Experimental Analysis of Heavy Oil Recovery and CO2 Storage by Alternate Injection of Steam and CO2 in Deep Naturally Fractured Reservoir
- Khosrow Naderi (U Of Alberta) | Tayfun Babadagli (U. of Alberta)
- Document ID
- Society of Petroleum Engineers
- SPE Heavy Oil Conference Canada, 12-14 June, Calgary, Alberta, Canada
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 4.1.2 Separation and Treating, 5.10.1 CO2 Capture and Sequestration, 5.3.9 Steam Assisted Gravity Drainage, 1.8 Formation Damage, 4.1.9 Heavy Oil Upgrading, 4.3.3 Aspaltenes, 5.8.6 Naturally Fractured Reservoir, 4.3.4 Scale, 5.4 Enhanced Recovery, 4.1.5 Processing Equipment, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 5.7.2 Recovery Factors, 1.6.9 Coring, Fishing, 5.8.7 Carbonate Reservoir, 5.4.6 Thermal Methods, 5.4.2 Gas Injection Methods
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Steam injection in heavy-oil containing naturally fractured reservoir aims at heating matrix to reduce the viscosity and enhance gravity drainage. This technique, however, is not feasible in deep reservoirs. Hydrocarbon solvent injection is also
impractical due to low gravity of oil, heterogeneity, and retrieval of solvent diffused into matrix. A hybrid application of these two techniques was tested for deep reservoir conditions earlier (Steam Over Solvent Injection in Fractured Reservoirs
Method -SOS-FR) and proved success if applied suitably. The cost of hydrocarbon solvent and greenhouse gas concerns, however, entail investigations on other techniques and materials.
The use of CO2 in this type of process as solvent was considered and tested in this paper. Several issues are highly critical in this process. Like other hydrocarbon solvents used under non-isothermal conditions, the recovery process is highly
sensitive to pressure and temperature as they determine the miscibility level. Also important is the capability of CO2 to extract matrix oil. Our earlier studies with light oil showed that heavier ends can be extracted if enough time is allowed for
CO2 to interact with matrix oil. The same needs to be investigated for heavy-oils. Another dilemma was inverse proportionality of CO2 solubility with temperature. Steam (or heating) is inevitable to condition oil and decrease its viscosity before CO2 injection but temperature should be critically adjusted not to sacrifice CO2 solubility of oil.
To clarify all these points and determine optimal application conditions (duration of each cycles and CO2 soaking time), we conducted a series of experiments by soaking core samples saturated with heavy oil into steam first followed by CO2. In
the third cycle, steam (or hot water) was injected again to produce upgraded oil in the matrix. The experiments were performed under static conditions (soaking sandpacks and sandstone samples into steam or CO2 chambers) at different
temperatures and pressures to determine optimal application conditions for mutual goals; heavy oil recovery and CO2 storage in the matrix. Finally, the results were compared to those of experiments with hydrocarbon solvents from technical point of
view including storage benefits of CO2.
Heavy oils reserves have been receiving more attention recently as the oil prices are steadily high enough to surmount the associated expenses of oil production. In conjunction with this, technological advancements to improve heavy-oil recovery
have been reported but laboratory scale experiments are critically needed in optimal designing of the field tests.
Contrary to the conventional oil reservoirs, heavy oil reserves are lack of standardized methods. In addition to this, when the reservoirs show geological constrains, special methods are needed to take into account the diverse medium and fluid
properties of such reservoirs. Specifically, in the case of fractured reservoirs, the main problems are to mobilize the oil out of the tight matrix into fractures and distributing the heat uniformly to heat the matrix in order for this process to occur. The
common practice to reduce the heavy oil reluctancy to flow is to decrease its viscosity by providing heat and the most usual way to do that is steam injection. This method, on the other hand, has its own restrictions due to the high cost and heat losses if the reservoir is deep.
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