The Framework 

Subsurface and engineered energy systems are governed by a small number of fundamental physical constraints. Across upstream energy, energy transition (e.g., CCS, hydrogen storage, geothermal), and infrastructure (e.g., pipelines, storage, hubs), project success ultimately depends on whether a small set of interrelated conditions can be met—at the right scale, at the right cost, and with acceptable risk.

The aim of the framework is to make those conditions explicit, so technical teams and decision-makers can move from evidence → assumptions → scenarios → investment decisions with traceability.

Where this Applies

• Upstream energy: exploration risking, appraisal, development concept selection, brownfield optimisation
• CCS: site screening, injectivity/capacity/containment, monitoring and regulatory readiness
• Hydrogen storage: cavern or porous media storage, cycling performance, integrity and safety cases
• Geothermal: heat-in-place, deliverability, reservoir sustainability and operational constraints
• Infrastructure: CO2/H2/gas networks, pipelines, hubs, storage and interconnectors (capacity, operability, integrity)

How to Use the Framework

Use the constraints as a disciplined sequence: (1) state the evidence you have, (2) make the minimum set of assumptions required to proceed, (3) express uncertainty as a small number of scenarios (downside/base/upside or alternative geological models), and (4) link each scenario to decisions (advance/hold/drop; design choices; data acquisition). The output is a traceable decision narrative and a focused value-of-information data plan: what to measure next, why it matters, and what decision it will change.

The Subsurface Constraints Framework

This framework does not attempt to capture every factor relevant to investment decisions. Strategy, policy and regulation, delivery capability, commercial structure, stakeholder/community context, financing conditions, and market interfaces (e.g., power and carbon markets) remain essential. Its purpose is narrower and more precise: to evaluate the physical subsurface and flow-system constraints that govern what is possible, what is likely, and what is bankable.

Resource/Supply (Charge), Storage/Containment (Reservoir), Fluids & Flow Behaviour, and Pressure/Integrity.

These constraints determine whether a resource exists (or can be delivered), whether it can be stored or contained at useful scale (e.g., hydrocarbons, geothermal heat, CO2/H2 storage), and whether it can be moved through the system safely and economically (subsurface, wells, pipelines, and facilities).

This page introduces a Constraints Framework for connecting physical reality to capital decisions—applicable across upstream energy, the energy transition, and infrastructure.

1. Resource / Supply (Charge)

The first constraint is whether there is a resource or supply available at the scale and quality needed—either naturally present (e.g., hydrocarbons, geothermal heat) or deliverable into the system (e.g., captured CO2 for storage, hydrogen for storage and transport).

In upstream petroleum, “charge” depends on generation, migration, and timing from source rocks into traps. In geothermal, it relates to heat-in-place, recharge, and deliverability. In CCS and subsurface storage, it is the availability, purity, and continuity of injected streams (CO2/H2) and the ability to sustain injection over time. In all cases, the question is the same: is there enough of the right thing, in the right place, at the right time?

Without a credible resource/supply basis, downstream design work is optimisation without a foundation.

2. Storage / Containment (Reservoir)

The second constraint is whether the system can store, contain, and transmit fluids and energy in a controlled way—within porous rock, engineered caverns, depleted fields, or connected infrastructure.

In petroleum, reservoir quality (porosity, permeability, connectivity, architecture) determines recoverable volumes and deliverability. In CCS and hydrogen storage, the equivalent questions are capacity, injectivity/withdrawal performance, containment, and plume/pressure management. In infrastructure, it extends to the capacity and connectivity of the network (hubs, pipelines, storage) that enables delivery.

Even with strong resource/supply, weak storage/containment characteristics (or poorly understood connectivity) can cap performance and undermine the investment case.

3. Fluids & Flow Behaviour

Energy projects are governed by how fluids behave and how they flow through subsurface, wells, pipelines, and facilities.

Temperature, pressure, and composition determine phase behaviour (oil/gas/condensate, supercritical CO2, dense-phase CO2, H2 embrittlement considerations, brine chemistry) and therefore drive recovery mechanisms, injectivity, corrosion/scale risk, and surface processing requirements. In infrastructure, these same factors show up as flow assurance, compression needs, materials selection, and operating envelopes.

Understanding fluid and flow behaviour is essential for predicting performance, defining operating limits, and avoiding avoidable cost and safety surprises.

4. Pressure / Integrity

Pressure governs flow, integrity, and operability—both in the subsurface and across connected infrastructure.

In upstream, pressure regimes influence drilling risk, deliverability, and recovery. In CCS and subsurface storage, injection-induced pressure must be managed to protect containment (caprock integrity and fault stability) and to remain within regulatory constraints. In infrastructure, pressure management governs throughput, compression power, linepack, and safety margins.

Effective lifecycle management requires understanding how pressure evolves, what it implies for integrity, and what monitoring is needed to stay inside the safe operating envelope.

The Decision Chain

Every stage of subsurface evaluation ultimately assesses these four constraints.

From basin evolution and petroleum system analysis to reservoir modelling and economic evaluation, the objective is to determine whether physical conditions support performance and whether that performance justifies capital investment. The same logic applies to transition projects (CO2 storage, geothermal, hydrogen storage) and enabling infrastructure (pipelines, hubs, storage) where subsurface capacity, flow behaviour, and integrity ultimately govern deliverability and risk.

This framework follows the decision chain, examining how physical constraints translate into operational performance and investment outcomes across the full lifecycle—from early screening and concept selection to delivery, monitoring, and adaptation.