The Denver Unit CO2 Flood Transforms Former Waterflood Injectors Into Oil Producers
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This paper outlines the results of a comparative study of air- and immiscible CO2 - Water injection based Enhanced Oil Recovery (EOR) processes for a 30+ °API tight, light oil reservoir. This was accomplished by embedding multiple low- permeability core plugs in crushed reservoir core material to create a composite core that was contained in a 1.84 m long core holder. The objectives of this unscaled experimental work were: 1) to understand the suitability of each EOR process for a low permeability reservoir, 2) to define process parameters prior to a potential field pilot, and 3) to understand the relative merits of each EOR process to mobilize light oil from a tight matrix to a fracture network. A detailed experimental investigation was conducted at realistic reservoir conditions to evaluate the feasibility of an air injection-based EOR process. The air injection results were compared with those from an immiscible CO2-Water injection EOR experiment using the same experimental setup and reservoir conditions. Both the air- and CO2 - Water coreflood tests were performed at 10.3 MPa (1500 psig) and 99 °C in a 100 mm diameter, 1.84 m long composite core-holder using 38 mm diameter reservoir core plugs (that represented the matrix) and mounted within the crushed reservoir core material (that represented the fracture); inert helium gas was used to pressure up the core-holder to reservoir pressure. Permeability of the core plugs was from 0.3 to 3 millidarcies, while the permeability of the crushed core material was 1 to 3 Darcies. Air injection was performed as a standard combustion tube test with injection of 2.3 pore volumes (PV) of air to burn 71% of the packed core length (including helium, a total of 4.3 PV of gas injected). The CO2-Water coreflood was performed with the injection of 2.86 PV of CO2 followed by an extended soak period, then a second injection of an additional 2.86 PV of CO2, followed by the injection of 2.6 PV of water. The pre- and post-test core plug measurements of oil saturation show that the air injection process removed significantly larger quantities of hydrocarbons than the immiscible CO2-Water injection process. Relative to the initial conditions of the core plugs for the Air-Injection experiment, 95+ percent of the hydrocarbons were removed; noting that some fraction of original oil was consumed as fuel. In the post-test CO2-Water injection core plugs, oil recovery was in the range of 30 to 55 percent of OOIP. These findings suggest, under an appropriate field design, that both processes have the potential to recover incremental oil from tight reservoirs. However, the air-injection may be better suited to mobilize oil, due to thermal expansion, rather than the CO2 - Waterflood process.
This paper outlines the results of a comparative study of air- and immiscible CO2 - Water injection based Enhanced Oil Recovery (EOR) processes for a 30+ °API tight, light oil reservoir. This was accomplished by embedding multiple low- permeability core plugs in crushed reservoir core material to create a composite core that was contained in a 1.84 m long core holder. The objectives of this unscaled experimental work were: 1) to understand the suitability of each EOR process for a low permeability reservoir, 2) to define process parameters prior to a potential field pilot, and 3) to understand the relative merits of each EOR process to mobilize light oil from a tight matrix to a fracture network. A detailed experimental investigation was conducted at realistic reservoir conditions to evaluate the feasibility of an air injection-based EOR process. The air injection results were compared with those from an immiscible CO2-Water injection EOR experiment using the same experimental setup and reservoir conditions. Both the air- and CO2 - Water coreflood tests were performed at 10.3 MPa (1500 psig) and 99 °C in a 100 mm diameter, 1.84 m long composite core-holder using 38 mm diameter reservoir core plugs (that represented the matrix) and mounted within the crushed reservoir core material (that represented the fracture); inert helium gas was used to pressure up the core-holder to reservoir pressure. Permeability of the core plugs was from 0.3 to 3 millidarcies, while the permeability of the crushed core material was 1 to 3 Darcies. Air injection was performed as a standard combustion tube test with injection of 2.3 pore volumes (PV) of air to burn 71% of the packed core length (including helium, a total of 4.3 PV of gas injected). The CO2-Water coreflood was performed with the injection of 2.86 PV of CO2 followed by an extended soak period, then a second injection of an additional 2.86 PV of CO2, followed by the injection of 2.6 PV of water. The pre- and post-test core plug measurements of oil saturation show that the air injection process removed significantly larger quantities of hydrocarbons than the immiscible CO2-Water injection process. Relative to the initial conditions of the core plugs for the Air-Injection experiment, 95+ percent of the hydrocarbons were removed; noting that some fraction of original oil was consumed as fuel. In the post-test CO2-Water injection core plugs, oil recovery was in the range of 30 to 55 percent of OOIP. These findings suggest, under an appropriate field design, that both processes have the potential to recover incremental oil from tight reservoirs. However, the air-injection may be better suited to mobilize oil, due to thermal expansion, rather than the CO2 - Waterflood process.
This paper seeks answers, through a ‘philosophical’ approach, to the questions of whether enhanced oil recovery projects are purely driven by economic restrictions (i.e. oil prices) or if there are still technical issues to be considered, making companies refrain from enhanced oil recovery (EOR) applications. Another way of approaching these questions is to ask why some EOR projects are successful and long-lasting regardless of substantial fluctuations in oil prices. To find solid answers to these two, by ‘philosophical’ reasoning, further questions were raised including: (1) has sufficient attention been given to the ‘cheapest’ EOR methods such as air and microbial injection, (2) why are we afraid of the most expensive miscible processes that yield high recoveries in the long run, or (3) why is the incubation period (research to field) of EOR projects so lengthy? After a detailed analysis using sustainable EOR example cases and identifying the myths and facts about EOR, both answers to these questions and supportive data were sought. Premises were listed as outcomes to be considered in the decision making and development of EOR projects. Examples of said considerations include: (1) Every EOR process is case-specific and analogies are difficult to make, hence we still need serious efforts for project design and research for specific processes and technologies, (2) discontinuity in fundamental and case-specific research has been one of the essential reasons preventing the continuity of the projects rather than drops in oil prices, and (3) any EOR project can be made economical, if technical success is proven, through proper optimization methods and continuous project monitoring whilst considering the minimal profit that the company can tolerate. Finally, through the ‘philosophical’ reasoning approach and using worldwide successful EOR cases, the following three parameters were found to be the most important factors in running successful EOR applications, regardless of oil prices and risky investment costs, to extend the life span of the reservoir and warrant both short and long-term profit: (1) Proper technical design and implementation of the selected EOR method through continuous monitoring and re-engineering the project (how to apply more than what to apply), (2) good reservoir characterization and geological descriptions and their effect on the mechanics of the EOR process, and (3) paying attention to experience and expertise (human factor). It is believed that the systematic analysis and philosophical approach followed in this paper and the outcome will provide proper guidance to EOR projects for upcoming decades.
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