Project Design, Reservoir Surveillance, and Optimization of CO₂ Enhanced Oil Recovery Floods — Worldwide
Assign your company's CO₂ flooding EOR project — from initial feasibility screening through field-wide surveillance and optimization — to A&A, and let the high-level, seasoned CO₂ EOR consultants of the A&A Consulting Team put more than fifty years of hands-on CO₂ flood experience to work for you.
Avasthi & Associates, Inc. (A&A) is an independent petroleum engineering consulting firm. A&A does not sell CO₂, injection equipment, or logging/surveillance tools — our only business is expert technical consulting, which means our CO₂ flood design and surveillance recommendations are never influenced by a stake in any particular vendor or technology.
A&A's CO₂ EOR Project Experience
Several high-level, seasoned consultants of the A&A Consulting Team have been working on CO₂ EOR projects since the 1970s, and during this time have worked on some of the major CO₂ EOR projects in several regions of the United States, including, but not limited to:
• The Permian Basin (West Texas and Eastern New Mexico)
• The Gulf Coast region (Texas, Louisiana, Mississippi, and Alabama)
• The Rocky Mountain region
• The Williston Basin
Several high-level, seasoned consultants of the A&A Consulting Team have also been involved in CO₂ EOR projects in other countries, including, but not limited to:
• Canada
• Argentina
• Indonesia
• Vietnam
A&A's CO₂ EOR Consulting Services
A&A Consulting Team's extensive CO₂ EOR project experience includes, but is not limited to, conducting:
• CO₂ EOR project scoping/feasibility studies
• Pilot-test CO₂ EOR project design, evaluation, and optimization studies
• Field-wide CO₂ EOR project design, evaluation, and optimization studies
• CO₂ EOR project surveillance
Training & Knowledge Transfer
The high-level, seasoned CO₂ EOR consultants of the A&A Consulting Team have not only worked on all aspects of CO₂ EOR projects for more than fifty years, but have also provided training to the professional and managerial staff of client companies, around the world, on “Practical Engineering Aspects of CO₂ Injection for EOR and CCS/CCUS/CO₂ Geosequestration.” An outline of this customized training workshop, which can be conducted at our clients' offices around the world whenever mutually convenient, is available on request.
A&A's high-level, seasoned CO₂ EOR consultants, along with other CO₂ EOR industry veterans, also volunteer their time and effort to train the next generation of engineers in CO₂ EOR technologies and practices, teaching two popular public training courses, around the world, under the auspices of the Society of Petroleum Engineers (SPE):
• Practical Aspects of CO₂ Flooding EOR and CO₂ Geosequestration
• CCUS/Geological Sequestration of CO₂
Since 2004, more than 600 members and non-members of SPE have attended these two popular public training courses, or the expanded, customized versions of these courses offered by A&A, around the world.
Reservoir Surveillance of CO₂ Floods
Surveillance of CO₂ floods is critical to maximizing oil recovery. Injection and production profiles are used to determine the inflow and outflow of fluids into the various layers of the reservoir. Radioactive tracer logs are often used for this purpose: a slug of radioactive tracer (typically Iodine-131) is added to the injection fluid, and as the slug moves down the well, several gamma-ray logs are recorded at specific time intervals. The reduction in tracer material as it moves down the wellbore indicates how much of the injected fluid goes into each zone. The position of the tracer slug appears as a large gamma-ray spike whose size is proportional to the flow rate; a reduction in the size of the peak indicates a loss of fluid into the formation. Fluid velocity can also be calculated from the time interval and the distance the peak has moved, using time-slug analysis. Radioactive tracers can also be used to detect channels and leaks within the casing and cement jobs — correcting these wellbore-integrity issues is critical to maximizing vertical sweep.
Tracer logs can also be used to determine inflow from the producing zones, with the tool operated in reverse mode relative to an injection profile. Capacitance sensors are installed to determine the percentage of oil and water flow from each zone: the dielectric constant of water (about 80) is so high relative to that of oil (about 1.9 to 2.3) that the capacitance reading is a direct indicator of the amount of water present.
In addition to inflow and outflow from wellbore perforations, the breakthrough of CO₂ provides an indication of sweep efficiency. Dimensionless curves can be generated for the various injection patterns, and poorly performing patterns can be identified; deviation from normal flow behavior indicates that the injector and offset producers should be investigated for potential mechanical-integrity issues. Adjustment of injection and production flow rates can also be used to maximize areal sweep, based on formation thickness and pattern size.
