Evaluation of Steam Injection in a Fractured Heavy Oil Carbonate Reservoir in Iran
- Mehdi Bahonar (Petroleum U. of Tech Iran) | Abdolrahim Ataei (National Iranian Oil Co.) | Rahim Masoudi (National Iranian Oil Co.) | Seyed Mousa Mousavi Mirkalei (National Iranian Oil Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Middle East Oil and Gas Show and Conference, 11-14 March, Manama, Bahrain
- Publication Date
- Document Type
- Conference Paper
- 2007. Society of Petroleum Engineers
- 5.1.2 Faults and Fracture Characterisation, 5.5 Reservoir Simulation, 2.2.2 Perforating, 1.10 Drilling Equipment, 5.5.2 Core Analysis, 5.2 Reservoir Fluid Dynamics, 1.6.9 Coring, Fishing, 5.1.5 Geologic Modeling, 5.6.1 Open hole/cased hole log analysis, 5.4.6 Thermal Methods, 5.3.2 Multiphase Flow, 5.8.7 Carbonate Reservoir, 4.2.4 Risers, 4.3.3 Aspaltenes, 5.8.6 Naturally Fractured Reservoir, 5.7.2 Recovery Factors, 5.2.1 Phase Behavior and PVT Measurements, 5.4.1 Waterflooding
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Steam injection in naturally fractured heavy oil reservoirs provides an extremely challenging problem as well as a potentially effective and efficient improved oil recovery method. Coupling of the two distinct and contrasting matrix and fracture systems results in a highly non-linear problem, and it gets even more complicated as a result of steep changes in fluid properties due to the thermal effects of steam injection. Modeling and designing an optimum steam injection operation in such systems requires an accurate characterization and representation of a naturally fractured heavy oil reservoir and steam injection operation parameters and dynamics1.
In this communication, the results of a feasibility study of steam injection in a highly fractured carbonate reservoir are discussed. The field is a giant structure located in south west of Iran at the coast of Persian Gulf. It is a symmetrical anticline with 56 mile length and 10 mile width in the surface with about 3.6 billion barrels of initial oil in place. The initial pressure is 927 psi at 1700 ft depth. The gravity of the oil is 7.24 °API with viscosity of about 2700 cp.
The Geological model was constructed based on the available 2D and 3D seismic investigation and conventional core data from different samples. Extensive fracture characterization has been conducted using core data as well as the petrophysical interpretation using imaging logs. Dynamic reservoir simulation model with thermal option has been developed and used for optimization of different parameters for steam injection and their effect on reservoir performance and recovery factor.
Reservoir simulation of the field showed that steam injection could improve oil recovery from zero up to nearly 12 %. Furthermore, the results illustrated that the important parameters for designing the steam injection are different strategies for perforating, well spacing, well type, pattern type and size. Additionally, the effect of other parameters such as injected steam quality, oil-water capillary pressure in matrix blocks, steam injection and oil production rate have been studied.
The K Field is a highly fractured carbonate reservoir with about 3.6 billion barrels of initial oil in place. The two important formations in this field for oil production are Jahrum and Sarvak formations. Therefore, the field has been considered as the first developing extra heavy oil reservoir in Iran. Different scenarios were suggested for this field to put it on production among which steamflooding, cyclic steam stimulation and in situ combustion are the most promising methods because of their thermal nature.
Sarvak formation with the average thickness of 985 ft is one of the main formations in this field. Initial oil in place of Sarvak reservoir based on Montecarlo calculations program is estimated at 2.7 billion barrels of oil. Therefore, the reservoir simulation study was focused on this formation.
Steamflooding method is much like a waterflooding method since it is injected on a pattern basis. Full potential of Steamflooding method was not realized until commercial steamfloods were started in California2. After that many successful field test were reported in literature for both conventional and fracture reservoirs4, 5, 6. Additionally, it was successful both in light and heavy/ extra heavy oil reservoirs7. This is why we did reservoir simulation study based on this method.
The objective of this study is to apply all the available data to construct the most reliable model and then determine if the steamflooding method is a suitable candidate to be implemented in this reservoir. CMG thermal simulator (STARS module) with dual porosity option was chosen for our simulation study and the PVT was tuned by the WinProp module. After construction of the model, we attempted to optimize the most significant field operational parameters.
Geography and Geology of the Field
K Field is a giant structure located in the southwestern part of Iran in the coast of Persian Gulf. Exploration of the field occurred in 1959 in Jahrum and Sarvak formations as extra heavy oil reservoir.
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