SCIENCE · INVESTIGATE AND EXPLAIN

Combine petroleum-system history with a bounded pore inventory

Organic-rich source material can generate hydrocarbons during burial and heating. Migration, porous reservoir rock, a sufficiently effective seal and a trapping geometry must align in time for accumulation. Coal represents a different concentrated organic deposit history; not every fossil fuel occupies a conventional porous trap.

Learning outcome: Hold geometry fixed while changing closure history, then vary porosity under early closure. Preserve the age ordering, volume-factor direction and separate retained/recoverable quantities. List a new observation that would test the no-recharge assumption.

Starting recap

Retain resource inventories, physical force and reaction boundaries, chronological alternatives and explicit decision constraints. Conditional teaching results do not certify actual site suitability.

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Try

At porosity 0.2 and early closure, pore volume is 400000 m³; hydrocarbon capacity is 300000 reservoir m³, equivalent to 250000 surface m³. Applying recovery 0.3 gives 75000 surface m³. These units are not interchangeable.

Open the experiment

Predict

Can identical present-day porosity and trap shape imply different retained inventories because of timing?

Your prediction and reason

Experiment

Hold geometry fixed while changing closure history, then vary porosity under early closure. Preserve the age ordering, volume-factor direction and separate retained/recoverable quantities. List a new observation that would test the no-recharge assumption.

Combine pore inventory with trap timing

Worked teaching model · synthetic values · Original reservoir bulk volume 2 million m³, water saturation 0.25, formation volume factor 1.2 reservoir m³ per surface m³. Recovery fraction 0.3. Charge pulse at 80 Ma; closure at 100 Ma (before) or 60 Ma (after). Late closure retains no pulse in this deliberately open escape model; no later recharge.

Effective porosity: 0.2 fraction Timing: closure before charge 0 / after charge 1: 0 code

Reset keeps your prediction, captures and practice history.

Porous rock is not sufficient: source, migration, seal, trap and timing must be compatible.

The calculation stipulates full charging for the early closed trap and none for the late open one. Real migration can continue or recur; reservoir volume alone does not prove a discovery, reserve, economic viability or permission to extract.

Chronology: Closure at 100 Ma precedes charge at 80 Ma: pulse retained up to supplied capacity.

Complete conditional quantities, with separate units
Quantity	Value	Unit
Pore volume	400000	m³
Geometric hydrocarbon-filled capacity	300000	reservoir m³
Charge retained under supplied timing	1	0 no / 1 yes
Retained surface-equivalent inventory	250000	surface m³
Conditional recoverable amount	75000	surface m³

Original instructional packets and diagrams, not actual site measurements, legal limits or professional clearance.

Porous rock is not sufficient: source, migration, seal, trap and timing must be compatible.

Observation to attach to a capture

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

1. Define the evidence and process

2. Connect mechanism, geometry and boundary

Porosity gives the fraction of bulk rock occupied by pores; permeability concerns connected flow. A porous reservoir can still lack an effective migration pathway or retaining seal. Structural traps can arise from folds or faults, while stratigraphic changes can create a reservoir termination. These interpretations require spatial and chronological evidence, not a single porosity measurement.

The original reservoir has bulk volume 2 million m³, porosity a and water saturation 0.25. Hydrocarbon-filled capacity is bulk volume × a × 0.75. Divide by formation volume factor 1.2 reservoir m³ per surface m³ to compare with a stipulated surface inventory; applying recovery fraction 0.3 is a further conditional step, not a new measurement.

A single charge pulse occurs at 80 Ma. Closure at 100 Ma is earlier in time and permits retention up to the specified capacity; closure at 60 Ma is later and the pulse escapes in this intentionally simplified history. Real systems may recharge or leak, so an empty late-trap result is conditional on no subsequent charge. No inventory here is an actual discovery, reserve declaration or extraction recommendation.

3. Reconstruct the worked packet

4. Predict and investigate

Predict first: Can identical present-day porosity and trap shape imply different retained inventories because of timing?

5. Test changed evidence

Apply the evidence to a changed case

At porosity 0.3, compare closure at 100 Ma and 60 Ma for the single 80 Ma pulse.

Retain the evidence frame, calculations and assumptions before opening public feedback.

Compare a worked response

Pore capacity is 600000 m³ and geometric hydrocarbon capacity 450000 reservoir m³ in both cases. Early closure retains 375000 surface m³ and conditionally recovers 112500. Late closure retains zero in this open-escape/no-recharge model, despite unchanged geometry.

6. Retain a bounded decision

Preserve the first plan, source identity, original observations, units and competing interpretations. All numerical packets and diagrams in this category are invented teaching cases, not measured site conditions. Retain earlier actual USGS archives separately; do not merge unrelated sites into an invented actual history. Human review, unfamiliar transfer and any chosen supervised practical pathway remain separate. No mining, treatment, slope access or environmental clearance is authorized by these exercises.

Mechanism reference, checked 30 October 2026. Original prose, calculations, questions and diagrams.

Apply

Public practice checks a specific claim. It does not establish independent mastery.

At porosity 0.3, compare closure at 100 Ma and 60 Ma for the single 80 Ma pulse.

Your explanation and limitations

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

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