For relatively mature CO₂ floods, 3-D seismic has been used to determine areal sweep. Operators often overlook the fact that CO₂ can migrate downdip toward plugged and abandoned wells; should this occur, and those wells have mechanical-integrity issues, extreme losses of CO₂ can result. Reservoir pressure in all parts of the reservoir should therefore be monitored closely.
Designing CO₂ Floods in Reservoirs with Strong or Limited Aquifers
In the U.S. Gulf Coast region, and in many other parts of the world, some of the largest oil reservoirs have strong waterdrive aquifers that assist in maintaining reservoir pressure during primary production. While these aquifers may seem virtually inexhaustible, they are often insufficient to maintain pressure at original discovery levels, and reservoir pressure frequently drops below MMP (Minimum Miscibility Pressure). While good oil recoveries have been achieved by conducting CO₂ floods below MMP, it is desirable to pressure up the reservoir as high as possible — ideally above MMP — to achieve maximum oil recovery.
A&A consultants have direct field experience with this challenge, having raised reservoir pressure via water injection in an actual field demonstration (SPE-144961-MS, “Large Scale CO2 Flood Begins Along Texas Gulf Coast,” presented at the 2011 SPE Asia Pacific Enhanced Oil Recovery Conference, Kuala Lumpur, Malaysia, 19–20 July 2011). In that project, large volumes of water leaked off into the aquifer during the re-pressurization process — a condition that can persist for many years, at rates as high as 200,000 to 300,000 BWPD in the applicable fields. The design was effective in raising reservoir pressure and reducing the volume of CO₂ purchased, but water-injection costs were significant and often required large volumes of make-up water produced from other water-bearing sands. In the case described, a nearby producing offset field also experienced reduced aquifer pressure, compounding the problem. All of this must be considered when designing CO₂ floods in reservoirs with strong or limited aquifers, in the U.S. Gulf Coast region and in many other parts of the world.
A reservoir type that is often overlooked, due to its low reservoir pressure at the time of CO₂ flooding, is the depletion-drive reservoir. Depletion-drive reservoirs contain higher oil saturations than waterdrive reservoirs and can be pressured up with CO₂. The salt-dome fields of the U.S. Gulf Coast region are ideal candidates for CO₂ flooding, since many of their small fault blocks had limited aquifers and therefore experienced low oil recoveries during primary production. These small fault blocks were also poor waterflood candidates, due to the inability to establish good injection patterns to improve sweep. Continuous CO₂ injection, by contrast, offers clear advantages for maximizing oil recovery from these isolated fault blocks: the reservoir can be pressured up with CO₂, and the wells then flowed back while recycling CO₂ to maintain reservoir pressure. The CO₂ moves to the boundaries of the fault block and contacts more oil than could be achieved by water injection. The key parameters for successfully flooding these reservoirs are good fault seal and the ability to pressure up the reservoir; material balance is used during the re-pressurization process to determine the pore volume impacted by injection, and to account for any CO₂ that leaks into an adjacent fault block.
A&A consultants have screened numerous oil fields in the U.S. Gulf Coast region for reservoirs amenable to successful CO₂ flooding, and can assist your company with screening/scoping/feasibility studies and CO₂ flood project design studies for reservoirs with strong or limited aquifers, in the Gulf Coast region and elsewhere around the world.
What A&A Delivers
A CO₂ flooding EOR engagement with the A&A Consulting Team is built around the practical decisions your company needs to make, including, but not limited to:
• A CO₂ EOR project scoping/feasibility study, including reservoir screening and MMP/aquifer-strength considerations specific to your candidate fields
• Pilot-test or field-wide CO₂ flood design, evaluation, and optimization, supported by reservoir simulation and facilities studies
• A reservoir-surveillance program — tracer logging, capacitance-based inflow/outflow analysis, and 3-D seismic sweep monitoring — to track performance and identify wellbore-integrity issues before they become costly
• Presentation-ready recommendations and economic justification for your company's management, partners, and investors
To put teams of A&A's high-level, seasoned CO₂ EOR consultants — with extensive experience in reservoir simulation, facilities, and related studies — to work on your company's CO₂ EOR project scoping/feasibility studies, pilot-test or field-wide design, evaluation, optimization, and reservoir-surveillance projects, around the world, please contact us.
In addition, we will be delighted to conduct customized training workshops on any of these topics at your company's offices, around the world, whenever mutually convenient — an outline is available on request.
