CO2 Storage in Depleted / Depleting Oil and Gas Fields
Site Characterization, Legacy Well-Integrity Evaluation, and Storage-Performance Modeling for CO₂ Geologic Sequestration in Produced Reservoirs — Worldwide
Assign your company's depleted or depleting oil and gas field CO₂ storage project to A&A, and let the high-level, seasoned consultants of the A&A Consulting Team characterize, model, and de-risk your storage site — from initial site selection and legacy well-integrity evaluation, through injection design and long-term containment verification.
Avasthi & Associates, Inc. (A&A) is an independent petroleum engineering and geoscience consulting firm. A&A does not sell CO₂, injection equipment, monitoring technology, or carbon-credit/offset products — our only business is expert technical consulting, which means A&A's CO₂ storage recommendations are never influenced by a stake in any particular vendor, technology, or carbon-market program.
The high-level, seasoned consultants of the A&A Consulting Team have been working on CO₂ projects, around the world, since the 1970s — providing state-of-the-art consulting services on CO₂-EOR, CO₂ storage/geosequestration, and CCS/CCUS projects of every kind. Depleted and depleting oil and gas fields are, alongside deep saline formations, one of the two principal geologic settings for CO₂ storage, and each presents a distinct technical profile. This page covers what is distinctive about storing CO₂ in a produced reservoir; for A&A's full CO₂-EOR and CCS/CCUS practice, and for CO₂ storage in deep saline formations, see the related services below.
Related A&A Service: For A&A's full CO₂-EOR and CCS/CCUS consulting practice — site screening, injection engineering, well design, and MRV — please see A&A's CO₂ EOR + Geosequestration (CCS/CCUS) Consulting page.
Related A&A Service: For A&A's dedicated site characterization and modeling services for the other principal CO₂ storage setting, please see A&A's CO₂ Storage in Deep Saline Formations page.
Why Depleted and Depleting Oil and Gas Fields Are Attractive CO₂ Storage Candidates
• A proven trap: a depleted or depleting oil and gas field held hydrocarbons in place for geologic time, which is strong direct evidence that its seal and trapping geometry can also contain injected CO₂ — a level of confidence a saline formation, with no hydrocarbon history, cannot offer at the outset
• Extensive pre-existing subsurface data: decades of well logs, core data, 3-D seismic, and production/pressure history are typically already available, substantially lowering the cost and uncertainty of site characterization compared to a greenfield formation
• Storage capacity created by hydrocarbon withdrawal: produced oil and gas volume becomes available pore space, and reservoir pressure is typically already below its original, virgin level — providing pressure headroom for CO₂ injection before formation parting pressure is reached
• CO₂-EOR synergy: many depleted and depleting fields can still support economic CO₂ enhanced oil recovery, combining a revenue-generating oil recovery project with permanent CO₂ storage
Related A&A Service: For A&A's full CO₂ flooding EOR technical services and field experience, please see A&A's CO₂ Flooding EOR page.
Characterizing Depleted and Depleting Oil and Gas Fields for CO₂ Storage
The high-level, seasoned consultants of A&A's Geomechanics, Geosciences, Reservoir, and Production Consulting Teams are experts in characterizing every aspect of a depleted or depleting oil and gas field relevant to CO₂ storage, including, but not limited to:
• Site selection: identifying primary and contingency storage sites with sufficient injectivity, storage capacity, and demonstrated ability to contain CO₂ over the long term
• Reservoir characterization: porosity, permeability, heterogeneity, and formation-water salinity
• Seal characterization: seal extent, sealing capacity, and secondary seals, which requires characterization of the overburden as well as the primary seal
• Structural characterization: CO₂ migration potential and likely migration pathways within the storage complex
• Formation mineralogy: reactions between CO₂ and formation minerals, and the potential impact on injectivity and long-term storage security
• Fault characterization: sealing capacity of faults within or bounding the storage complex, and their potential for injection-induced re-activation
• Hydrodynamic characterization: regional formation-water flow direction and rate, which can work for or against long-term plume containment and pressure dissipation
• USDW characterization: identification and characterization of any Underground Sources of Drinking Water (USDWs) that must be protected from CO₂ or displaced brine
Related A&A Service: For A&A's full geomechanical characterization and fault-reactivation-risk services, please see A&A's Geomechanics Consulting page.
The Legacy Well-Integrity Challenge
A depleted or depleting oil and gas field's greatest storage advantage — decades of prior drilling and production — is also its greatest storage risk. Unlike a saline formation with few or no wellbore penetrations, a produced field may have dozens to hundreds of existing wells within or near the storage complex: active producers, injectors, and plugged-and-abandoned (P&A) wells, some completed or plugged decades before CO₂ storage was contemplated. Every one of these wellbores is a potential CO₂ leakage pathway unless it is individually evaluated and, where necessary, remediated — including legacy P&A wells whose cement and plugging materials may predate the CO₂-resistant standards a storage project now requires.
Related A&A Service: For A&A's full life-cycle well-integrity due diligence and Class II vs. Class VI regulatory guidance, please see A&A's CO₂ Injection Wells: Class II vs. Class VI Wells page.
