and the Answer Is Wrong
Four ways a machine-learning result on production data can be wrong while every validation
check reports success — a baseline nobody asked, a model that structurally cannot
extrapolate, a score that measured the choosing rather than the model, and a feature that
contained its own answer. Each one measured on a five-well gas history, with the five
questions that catch them.
Reverse Engineering, DoE & Machine Learning in Reservoir Engineering
From observed field behavior back to mechanism: inverse problems and history matching,
experimental design (factorial, LHS, response surfaces), ML surrogates and explainability,
and the tool-assisted agentic AI loop — plus a step-by-step Python stack and the anatomy of
an exception-based surveillance dashboard, all under physics-first governance.
Everything below is grouped by subject and ordered newest first within each group. The three posts above also appear in their own section — they are repeated here, not moved.
Geoscience Foundations 2
Where the rock and the seismic come from, for engineers.
Regional Geology for Non-Geologists
Reading a basin's story in plain language — the petroleum system, basin types from plate
tectonics, stratigraphy and unconformities, structural traps, and how to read a
cross-section. No degree required.
Seismic for Non-Geophysicists
An ultrasound of the earth. The echo principle, acoustic impedance, two-way time versus
depth, stacking and migration in plain words, and how to read horizons, faults, and bright
spots on a section.
Petrophysics & Characterization 2
Turning logs and core into properties a model can use.
Low-Resistivity Pay (LRLC) and Low-Quality Reservoir (LQR)
Two different failures with one symptom: pay that hides because the log lacks contrast, and pay that hides because the rock cannot flow. Saturation models, pore-throat classification, capillarity, and the test that separates them.
Rock Typing Reimagined
Building a Python, agentic AI, Excel, and dashboard framework for modern reservoir
characterization. Six methods, one platform — Winland R35, FZI/HFU, PGS,
Modified Lorenz, Leverett J-function, and ML on logs. Where the calculations end
and the interpretation begins.
Reservoir Engineering 2
Material balance, recovery mechanisms, and the tank behind the wells.
Enhanced Oil Recovery — A Complete Guide
Thermal (steam flooding, SAGD, in-situ combustion), gas and miscible (CO₂, N₂,
hydrocarbon), and chemical (polymer, surfactant, ASP) methods on one map —
recovery mechanisms, screening criteria, and when each method actually pays.
The Complete Guide to Gas Material Balance Analysis
How to estimate OGIP and identify drive mechanism from pressure decline. P/Z plot,
Cole plot, Roach plot, aquifer modeling across four classical models, and three worked
numerical examples spanning volumetric, water drive, and geopressured reservoirs.
Production Engineering 7
Diagnosing and improving what individual wells actually do.
Workover & Well-Service Candidate Selection — A Systematic Workflow
Choosing the right well and the right intervention: a physics-first, multidisciplinary
workflow from production gap to risked-value ranking — integrating G&G, reservoir, and
production engineering. Includes nodal analysis, a diagnosis-to-intervention map, and deep
dives on artificial-lift selection, sand control, and water shut-off screening — with a full
end-to-end workflow chart from team and data through methodology to well-program type.
Reading the Whole Production System
A practitioner's guide to nodal analysis. Where IPR meets VLP, why the operating point
is never decided at any single component, and how to translate seventy years of
correlations into something that runs on your laptop. Equations kept to what's useful,
references kept honest, opinions kept brief.
Reciprocal Rate Method — reserves from rate-time data alone
When Arps hyperbolic fits over-extrapolate by 40% or more, the reciprocal rate plot
offers a theoretically rigorous second opinion. Plot 1/q vs Np/q, fit a line,
take the inverse slope. Worked example, log-log cross-check, and the factor-of-2 caveat
for gas wells.
Ershaghi X-Plot — waterflood performance & ultimate recovery
Mature waterfloods need a different forecasting tool than rate-time decline. Ershaghi's
log-WC vs cumulative oil linearization extracts ultimate recovery directly from data
the operator already has. Worked example, window selection, and engineering override.
