Modeling of a New Single-Well EOR Piloting Technique: Application to CO2 EOR
- Morten Rode Kristensen (Schlumberger Middle East SA.) | Cosan Ayan (Schlumberger) | Raghu Ramamoorthy (Schlumberger)
- Document ID
- Society of Petroleum Engineers
- Abu Dhabi International Petroleum Conference and Exhibition, 11-14 November , Abu Dhabi, UAE
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 2.5.2 Fracturing Materials (Fluids, Proppant), 5.6.1 Open hole/cased hole log analysis, 5.4.2 Gas Injection Methods, 1.6 Drilling Operations, 5.4.1 Waterflooding, 5.8.7 Carbonate Reservoir, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 4.3.4 Scale, 5.2 Reservoir Fluid Dynamics, 5.2.1 Phase Behavior and PVT Measurements, 5.2.2 Fluid Modeling, Equations of State, 1.6.9 Coring, Fishing, 5.3.4 Reduction of Residual Oil Saturation
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Screening and piloting of enhanced oil recovery (EOR) methods is often a lengthy process requiring large financial commitments. The reservoir uncertainty and, for some EOR methods, the lack of fundamental recovery mechanism understanding, call for a careful and staged screening and piloting program before committing to full-field implementation. The MicroPilot* single-well in situ EOR evaluation is a new piloting technique which allows for rapid and cost effective testing of EOR methods under in-situ downhole conditions. It is a log-inject-log technique conducted with a wireline formation tester, where a small quantity of EOR fluid is injected and the resulting change in oil saturation then determined based on a set of openhole logs that are run both before and after the injection.
The MicroPilot is a proven piloting technology for alkaline-surfactant-polymer (ASP) EOR. In this paper, we investigate the feasibility of extending this new technology for testing of CO2 EOR. We demonstrate through detailed analytical and numerical modeling that the changes in oil saturation and composition expected during the CO2 EOR process are measurable by the openhole logs when taking into account logging tool resolution. Based on a test library consisting of 13 different oils, which have been carefully characterized to match experimental PVT data, and all of which are likely candidate oils for miscible CO2 EOR, we investigate the expected pilot response when injecting CO2 both above and below the minimum miscibility pressure. We further study the sensitivity of the pilot response to gravity effects as well as residual oil saturation to the CO2 flood.
The MicroPilot was introduced as an intermediate step in the EOR screening process between laboratory testing and traditional multiwell field pilots (Arora et al. 2010). The technique works like a downhole laboratory by injecting a small quantity of the EOR fluid and measuring the resulting decrease in residual oil saturation. The MicroPilot is a small-scale log-inject-log technique that can be executed in a matter of hours to days, making it a relatively inexpensive step in the EOR screening process. After the target well is drilled for application of the technique, a suite of wireline openhole logs is run to determine the saturations, which reflect the remaining saturation after waterflood. A formation tester string is then used to inject the EOR fluid, typically 10 to 20 L, through a pencil-sized hole drilled into the side of the wellbore at the target depth. Following injection, the suite of openhole logs is run again to evaluate the effectiveness of the flood by measuring the change in oil saturation and the dimensions of the flood. Often the logging tools can be combined with the formation testing string so that the post-injection logs may be acquired within minutes after the injection. This is particularly recommended when the displacing or displaced fluids have low viscosity. Injection stations can be selected at multiple depths, thereby providing the ability to test an EOR method in different zones of the reservoir or to test different EOR fluids within a single zone, all within a single job. A schematic of the MicroPilot is shown in Fig. 1.
Arora et al. (2010) reported the first EOR MicroPilot which was conducted in a medium heavy-oil sandstone reservoir using a mixture of alkaline, surfactant, and polymer chemicals (ASP) as the EOR fluid. Flow modeling and analysis of this MicroPilot was subsequently presented by Cherukupalli et al. (2010). Edwards et al. (2011) reported the second application of the technique, which was conducted in a light-oil carbonate reservoir using an alkaline-surfactant mixture as the EOR fluid.
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