Modeling CO₂ Storage Performance in Depleted and Depleting Oil and Gas Fields
The high-level, seasoned consultants of A&A's Reservoir, Production, and Simulation/Dynamic Modeling Consulting Teams are experts in modeling every aspect of CO₂ storage performance in a depleted or depleting oil and gas field, including, but not limited to, investigating:
• CO₂ injectivity: the number and spacing of Class VI CO₂-injection wells required, lifetime wellbore integrity, and nodal analysis of CO₂-injection wells
• Formation parting pressure: the maximum sustainable injection pressure before the formation fractures
• CO₂ plume modeling: development and migration of the CO₂ plume, and prediction of possible leaks from the sequestration formation
• Reservoir pressure forecast: starting from the field's already-depleted pressure state — a materially different, generally more favorable, modeling starting point than the near-virgin pressure of an undisturbed saline formation
• Multi-scale modeling: representing the storage complex across the spatial and time scales relevant to injection, plume migration, and long-term containment
• Buoyancy and dissolution capacity: CO₂ buoyancy-driven migration beneath the seal, and the capacity of formation water to dissolve injected CO₂ over time
• Rock properties and SCAL data: special core analysis laboratory (SCAL) data — relative permeability and capillary pressure — needed for a defensible storage-performance forecast
• Heterogeneity: reservoir heterogeneity and its impact on injectivity, sweep, and plume shape
• Simulator selection: choosing simulator(s) appropriate to the storage mechanisms involved, including geomechanical and geochemical coupling where required
A depleted or depleting field's decades of production and pressure history also provide a history-matching calibration advantage a saline formation cannot offer.
Related A&A Service: For A&A's full nodal-analysis and PROSPER-modeling services for CO₂-injection wells, please see A&A's Nodal Analysis and PROSPER Modeling page.
Related A&A Service: For A&A's full history-matching methodology and project experience, please see A&A's History-Matching Consulting page.
Software and Technical Tools
A&A's CO₂ storage consultants are expert users of industry-standard geosciences, geomechanical, and reservoir-simulation software, including, but not limited to:
• Petrel, and comparable geosciences and static/geomodeling software, for reservoir, seal, and structural characterization
• ECLIPSE, GEM, IMEX, and tNavigator, for compositional reservoir simulation of CO₂ injection, plume migration, and storage performance
• Coupled geomechanical-simulation software, for fault-reactivation-risk and formation-parting-pressure analysis
• PROSPER, for nodal analysis and well-performance modeling of CO₂-injection wells
• Industry-standard history-matching and uncertainty-analysis software, for calibrating storage-performance forecasts against decades of field production and pressure data
What A&A Delivers
A CO₂ storage engagement with the A&A Consulting Team, for a depleted or depleting oil and gas field, is built around the practical decisions your company needs to make, including, but not limited to:
• A ranked screening of candidate depleted and depleting fields, by storage capacity, injectivity, and containment confidence
• A full site-characterization report — reservoir, seal, structural, mineralogical, fault, hydrodynamic, and USDW — for your primary and contingency storage sites
• A well-by-well legacy well-integrity assessment, identifying which existing wellbores are fit for the storage project as-is, which require remediation, and which pose an unacceptable risk
• A calibrated, history-matched storage-performance model — CO₂ injectivity, plume migration, and pressure forecast — your project can be permitted and financed on
• Injection-well design and Class VI regulatory support
• Presentation-ready findings for your company's management, partners, investors, and regulatory authorities
Frequently Asked Questions
How is CO₂ storage in a depleted oil and gas field different from CO₂ storage in a deep saline formation?
A depleted or depleting field offers a proven trap and decades of pre-existing subsurface data, but also brings a legacy well-integrity challenge that a saline formation, with few or no prior wellbore penetrations, generally does not face. A saline formation typically offers far greater storage capacity, but requires establishing containment confidence without a hydrocarbon trapping history. A&A's dedicated Deep Saline Formations page covers that setting in full.
Can we pursue CO₂-EOR and CO₂ storage in the same field?
Often, yes. Many depleted and depleting fields can support economic CO₂-EOR while also being suitable for dedicated, longer-term CO₂ storage once EOR operations conclude. A&A's CO₂ EOR + Geosequestration (CCS/CCUS) Consulting page covers how these two objectives fit together, including the regulatory distinction between Class II (CO₂-EOR) and Class VI (dedicated storage) wells.
Why does legacy well integrity matter so much for a depleted field storage project?
Every wellbore that penetrates the storage complex — active, idle, or plugged and abandoned — is a potential pathway for injected CO₂ to migrate out of the target formation. Older wells, particularly those plugged before modern CO₂-resistant materials and standards existed, need individual evaluation and, in some cases, remediation before a storage project can proceed with confidence.
How much does prior production history help with storage-performance forecasting?
Substantially. Decades of production and pressure data let A&A's consultants history-match a reservoir-simulation model against real field performance — a calibration advantage a saline formation, with no comparable production history, does not have. This generally reduces both the cost and the uncertainty of the storage-performance forecast.
Does A&A sell CO₂, injection equipment, or monitoring technology?
No. A&A is an independent consulting firm and does not sell CO₂, injection equipment, monitoring technology, or carbon-credit/offset products, so A&A's site-characterization and storage-performance recommendations are never influenced by a stake in any particular vendor, technology, or carbon-market program.
To put the high-level, seasoned geology, geomechanics, reservoir, production, and well-integrity consultants — subject-matter experts (SMEs) — of the A&A Consulting Team, and collaborators, to work on your company's challenging CO₂ storage in depleted or depleting oil and gas field projects, please contact us.