Chan diagnostic plot — reading water production mechanisms
Coning, channeling, or near-wellbore problem? Chan's 1995 diagnostic plot turns
water-oil ratio time series into a mechanism identification tool. Read it correctly
and the workover plan writes itself.
Arps decline curve analysis — a practical guide
When to use exponential, hyperbolic, or harmonic. How to read the b-factor as reservoir
physics. Window selection, terminal decline switch, and common pitfalls when forecasting
EUR.
Understanding Coleman-Turner Critical Rate for Gas Wells
Gas wells don't fail because the reservoir runs dry — they fail because liquids start
winning the upward race. A practical guide to the equation, the physics behind it,
and how to read the safety ratio in the field.
Reserves & Economics 2
Counting what is there, and how confident that count is.
Reserves Classification — A Systematic Guide to PRMS
The complete, systematic framework under SPE-PRMS 2018 — the two-axis classification matrix,
Reserves vs Contingent vs Prospective Resources, 1P/2P/3P and P90/P50/P10, project maturity
sub-classes, the commerciality test, probabilistic aggregation, and how PRMS relates to SEC
and UNFC.
Hydrocarbon Reserves in Probabilities
Why P50 isn't enough — and how Monte Carlo Simulation transforms volumetric reserves
estimation. Probabilistic OGIP/OOIP, choosing the right distribution per parameter,
multi-zone aggregation, tornado analysis, and the upcoming MCVR tool.
Data Science & ML 3
Where statistics and machine learning earn their place — and where they do not.
When the Protocol Passes and the Answer Is Wrong
Four ways a machine-learning result on production data can be wrong while every validation
check reports success — a baseline nobody asked, a model that structurally cannot
extrapolate, a score that measured the choosing rather than the model, and a feature that
contained its own answer. Each one measured on a five-well gas history, with the five
questions that catch them.
Reverse Engineering, DoE & Machine Learning in Reservoir Engineering
From observed field behavior back to mechanism: inverse problems and history matching,
experimental design (factorial, LHS, response surfaces), ML surrogates and explainability,
and the tool-assisted agentic AI loop — plus a step-by-step Python stack and the anatomy of
an exception-based surveillance dashboard, all under physics-first governance.
AI & Machine Learning in Upstream Oil & Gas
A complete, systematic tour across the upstream value chain — seismic fault-detection CNNs,
facies classification, surrogate reservoir models, drilling analytics, production forecasting and
ESP failure prediction — plus the physics-informed turn, the real MLOps workflow, and the
subsurface-specific pitfalls (leakage, tiny data, extrapolation) that sink naive models.
Field Development & Asset Management 2
Turning a discovery into a plan, and a plan into an organisation.
Organizing Subsurface & Production Teams for Mature Fields
A mature field needs a mature organization — not a Geology–Reservoir–Production hierarchy, but a
light matrix of three value streams: base management (surveillance, workovers, bypassed pay, water
handling), development & well delivery (infill, recompletions, fracturing), and modeling,
planning & asset development (models, reserves, FDP). Plus one integrated forecast, a governance
rhythm, and the accountability boundaries that keep opportunities from falling between the boxes.
From Exploration Well to Development Plan — The Reservoir & Petroleum Engineer’s Role
An exploration well is drilled once, at great cost. How reservoir and petroleum engineers shape it
across the lifecycle — well objectives and a data-acquisition plan, pre-drill P90/P50/P10 volumetrics
and the pressure prognosis behind well design, the data event of drilling and well testing (kh, skin,
deliverability), then reserves under PRMS, concept selection, production forecasts and the Field
Development Plan.
Geothermal 1
The same reservoir physics, a different working fluid.
More articles coming.
Topics in the pipeline: physics-informed ML for well health classification, intermittent producer detection, field-scale intervention ranking, and multi-zone correlation for probabilistic reserves.
Topics in the pipeline: physics-informed ML for well health classification, intermittent producer detection, field-scale intervention ranking, and multi-zone correlation for probabilistic reserves.